CN102723880A - Alternating current-to-direct current circuit - Google Patents

Abstract

The invention discloses an alternating current-to-direct current circuit. The circuit comprises a rectification circuit, a BUCK circuit and a voltage detection control circuit, wherein the voltage detection control circuit is provided with a first preset valve used for limiting the lowest work voltage of the BUCK circuit and a second preset valve used for limiting the highest work voltage of the BUCK circuit, and is used for respectively detecting an instantaneous value of pulsating direct current and a voltage value of a low-voltage output end; the voltage detection control circuit outputs a PWM (pulse-width modulation) signal to control the BUCK circuit to work when the instantaneous value of the pulsating direct current is more than the preset vale and less than the second preset valve, and the output voltage Vout of the low voltage output end is less than a third preset value; and when the instantaneous value of the pulsating direct current is more than the second preset value, the voltage detection control circuit controls the BUCK circuit to stop working. The alternating current-to-direct current circuit has the advantages that the BUCK circuit works in a low voltage part of the pulsating direct current by limiting the highest work voltage of the BUCK circuit, so that the efficiency is improved, the circuit does not use high-voltage electrolytic capacitor, and the efficiency is high.

Description

A kind of AC-DC circuit

Technical field

The present invention relates to the AC-DC circuit, particularly be applied to the AC-DC circuit in the small-power AC/DC power supply.

Background technology

The AC-DC circuit is a lot, can realize with rectification circuit.Industry is generally adopted Alternating Current Power Supply with folk power supply, is example with civilian, and China is 220VAC/50Hz, and 120VAC or 110VAC are adopted in America; Frequency is the alternating current of 60Hz, and Britain adopts 240VAC/50Hz, and other countries and regions also have nothing in common with each other; All things considered, frequency are two kinds: 50Hz or 60Hz, and operating voltage is about 110V and about 220V; Be characterized in, the direction intercropping cyclic variation at any time of the amplitude of voltage (or electric current), as shown in Figure 1.

The alternating current that changes by sinusoidal rule in time shown in Fig. 1; Be called the alternation sinusoidal voltage, change the once needed time and be called cycle of alternating voltage, represent with T; The said 220V of industry; Be meant effective value, its peak value is

times effective value, is:

$220V\×\sqrt{2}=311.1V$

The size and Orientation of direct voltage (or electric current) does not change in time.As use curve representation voltage, then be the straight line parallel, but we are generally constant direction with horizontal time axis, but the size of voltage (or electric current) change to some extent in time be also referred to as direct voltage (or electric current).

Industrial and civilianly all need become direct current, at first will make the electric current folk prescription to flowing, be unilateal conduction, and then amplitude stabilization got off i.e. filtering exchanging.Be transformed into folk prescription to AC power and call rectification to the process of power supply.

Become low-voltage DC to AC rectification, transformer will be used in the centre, and volume is big; Change the turn ratio that output voltage will change transformer; Efficient is also low, after output adds capacitor filtering, finally is reflected to ac input end; All be that sine wave at alternating current just has operating current during near the top, cause the rugged change of ac power waveform.

" CONTROLIED ON-TIME BUCK PFC " United States Patent (USP) prospectus of U.S. Patent Publication US2010123448 shows a kind of buck pfc circuit, and sort circuit can be regarded as the circuit that a kind of interchange becomes low-voltage direct, by its disclosed technical scheme; Used the BUCK circuit; The PWM mode is controlled the switch in the BUCK circuit, and when input Rectified alternating current peak value, it is maximum relatively that duty ratio reaches; Need the inductance value of the inductance L in the BUCK circuit will be very big like this; And the operating current that this inductance L allows is also very big, so just can guarantee reaching under the high pressure input under the maximum relatively situation of duty ratio, and this inductance magnetic saturation can not occur; This has just determined that also the volume of inductance L is big, and the pressure-resistant treatments between the circle of winding and circle, layer and the layer increases many technologies and cost.

PWM refers to Pulse Width Modulation; The pulse width modulation signal; Comprise that deciding frequency changes pulse duration, and pulse frequency modulated (PFM:Pulse Frequency Modulation), and the combination of this dual mode is used; The said PWM of this paper refers to above-mentioned PWM and PFM and their compound mode PWM-PFM.

Common BUCK circuit is used under the Rectified alternating current input occasion, and when importing the voltage peaking of Rectified alternating current, it is minimum that duty ratio reaches, and switching loss is big, exists circuit efficiency low, the shortcoming that loss is big.

" a kind of AC-DC circuit " of one Chinese patent application numbers 201210056555 shows a kind of AC-DC circuit that is used for the small-power occasion, is used for the occasion of the above power output of 3W, and it is many also to have a current harmonics, the shortcoming that efficient is lower.

In the application scenario of power output less than 75W; All there is intrinsic deficiency in two kinds of above-mentioned schemes, and for the step-down pfc circuit with the BUCK circuit, the inductance value of the inductance L that need use will be very big; Volume is big, and the pressure-resistant treatments between the circle of winding and circle, layer and the layer increases many technologies, cost." a kind of AC-DC circuit " for above-mentioned exists current harmonics many, the deficiency that efficient is lower.

Annotate: 75W is data from CNS GB17625.1-1998, by name " the harmonic current limit value that low-voltage electrical and electronic equipment send (the every phase input current of equipment≤16A) ".

Add the two-step scheme of DC/DC for PFC, also have complicated circuit, the shortcoming that cost is higher with BOOST.And picture integrated circuit LNK302P on the market is the instead of linear of representative and the low-cost solution of capacitor step-down power supply, also need use high-pressure electrolysis electric capacity, to the Rectified alternating current filtering behind the commercial power rectification.

Summary of the invention

Have mirror so, the objective of the invention is provides a kind of AC-DC circuit in the application scenario of power output less than 75W, and its BUCK circuit need not adopt high-pressure electrolysis electric capacity and big volume inductance, and cost is lower, and has high relatively conversion efficiency.

For solving the problems of the technologies described above, comprise rectification circuit, voltage detecting and controling circuit, BUCK circuit; Described BUCK circuit is connected after the described rectification circuit, and the BUCK circuit is output as the low-voltage output of described AC-DC circuit; Described voltage detecting and controling circuit output pwm signal is controlled described BUCK circuit; Described rectification circuit output ripple direct current, described voltage detecting and controling circuit detect instantaneous value, the detection low-voltage output magnitude of voltage of Rectified alternating current, and described voltage detecting and controling circuit output pwm signal is in the requsst listed below controlled switch in the BUCK circuit:

When the galvanic instantaneous value of described rectification circuit output ripple was higher than first preset value, the pwm signal of described voltage detecting and controling circuit output was controlled described BUCK circuit working;

When the galvanic instantaneous value of described rectification circuit output ripple was higher than second preset value, the pwm signal of described voltage detecting and controling circuit output was closed, and described BUCK circuit quits work;

Described voltage detecting and controling circuit detects said low-voltage output magnitude of voltage, and when described low-voltage output magnitude of voltage surpasses the 3rd preset value, the pwm signal of described voltage detecting and controling circuit output is closed, and described BUCK circuit quits work.

Let the reliable work of such scheme, the voltage of described second preset value is higher than the described first preset value voltage;

Improvement as technique scheme; The voltage of described second preset value changes along with described low-voltage output voltage ripple; When described low-voltage output voltage ripple became big, the voltage of described second preset value was raise by described voltage detecting and controling circuit automatically; The voltage of described first preset value changes along with described low-voltage output voltage ripple, and when described low-voltage output voltage ripple became big, the voltage of described first preset value was reduced by described voltage detecting and controling circuit automatically.

Shunt capacitance in the middle of the output of said rectification circuit and the described BUCK circuit, described capacitance is below 1uF.

Operation principle of the present invention is:

The AC-DC circuit of above-mentioned annexation is when the instantaneous value of Rectified alternating current is higher after the rectification, when being higher than second preset value; The BUCK circuit is not worked, and the BUCK circuit working is higher than in a period of time scope of low-voltage output at the instantaneous value of Rectified alternating current, at this moment because the operating voltage not high (comparing with the peak value of Rectified alternating current after the rectification) of BUCK circuit; The duty ratio of BUCK circuit can be done greatlyyer; As between 0.99 to 0.1, conversion efficiency is done very highly easily, and when the instantaneous value of Rectified alternating current after the rectification is higher, (is higher than second preset value); The BUCK circuit is not worked; At this moment the inductance in the BUCK circuit does not bear instantaneous high pressure, and this inductance can be done lessly, and instantaneous high pressure is all born under cut-off state by the switching device in the BUCK circuit (being generally metal-oxide-semiconductor); Switching tube in the BUCK circuit is under cut-off state, and its stress that bears also promotes significantly.

Output and the middle shunt capacitance of BUCK circuit at rectification circuit; The envelope of the HF switch electric current that produces in the time of can letting the BUCK switch is clear; Capacitance is below 1uF, and the HF switch current filtering that produces in the time of can be to the BUCK switch improves EMI performance of the present invention.

Compared with prior art, the present invention has following beneficial effect:

To sum up analyze,, power on, do not have when starting shooting impulse current in start first because the only interval work of a section below the peak value of alternating current of the BUCK circuit among the present invention in the small-power power less than 75W, is not used the high-pressure electrolysis electric capacity of filtering; The electric stress that switching device in the BUCK circuit bears also reduces; Improve the duty ratio of switching device, thereby improved conversion efficiency; Only used the one-level Switching Power Supply, circuit is simple, and cost is low.

Owing to only use the filter capacitor of larger capacity, the easy paster production of other circuit, miniaturization easily, modularization at output.

Description of drawings

Fig. 1 is the ac power waveform figure that changes by sinusoidal rule in time;

The theory diagram of Fig. 2 for coming out according to drafting in the technical scheme; It also is the circuit diagram of first embodiment;

Fig. 3 is the Rectified alternating current figure ofrectification circuit 101 outputs;

Fig. 4 is operation interval, electric current envelope, the output ripple sketch map of first embodiment of the invention;

Fig. 5 is first embodiment of the invention actual measurement output ripple figure;

Fig. 6 is the second embodiment of the invention circuit diagram;

Fig. 7 is the third embodiment of the invention circuit diagram;

Fig. 8 is the another kind of application circuit of third embodiment of the invention;

Fig. 9 is the fourth embodiment of the invention circuit diagram;

Figure 10-1 is the operation interval sketch map of fourth embodiment of the invention;

Figure 10-2 is the electric current envelope sketch map of fourth embodiment of the invention;

Figure 10-3 is the output ripple sketch map of fourth embodiment of the invention;

Figure 11 is the fifth embodiment of the invention circuit diagram.

Embodiment

First embodiment

Fig. 2 shows the theory diagram of first embodiment of the invention, and the AC-DC circuit comprisesrectification circuit 101, voltage detecting and controling circuit 102,BUCK circuit 103 compositions.

Rectification circuit 101 is the AC rectification of input, the output ripple direct current, and referring to Fig. 3, transverse axis is a time shaft, and T representes the cycle of input AC electricity, and the longitudinal axis is the instantaneous voltage value of Rectified alternating current; Voltage detecting and controling circuit 102 detects the output voltage V out of low-voltage outputs simultaneously through the instantaneous value ofport 201 withport 202 detection Rectified alternating currents throughport 204, simultaneously through switch Q1 in theport 203 output pwm signalscontrol BUCK circuit 103; Switch Q1 is generally a metal-oxide-semiconductor.

BUCK circuit 103 is connected after therectification circuit 101, andBUCK circuit 103 comprises switch Q1, inductance L, sustaineddiode 1, and output filter capacitor C, and the basic circuit topology ofBUCK circuit 103 is known technologies, repeats no more here.The input of BUCK circuit is connected to the output ofrectification circuit 101, and promptly the output ripple direct current ofrectification circuit 101 is exactly the operating voltage ofBUCK circuit 103, andBUCK circuit 103 is output as the low-voltage output Vout of this AC-DC circuit;

Voltage detecting and controling circuit 102 is provided with second preset value that is used to limitBUCK circuit 103 maximum working voltages; And first preset value that is used to limitBUCK circuit 103 work lower limits; With the 3rd preset value that is used to limitBUCK circuit 103 maximum output voltages; The pwm signal output of voltage detecting and controling circuit 102 is connected to the work control end of BUCK circuit; Be that voltage detecting and controling circuit 102 is controlled the switch Q1 in the described BUCK circuit throughport 203 output pwm signals; When the galvanic instantaneous value ofrectification circuit 101 output ripples more than first preset value, below second preset value and low-voltage output output voltage V out when being lower than the 3rd preset value, voltage detecting and controling circuit 102 is 103 work of output pwm signals control BUCK circuit, 103 outputs of BUCK circuit obtain low-voltage DC after capacitor C filtering; When the galvanic instantaneous value ofrectification circuit 101 output ripples is higher than second preset value; Voltage detecting and controling circuit 102 is closed through the pwm signal ofport 203 outputs; Switch Q1 in theBUCK circuit 103 quits work; Be that switch Q1 is in off-state in the BUCK circuit, at thismoment BUCK circuit 103 is not worked, and the capacitor C energy storage is to the output load discharge; When low-voltage output Vout voltage was higher than the 3rd corresponding preset value, voltage detecting circuit 102 was also closedBUCK circuit 103, and promptly switch Q1 is in off-state in theBUCK circuit 103, in case output voltage V out surpasses the 3rd preset value of setting.

With one group of measured data explanation first embodiment of the present invention, designed output power is 12V/6W below.Rectification circuit 101 is made up of 4 1N5406 rectifier diodes, is connected into bridge rectifier, and BUCKcircuit 103 comprises switch Q1, sustaineddiode 1 and inductance L and capacitor C; Switch Q1 selects metal-oxide-semiconductor for use; Model is the metal-oxide-semiconductor SPU03N60C of scientific & technical corporation of Infineon, and its drain current is 3A, and withstand voltage is 600V; The pwm signal ofport 203 outputs is through the grid of isolating transformer driven MOS pipe Q1; In order to simplify circuit, represent this isolation drive with the grid of arrow points switch or sensing metal-oxide-semiconductor without exception among this paper, can realize also that with known bootstrap approach this " isolation " drives.The output that the drain electrode of metal-oxide-semiconductor Q1 connectsrectification circuit 101 just; The source electrode of metal-oxide-semiconductor Q1 continues and flows the negative electrode of diode D1; The anode ofsustained diode 1 connects the output ofrectification circuit 101 and bears; The tie point of the source electrode of metal-oxide-semiconductor Q1 and the negative electrode ofsustained diode 1 also is connected inductance L, and output filter capacitor C is connected with inductance L, and the filter capacitor C other end connects the output ofrectification circuit 101 and bears.

Low-voltage output Vout is 12V, and first preset value is taken as more than 12V * 1.05=12.6V so, gets 13V here as first preset value; After the minimum duty cycle D that considers metal-oxide-semiconductor Q1 was lower than below 0.05, the efficient of circuit was very low, and getting minimum duty cycle D here is 0.1, utilizes the output voltage computing formula of BUCK circuit so:

U_Vout=DU_InFormula (1)

In the formula (1), U_VoutBe low-voltage output Vout voltage, D is a duty ratio, U_InBerectification circuit 101 output ripple direct current instantaneous values.Can calculate second preset value is 120V.

The 3rd preset value is decided to be 12.85V.

Voltage detecting and controling circuit 102 can be that PWM controller and two adjustable shunting a reference sources of TL431 three ends and other device of UC2843A formed by ON company model; Voltage detecting, pwm control signal output function that theport 201 of above-mentioned voltage detecting and controling circuit 102,port 202,port 203 andport 204 are realized; All can realize by this circuit; The physical circuit of this circuit connects and principle all belongs to the known technology category, in this explanation no longer one by one.The switching frequency of this voltage detecting and controling circuit 102 is 52KHz.Inductance L is the power inductance of 100uH so, and capacitor C is the electrochemical capacitor of 2200uF/16V.

Measured performance such as following table one:

Table one

Output voltage	12V
		Output current	0.5A
Fully loaded output ripple (peak-to-peak value)	1.69V
		Efficient	81.4%
The ac input end peak inrush current	2.37A

Fig. 4 shows power supply industry oscillogram commonly used, and wherein T is 20mS, the 50Hz alternating current of corresponding China, and 301 is the output ripple direct voltage ofrectification circuit 101; 302 is the operation interval of theBUCK circuit 103 in the first embodiment of the invention; 303 is the envelope diagram of the input operating current ofBUCK circuit 103 in the first embodiment of the invention; 304 is the ripple voltage figure at the output capacitor C two ends ofBUCK circuit 103 in the first embodiment of the invention; Fig. 5 shows the ripple voltage figure at the output capacitor C two ends of first embodiment of the invention actual measurement.The oscilloscope model: Tyke TDS-3012C digital fluorescence oscilloscope, electronic load has been used in load, and model is IT8511, and current settings is on 0.5A.Among the waveform of Fig. 5 and Fig. 4 304 is on all four.

Obviously, let circuit when the load underloading, the BUCK circuit working is between first preset value 20V to the second preset value 60V; And at circuit at the load full load; The BUCK circuit working helps further conversion and raises the efficiency between first preset value 13V to the second preset value 120V, and the ripple voltage that voltage detecting and controling circuit 102 needs only output voltage V out detects; Can realize this function, promptly the BUCK operation interval is adjusted operation interval automatically with output ripple.

If a kind of control ON time buck pfc circuit that adopts " the CONTROLIED ON-TIME BUCK PFC " of U.S. Patent Publication 2010123448 in the background technology to illustrate; Be designed to the circuit of same output 12V/6W, its duty ratio D when exchanging input peak value 311V is:

$D=\frac{U_{\mathrm{Vout}}}{U_{\mathrm{In}}}=\frac{12}{311}=0.0386$Formula (2)

This duty ratio is its maximum duty cycle; Exchange the input instantaneous value littler than peak value 311V At All Other Times in; Its duty ratio D is little more than above-mentioned 0.0386; For the technical staff in present technique field, duty ratio is less than 0.05, and the conversion efficiency of circuit is being known Chang Zhi with carrying out under the cost.U.S. Patent Publication US2010123448 is fit to make the higher circuit of output voltage, and like output 200V, maximum duty cycle is 0.64 so, and circuit just has feasibility.

Common BUCK circuit is used under the Rectified alternating current input occasion, and when input Rectified alternating current peaking 311V, it is minimum that duty ratio reaches, the result of calculation of formula (2), and at this moment switching loss is big, exists circuit efficiency low, the shortcoming that loss is big.The same with above-mentioned U.S. Patent Publication US2010123448, metal-oxide-semiconductor all will use the above metal-oxide-semiconductor of withstand voltage 600V, could guarantee that like this final products are meeting the requirements aspect surge, the lightning protection; In fact, want to make and accomplish the product that meets safety, because metal-oxide-semiconductor all is work exchanging in most time of input; The essential metal-oxide-semiconductor that uses withstand voltage 900V, and the circuit of first embodiment of the invention are when input voltage instantaneous value 120V is above; Metal-oxide-semiconductor Q1 is idle; Transistor its electric stress that bears when ending is 2 to 10 times under the conducting state, so the metal-oxide-semiconductor in the first embodiment of the invention can be selected withstand voltage low relatively transistor, same like this price for use; Can select the low metal-oxide-semiconductor of conducting internal resistance for use, promote the conversion efficiency of circuit of the present invention.

And " a kind of AC-DC circuit " of one Chinese patent application numbers 201210056555 shows a kind of AC-DC circuit that is used for the small-power occasion; Adopt the circuit of Figure 17 in its application, triode type selecting for ease, the NPN type all changes positive-negative-positive in the circuit; Positive-negative-positive all changes the NPN type into; Be designed to export the circuit of 12V/6W, output capacitance is still used 2200uF/16V electric capacity, measured performance such as following table two:

Table two

Output voltage	12V
		Output current	0.5A
Fully loaded output ripple (peak-to-peak value)	2.26V
		Efficient	64.2%
The ac input end peak inrush current	28.6A

In order to obtain the performance of table two; TR25a has selected the MJE13003 triode for use, and TR25b has selected for use maximum collector current up to 12A, this large power triode of the 3DD13009 of withstand voltage 400V; And 5 parallel connections have been adopted; Just guaranteed in the table two 64.2% efficient, clearly, ripple and efficient all are not so good as the data in the table two.Because the circuit of application number 201210056555 is moment conductings when the input Rectified alternating current is slightly higher than 12V output voltage, the duration actual measurement of conducting is 96uS, and the peak current during conducting is very big, and actual measurement is up to 28.6A.

Obviously, the present invention in the following small-power occasion of 75W, can realize the described beneficial effect of preamble really.

Second embodiment

Fig. 6 is the schematic diagram of second embodiment of the invention, and the AC-DC circuit of second embodiment comprisesrectification circuit 101, voltage detecting and controling circuit 102,BUCK circuit 103 compositions; It is on the basis of embodiment one; Sustained diode in theBUCK circuit 1 is replaced by the metal-oxide-semiconductor Q2 of a N raceway groove; Metal-oxide-semiconductor Q2 plays afterflow here, and function is identical withsustained diode 1, because change the metal-oxide-semiconductor withsustained diode 1 synchronous conducting into; Conduction voltage drop is low, and the conversion efficiency of complete machine is high like this.

Rectification circuit 101 is with the AC rectification of input, and the output ripple direct current is referring to Fig. 3; Voltage detecting and controling circuit 102 detects the output voltage V out of low-voltage outputs simultaneously through the instantaneous value ofport 201 withport 202 detection Rectified alternating currents throughport 204, simultaneously through switch Q1 in theport 203 output pwm signals controlBUCK circuit 103; Be generally a metal-oxide-semiconductor; Voltage detecting and controling circuit 102 through switch Q2 in theport 205 output pwm signals controlBUCK circuit 103, is realized synchronous rectification simultaneously.

BUCK circuit 103 is connected after therectification circuit 101; Receive the Rectified alternating current ofrectification circuit 101 outputs; Add thecapacitor C 1 of absorbing high-frequency switching current in the middle of them, value is 104/630V, andBUCK circuit 103 is output as the low-voltage output Vout of this AC-DC circuit;

Voltage detecting and controling circuit 102 is provided with second preset value that is used to limit BUCK circuit 103 maximum working voltages; And the 3rd preset value that is used to limit first preset value of BUCK circuit 103 work lower limits and is used to limit BUCK circuit 103 maximum output voltages; The pwm signal output of voltage detecting and controling circuit 102 is connected to the work control end of BUCK circuit; Be that voltage detecting and controling circuit 102 is controlled switch Q1, switch Q2 in the described BUCK circuit through port 203,205 output pwm signals; When the galvanic instantaneous value of rectification circuit 101 output ripples more than first preset value, below second preset value and low-voltage output output voltage V out when being lower than the 3rd preset value; Just output pwm signal control BUCK circuit 103 work, 103 outputs of BUCK circuit obtain low-voltage DC after capacitor C filtering; When the galvanic instantaneous value of rectification circuit 101 output ripples is higher than second preset value; Voltage detecting and controling circuit 102 is closed through the pwm signal of port 203 outputs; Switch Q1 in the BUCK circuit 103 quits work; Be that switch Q1 is in off-state in the BUCK circuit, at this moment BUCK circuit 103 is not worked, and the capacitor C energy storage is to the output load discharge; When low-voltage output Vout voltage was higher than the 3rd corresponding preset value, voltage detecting circuit 102 was also controlled and is closed BUCK circuit 103, and promptly switch Q1 is in off-state in the BUCK circuit 103, in case output voltage V out surpasses the 3rd preset value of setting.

With one group of measured data explanation second embodiment of the present invention, designed output power is 24V/12W below.Rectification circuit 101 is made up of 4 1N5406 rectifier diodes, is connected into bridge rectifier, and BUCK circuit 103 comprises switch Q1, metal-oxide-semiconductor Q2 and inductance L; Switch Q1 model is the metal-oxide-semiconductor SPU03N60C of scientific & technical corporation of Infineon; Its drain current is 3A, and withstand voltage is 600V, and metal-oxide-semiconductor Q2 is the SI7450 of VISHAY company; Its drain current is 5A, and withstand voltage is 200V; The pwm signal of port 203 outputs is through the grid of isolating transformer driven MOS pipe Q1; The output that the drain electrode of metal-oxide-semiconductor Q1 connects rectification circuit 101 just; The source electrode of metal-oxide-semiconductor Q1 connects the drain electrode of synchronous freewheeling metal-oxide-semiconductor Q2; The source electrode of metal-oxide-semiconductor Q2 connects the output of rectification circuit 101 and bears, and the source electrode of metal-oxide-semiconductor Q1 also is connected inductance L with the tie point of the drain electrode of afterflow metal-oxide-semiconductor Q2; The pwm signal of port 205 outputs is directly controlled the grid of afterflow metal-oxide-semiconductor Q2, and the end of output filter capacitor C and an end of inductance L are connected, and the filter capacitor C other end connects the output of rectification circuit 101 and bears.

Low-voltage output Vout is 24V, and first preset value is taken as more than 24V * 1.05=25.2V so, and first preset value is got 30V here; After the minimum duty cycle D that considers metal-oxide-semiconductor Q1 was lower than below 0.05, the efficient of circuit was very low, and getting minimum duty cycle D here is 0.13; Utilize the output voltage computing formula (1) of BUCK circuit so; Can calculate second preset value is 184V, and this value can not exceed the withstand voltage of afterflow metal-oxide-semiconductor Q2, and leaves surplus.

The 3rd preset value is got the value that is lower than below the first preset value 30V, gets 24.7V here.

Voltage detecting and controling circuit 102 can be that PWM controller and the two adjustable shunting a reference sources of TL431 three ends of FAN7930 and synchronous freewheeling drive circuit that other device is formed constitute by the Fairchild Semiconductor model; Voltage detecting, pwm control signal output function that theport 201 of above-mentioned voltage detecting and controling circuit 102,port 202,port 203,port 204 andport 205 are realized; All can realize by this circuit; The physical circuit of this circuit connects and principle all belongs to the known technology category, in this explanation no longer one by one.The switching frequency of this voltage detecting and controling circuit 102 is for being fixed as 200KHz.Inductance L is the power inductance of 47uH so, and capacitor C is the electrochemical capacitor of 2200uF/25V.

Measured performance such as following table three:

Table three

Output voltage	24V
		Output current	0.5A
Fully loaded output ripple (peak-to-peak value)	1.35V
		Efficient	83.2%
The ac input end peak inrush current	1.74A

Owing to addcapacitor C 1, under the prerequisite that power increases, the ac input end peak inrush current obviously reduces, and the synchronous freewheeling pipe Q2 of adding has also obviously improved the conversion efficiency of circuit.Waveform correlation and actual measurement ripple are no longer listed because similar with first embodiment here.Obviously, the present invention in the following small-power occasion of 75W, can realize the described beneficial effect of preamble really.

Obviously; Let circuit when the load underloading, the BUCK circuit working between first preset value 50V to the second preset value 120V, and at circuit at the load full load; The BUCK circuit working is between first preset value 30V to the second preset value 184V; Help further conversion and raise the efficiency, the ripple voltage that voltage detecting and controling circuit 102 needs only output voltage V out detects, and can realize this function.

The output ripple of above-mentioned two embodiment is bigger, and it is fully passable being used for the driving LED lamp, and control flows is crossed the maximum current of LED lamp, guarantees that the LED lamp is not damaged.Because the efficient of BUCK circuit is high; Loop response is good, inserts second level BUCK circuit, second level BUCK circuit continuous firing at above-mentioned two embodiment outputs; Final like this output voltage ripple can be done very for a short time, so that give the subsequent conditioning circuit power supply that requires than higher.

In fact, this programme is used for the isolated variable power supply, equally can realize goal of the invention; For the technical staff of Switching Power Supply industry, circuit of reversed excitation (FLY-BACK) in fact is exactly a kind of distortion of BUCK circuit, and the transformer in the circuit of reversed excitation is not a transformer truly; In fact be exactly the inductance of isolated (having doublewound), its effect of energy storage inductor of having held concurrently is called the energy storage transformer; Output voltage is only relevant with load, and is irrelevant with the turn ratio, because circuit is in case realize isolating; Output not only can realize step-down, can also realize boosting, so circuit of reversed excitation is called a desirable version of isolating of BUCK-BOOST converter again." Switching Power Supply power inverter topology and design " the 60th page of text of front page first that please refer to the Zhang Xingzhu work gone and first section the ISBN:978-7-5083-9015-4 of this book.Or the 237th page of text of " principle of Switching Power Supply and design " revised edition first row of Zhang Zhansong, Cai Xuansan work and and first section.

Shown in the 3rd embodiment is exactly this power supply that is used for isolated variable, comprises anti-sharp and normal shock.

The 3rd embodiment

Fig. 7 shows the schematic diagram of third embodiment of the invention; Known; Circuit of reversed excitation is a kind of distortion of BUCK circuit, promptly changes the switch Q1 position among Fig. 2 into energy storage inductor L, and changes the position of formersustained diode 1 into switch Q1; The position of former inductance L changessustained diode 1 into, and diode D1 generally is rectifier diode at reposition.Energy storage inductor L here is exactly the energy storage transformer, and the circuit of reversed excitation that obtains like this is identical with the operation principle of BUCK circuit in essence, because circuit of reversed excitation is a kind of special circuit form of BUCK circuit.

The AC-DC circuit of the 3rd embodiment comprisesrectification circuit 101, voltage detecting and controling circuit 102, adopts theBUCK circuit 103 of circuit of reversed excitation structure to form.Annotate: omitted the circuit that degaussing is used among Fig. 7, claimed clamp circuit again, like the DCR clamp circuit of forming by diode, electric capacity, resistance.

Rectification circuit 101 is with the AC rectification of input; The output ripple direct current; Referring to Fig. 3; Voltage detecting and controling circuit 102 detects the instantaneous value of Rectified alternating currents throughport 201 andport 202, detects the output voltage V out of low-voltage outputs simultaneously through port 204,204 with the intermediate circuit of output becircuit 206 such as known light-coupled isolation; Voltage detecting and controling circuit 102 is simultaneously through switch Q1 in theport 203 output pwm signals controlBUCK circuit 103; Be generally a metal-oxide-semiconductor.

BUCK circuit 103 is connected after therectification circuit 101, receives the Rectified alternating current ofrectification circuit 101 outputs, andBUCK circuit 103 is output as the isolation low-voltage output Vout of this AC-DC circuit;

Voltage detecting and controling circuit 102 is controlled the switch Q1 in the describedBUCK circuit 103 throughport 203 output pwm signals; When the galvanic instantaneous value ofrectification circuit 101 output ripples more than first preset value, below second preset value and low-voltage output output voltage V out when being lower than the 3rd preset value; 103 work of voltage detecting and controling circuit 102 output pwm signals control BUCK circuit, 103 outputs of BUCK circuit obtain low-voltage DC after capacitor C filtering; When the galvanic instantaneous value ofrectification circuit 101 output ripples is higher than second preset value; Voltage detecting and controling circuit 102 is closed through the pwm signal ofport 203 outputs; Switch Q1 in theBUCK circuit 103 quits work; Be that switch Q1 is in off-state in theBUCK circuit 103, at thismoment BUCK circuit 103 is not worked, and the capacitor C energy storage is to the output load discharge; When low-voltage output Vout voltage was higher than the 3rd corresponding preset value, voltage detecting circuit 102 was also controlled and isclosed BUCK circuit 103, and promptly switch Q1 is in off-state in theBUCK circuit 103, in case output voltage V out surpasses the 3rd preset value of setting.

TheBUCK circuit 103 of present embodiment adopts the circuit of reversed excitation structure; Can boosting inverter; The benefit that circuit brings is thatBUCK circuit 103 can be started working from the approximate 0V of input pulsating dc voltage; Berectification circuit 101 output ripple direct voltages from very low voltage, the metal-oxide-semiconductor Q1 among the 3rd embodiment just can be operated in the on off state of PWM.Certainly, in order to let circuit work better, the source electrode of metal-oxide-semiconductor Q1 also can connect known current detection circuit.Promptly in the present embodiment circuit of reversed excitation, first preset value can be lower than the 3rd preset value.

Obviously, third embodiment of the invention realizes the repertoire of isolated converter really in the following small-power occasion of 75W, can realize the described beneficial effect of preamble equally, and its detailed principle repeats no more.

Shown in Fig. 7 is the anti exciting converter power supply that the present invention is applied to isolated variable; In fact; Basic forward converter also is the distortion of BUCK circuit; The 28th page of 3.1 joint of " Switching Power Supply power inverter topology and design " front page that please refer to Zhang Xingzhu work be to 29 pages of centres, or the 263rd page of text of " principle of Switching Power Supply and design " revised edition first row of Zhang Zhansong, Cai Xuansan work and and first section.

Fig. 8 shows the another kind of form of the 3rd embodiment; The present invention is used to isolate the electrical schematic diagram of forward conversion, on the basis of Fig. 7, the output winding end reversal connection of the same name of energy storage inductor L (energy storage transformer) once; Seal inafterflow inductance L 1 among the output rectification triode D1; Add sustained diode 2, as shown in Figure 8,empty frame 103 interior annexations are known technology among Fig. 8; Its principle is discussed very detailed in the middle of " Switching Power Supply power inverter topology and design " front page of Zhang Xingzhu work saves for the 28th page 3.1 to 29 pages, repeats no more here.

As long as adopt same control mode: voltage detecting and controling circuit 102 is controlled the switch Q1 in the describedBUCK circuit 103 throughport 203 output pwm signals; When the galvanic instantaneous value ofrectification circuit 101 output ripples more than first preset value, below second preset value and low-voltage output output voltage V out when being lower than the 3rd preset value; 103 work of voltage detecting and controling circuit 102 output pwm signals control BUCK circuit, 103 outputs of BUCK circuit obtain low-voltage DC after L1 and capacitor C filtering; When the galvanic instantaneous value ofrectification circuit 101 output ripples is higher than second preset value; Voltage detecting and controling circuit 102 is closed through the pwm signal ofport 203 outputs; Switch Q1 in theBUCK circuit 103 quits work; Be that switch Q1 is in off-state in theBUCK circuit 103, at thismoment BUCK circuit 103 is not worked, and the capacitor C energy storage is to the output load discharge; When low-voltage output Vout voltage was higher than the 3rd corresponding preset value, voltage detecting circuit 102 was also controlled and isclosed BUCK circuit 103, and promptly switch Q1 is in off-state in theBUCK circuit 103, in case output voltage V out surpasses the 3rd preset value of setting.

The another kind of form of the 3rd embodiment has equally realized goal of the invention,

Above-mentioned three embodiment not only can be used in single-phase alternating current, for the technical staff in present technique field, are used for the occasion of three-phase alternating current input, can realize goal of the invention equally, and it is exactly this application that the 4th embodiment illustrates.

The 4th embodiment

Fig. 9 shows the schematic diagram of the 4th embodiment, and referring to Fig. 9,empty frame 104 is an AC power, and the power supply inside shown in the figure is Y connection, and delta connection is the same, wherein A, B, three binding posts difference of C corresponding A, B, C three-phase.Empty frame 105 is the following half-bridge in the rectification circuit, is made up of diode Da, Db, Dc; Going up half-bridge in the rectification circuit is directly substituted by three tunnelmain body circuit 30a of the present invention, 30b, 30c;Circuit 30a, 30b, 30c structure are identical; All be made up of voltage detecting and controling circuit 102, BUCK circuit 103,102 suffix among Fig. 9 add a, and expression is the corresponding service aisle of A in the three-phase alternating current; Switching tube Q1 and continued flow tube D1 and inductance L adopt same marker method, show the passage at their places.

Operation principle based on first embodiment;Circuit 30a, 30b, 30c supply power to output end vo ut in turn; Reduced output ripple like this; And balance the electricity consumption of A, B, C three-phase, Figure 10-1 shows operation interval, electric current envelope, the output ripple sketch map of fourth embodiment of the invention to Figure 10-3; Wherein T is 20mS, and the 50Hz alternating current of corresponding China, output voltage are 48V, and output current is the oscillogram of 1A, and A, B, C are corresponding three-phase alternating current oscillogram, and the peak value of 380VAC is 537V, and the operation interval of 3 passages of Fig. 9 circuit is:

1,circuit 30a is operated in a-c and two intervals of a-b, and a-c is meant theBUCK circuit 103a work of 30a passage, and to capacitor C charging among Fig. 9, electric current flows back to the C phase in the three-phase electricity through diode Dc; A-b is meant theBUCK circuit 103a work of 30a passage, and to capacitor C charging among Fig. 9, electric current flows back to the B phase in the three-phase electricity through diode Db; In Figure 10-1,circuit 30a operation interval is represented with filling oblique brick wall.

2,circuit 30b is operated in b-c and two intervals of b-a, and b-c is meant the BUCK circuit 103b work of 30b passage, and to capacitor C charging among Fig. 9, electric current flows back to the C phase in the three-phase electricity through diode Dc; B-a is meant the BUCK circuit 103b work of 30b passage, and to capacitor C charging among Fig. 9, electric current flows back to the A phase in the three-phase electricity through diode Da;Circuit 30b operation interval is represented with filling starlike point.

3,circuit 30c is operated in c-b and two intervals of c-a, and c-b is meant the BUCK circuit 103c work of 30c passage, and to capacitor C charging among Fig. 9, electric current flows back to the B phase in the three-phase electricity through diode Db; C-a is meant the BUCK circuit 103c work of 30c passage, and to capacitor C charging among Fig. 9, electric current flows back to the A phase in the three-phase electricity through diode Da;Circuit 30b operation interval is represented with filling parallel vertical moulding.

303 indications is the electric current envelope diagram of respective channel among Figure 10-2, and the sign of corresponding passage in can 10-1 with the aid of pictures like electric current envelope piece figure under the operation interval of c-b indication, is exactly the operating current envelope diagram of 30c passage.

304 is the ripple voltage figure at output capacitor C two ends in the fourth embodiment of the invention among Figure 10-3; Owing to be three-phase input, each continues between mutually good, so output ripple is less, can prove, when second preset value of each passage is crest voltage one half of phase voltage, 3 passages just do not have gap work, and it is minimum that output ripple has at this moment reached.

The waveform of Figure 10-1,10-2,10-3 series is consistent with the result that Computer Simulation is come out.

In fact, because voltage detecting andcontroling circuit 102a, 102b, 102c are altogether, three voltage detecting and controling circuits among Fig. 9 can be optimized for one; And common metal-oxide-semiconductor, owing in the body parasitic diode is arranged all, cause that easily electric current is through inductance L; Pass through anti-filling of metal-oxide-semiconductor endoparasitism diode again, thus 6 complete rectifier diodes will be used, and in the circuit; When second preset value of each passage is that the crest voltage of phase voltage is half the when following, the inductance in 3 passages can be merged into one, and fly-wheel diode can be merged into one; It is exactly the circuit after this differentiation that Figure 11 provides, this circuit just shown in the 5th embodiment.

The 5th embodiment

The 5th embodiment is by the 4th embodiment optimization, referring to Figure 11, and the voltage detecting and controling circuit 102 among Figure 11; 3 detection port 201a, 201b, 201c are arranged, and the instantaneous voltage that detects three-phase is poor, also has adetection port 204; Detect output voltage V out; Voltage detecting and controling circuit 102 is exported corresponding three road pwm signal 203a, 203b, 203c respectively, controls Q1a, Q1b, Q1c respectively, and three road pwm signal 203a, 203b, 203c are under any circumstance; Have only one the tunnel output is arranged, in addition the two-way no-output.Fly-wheel diode can be merged into one, issustained diode 1, and this circuit has the low advantage of cost owing to only used an inductance L and asustained diode 1.

Fig. 9 and Figure 11 are applied to three-phase three-wire system, and for those skilled in the art, the occasion of circuit application of the present invention in three-phase four-wire system, circuit is simple relatively, realize easily, no longer give unnecessary details with embodiment here.Only be preferred implementation of the present invention below, should be pointed out that above-mentioned preferred implementation should not be regarded as limitation of the present invention, protection scope of the present invention should be as the criterion with claim institute restricted portion.Said as preamble; The BUCK circuit that the present invention sayed comprises the basic circuit form of BUCK circuit; Like the BUCK circuit 103 among the embodiment one, also comprise the distortion of BUCK circuit basic circuit form in the known technology, like the BUCK circuit 103 among embodiment two and the embodiment three.And also have other form based on the distortion circuit of BUCK circuit working principle; For those skilled in the art, do not breaking away from the spirit and scope of the present invention, can also make some improvement and retouching; As use bipolar transistor to replace above-mentioned FET; Adopt known triode multiple tube to replace corresponding triode, can not be exhaustive at this, but these improvement and retouching also should be regarded as protection scope of the present invention.

Claims (5)

1. an AC-DC circuit comprises rectification circuit, voltage detecting and controling circuit, BUCK circuit; Described BUCK circuit is connected after the described rectification circuit, and the BUCK circuit is output as the low-voltage output of described AC-DC circuit; Described voltage detecting and controling circuit output pwm signal is controlled described BUCK circuit; Described rectification circuit output ripple direct current; Described voltage detecting and controling circuit detects instantaneous value, the detection low-voltage output magnitude of voltage of Rectified alternating current; It is characterized in that: said voltage detecting and controling circuit is provided with second preset value that is used to limit BUCK circuit maximum working voltage, first preset value that is used to limit BUCK circuit working lower limit; With the 3rd preset value that is used to limit BUCK circuit maximum output voltage, described voltage detecting and controling circuit output pwm signal is in the requsst listed below controlled switch in the BUCK circuit:

When the galvanic instantaneous value of described rectification circuit output ripple was higher than first preset value, the pwm signal of described voltage detecting and controling circuit output was controlled described BUCK circuit working;

When the galvanic instantaneous value of described rectification circuit output ripple was higher than second preset value, the pwm signal of described voltage detecting and controling circuit output was closed, and described BUCK circuit quits work;

Described voltage detecting and controling circuit detects said low-voltage output magnitude of voltage, and when described low-voltage output magnitude of voltage surpasses the 3rd preset value, the pwm signal of described voltage detecting and controling circuit output is closed, and described BUCK circuit quits work.

2. AC-DC circuit according to claim 1 is characterized in that: the voltage of described second preset value is higher than the described first preset value voltage.

3. AC-DC circuit according to claim 1 and 2; It is characterized in that: the voltage of described second preset value changes along with described low-voltage output voltage ripple; When described low-voltage output voltage ripple became big, the voltage of described second preset value was raise by described voltage detecting and controling circuit automatically.

4. AC-DC circuit according to claim 3; It is characterized in that: the voltage of described first preset value changes along with described low-voltage output voltage ripple; When described low-voltage output voltage ripple became big, the voltage of described first preset value was reduced by described voltage detecting and controling circuit automatically.

5. AC-DC circuit according to claim 1 is characterized in that: shunt capacitance in the middle of the output of said rectification circuit and the described BUCK circuit, described capacitance is below 1uF.

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