A kind of load detection method, detection circuit and apply its switch power supplyTechnical field
The present invention relates to technical field of semiconductors, it is specifically related to be used in load detection method and the detection circuit of switch power supply.
Background technology
Inverse-excitation type switch power-supply can realize the isolation of former limit and secondary, and output voltage easily regulates, and the secondary at inverse-excitation type switch power-supply has a rectifier usually, so that the voltage of alternating current of transformer vice-side winding or electric current to be converted to the volts DS needed for load or electric current. In order to reduce the loss of rectifier, usually with the relatively low metal oxide semiconductor field effect transistor (MOSFET) of conducting resistance as synchronous rectifier, the mode of this kind of synchronous rectification can improve the efficiency of conversion of power supply.
It is illustrated in figure 1 the circuit block diagram of a kind of inverse-excitation type switch power-supply of prior art, secondary has a switching tube Q2 as synchronous rectification switch, the switch state of rectifier control circuit 101 trip switch pipe Q2, including synchronous rectification driving circuit and synchronous commutating control circuit in rectifier control circuit, both directly power by output voltage. , as shown in Figure 1, in addition inverse-excitation type switch power-supply of the prior art by diode D1 and resistor voltage divider network to obtain the sampled voltage V characterizing output voltage informationoff, compare sampled voltage V by comparer afterwardsoffWith the reference voltage V of settingREF, as sampled voltage VoffLower than described reference voltage VREFTime, judge that described switch power supply is in zero load or underloading.
According to the schematic circuit of the switch power supply shown in Fig. 1, if switch power supply is under underloading state, the power supply of synchronous commutating control circuit keeps power supply. Generally speaking, the service voltage of synchronous commutating control circuit is at about 3.0-3.5V, and output voltage is in higher situation, such as about 12-19V, the pressure reduction of this part can be bigger, its power consumption brought also can be bigger, and especially under underloading state, the efficiency of switch power supply will be produced very big impact by bigger power consumption.
Summary of the invention
In view of this, the present invention disclose a kind of be applied in switch power supply load detection method and detection circuit, the voltage between the first power end of synchronous rectification switch and the 2nd power end is detected by load detecting circuit, to judge the switch state of power switch pipe in described inverse-excitation type switch power-supply accordingly, when described power switch pipe is in shutoff state, and shutoff state is when lasting till default time interval, then judge that the output of described inverse-excitation type switch power-supply is in unloaded or underloading state.
According to the load detection method of a kind of switch power supply of the present invention, it is applied in inverse-excitation type switch power-supply,
Monitor the voltage between the first power end of the synchronous rectification switch in described inverse-excitation type switch power-supply and the 2nd power end,
Voltage change between the first power end according to described synchronous rectification switch and the 2nd power end judges the switch state of power switch pipe in described inverse-excitation type switch power-supply, wherein,
When described power switch pipe is in shutoff state, and when shutoff state lasts till default time interval, then judge that the output of described inverse-excitation type switch power-supply is in unloaded or underloading state.
Preferably, sample and keep the voltage between the first power end of described synchronous rectification switch and the 2nd power end, obtain a sampling sustaining voltage;
When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is less than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that declines;
When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is greater than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that rises.
Preferably, when the voltage between first power end and the 2nd power end of described synchronous rectification switch starts to rise, characterize described power switch pipe and start conducting;
When voltage between first power end and the 2nd power end of described synchronous rectification switch starts to decline, characterize described power switch pipe and start to turn off.
Preferably, judge that the shutoff state of described power switch pipe lasts till that the concrete steps of default time interval comprise:
Utilizing a charging current to be charged by one electric capacity, utilize the charging and discharging state of electric capacity described in controlled on-off control, the both end voltage of described electric capacity is as slope voltage, and wherein, the switch state of described controlled switch is identical with the switch state of described power switch pipe;
When described controlled switch disconnects, described slope voltage continues to rise, and the shutoff state that the time of the voltage threshold value that described slope voltage rise is extremely preset is described power switch pipe lasts till default time interval.
According to the load detecting circuit of a kind of switch power supply of the present invention, it is applied in inverse-excitation type switch power-supply,
Described load detecting circuit monitors the voltage between the first power end of the synchronous rectification switch in described inverse-excitation type switch power-supply and the 2nd power end, and the switch state of power switch pipe in described inverse-excitation type switch power-supply is judged according to the voltage change between the first power end of described synchronous rectification switch and the 2nd power end
Wherein, when described power switch pipe is in shutoff state, and when shutoff state lasts till default time interval, then judge that the output of described inverse-excitation type switch power-supply is in unloaded or underloading state.
Further, described load detecting circuit comprises voltage sampling circuit, and voltage sampling circuit comprises sampling hold circuit and comparison circuit,
Described sampling hold circuit is sampled and is kept the voltage between the first power end of described synchronous rectification switch and the 2nd power end, obtains a sampling sustaining voltage;
Voltage between first power end of described comparison circuit more described sampling sustaining voltage and the in real time described synchronous rectification switch of sampling and the 2nd power end,
When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is less than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that declines; When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is greater than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that rises.
Further, when the voltage between first power end and the 2nd power end of described synchronous rectification switch starts to rise, characterize described power switch pipe and start conducting;
When voltage between first power end and the 2nd power end of described synchronous rectification switch starts to decline, characterize described power switch pipe and start to turn off.
Further, described load detecting circuit comprises charge-discharge circuit and status signal generation circuit further,
Described charge-discharge circuit comprises current source and the electric capacity of series connection, and with the controlled switch of Capacitance parallel connection, controlled switch controls its switch action by the output signal of comparison circuit, and the both end voltage of charging capacitor is slope voltage, when described controlled switch disconnects, described slope voltage continues to rise;
Described status signal generation circuit receives described slope voltage and a voltage threshold value preset, and when described slope voltage rise is to described voltage threshold value, status signal generation circuit produces the status signal of a sign load information.
According to a kind of inverse-excitation type switch power-supply of the present invention, comprise power stage circuit, rectifier control circuit and above-mentioned load detecting circuit,
The output signal of described load detecting circuit is transferred to described rectifier control circuit;
Described rectifier control circuit is in order to control the switch state of synchronous rectification switch in described power stage circuit, and it comprises synchronous commutating control circuit and synchronous rectification driving circuit, and utilizes auxiliary power supply circuit to be powered by described synchronous commutating control circuit.
Further, described auxiliary power supply circuit comprises and the transformer coupled auxiliary winding in described inverse-excitation type switch power-supply, rectification diode and the first electric capacity.
Above-mentioned load detecting circuit monitors the voltage between the first power end of the synchronous rectification switch in inverse-excitation type switch power-supply and the 2nd power end by load detecting circuit, to judge the switch state of power switch pipe in described inverse-excitation type switch power-supply accordingly, when described power switch pipe is in shutoff state, and shutoff state is when lasting till default time interval, then judge that the output of described inverse-excitation type switch power-supply is in unloaded or underloading state. In addition, the present invention adopt auxiliary power supply circuit powered by synchronous commutating control circuit, when being in zero load or underloading state when load, synchronous commutating control circuit is powered can be lower, can not producing bigger power loss, relative to prior art, unloaded loss can reduce greatly.
Accompanying drawing explanation
Fig. 1 show the circuit block diagram of a kind of inverse-excitation type switch power-supply of prior art;
Fig. 2 show the circuit block diagram of a kind of inverse-excitation type switch power-supply according to the present invention;
Fig. 3 show a kind of specific implementation schematic circuit of the load detecting circuit according to the present invention;
Fig. 4 show the working waveform figure of the inverse-excitation type switch power-supply according to the present invention;
Embodiment
Below in conjunction with accompanying drawing, several preferred embodiments of the present invention are described in detail, but the present invention is not restricted to these embodiments. Replacement, amendment, equivalent method and the scheme made are contained in any marrow in the present invention and scope in the present invention. In order to make the public the present invention had and understand thoroughly, the following preferred embodiment of the present invention specifically understands concrete details, and the description not having these details for a person skilled in the art can also understand the present invention completely.
The circuit block diagram of a kind of inverse-excitation type switch power-supply according to the present invention it is shown with reference to figure 2, the present embodiment breaker in middle pipe Q1 is power switch pipe, the switch mode control input terminus of switching tube Q1 transfers to the energy of output terminal, switching tube Q2 is as the synchronous rectification switch of secondary, the switch state of rectifier control circuit 201 trip switch pipe Q2, rectifier control circuit includes synchronous rectification driving circuit 201-1 and synchronous commutating control circuit 201-2, synchronous rectification driving circuit 201-1 directly powers by output voltage, synchronous commutating control circuit 201-2 powers by auxiliary power supply circuit 203.
As shown in Figure 2, described inverse-excitation type switch power-supply also comprises load detecting circuit 202, load detecting circuit 202 specifically comprises voltage sampling circuit 202-1, charge-discharge circuit 202-2 and status signal produce circuit 202-3, voltage sampling circuit 202-1, a kind of specific implementation of charge-discharge circuit 202-2 and status signal generation circuit 202-3 is as shown in Figure 3, described voltage sampling circuit 202-1 comprises sampling hold circuit and comparison circuit, comparison circuit is specially comparer CMP1, described sampling hold circuit is sampled and is kept the voltage between the first power end of described synchronous rectification switch and the 2nd power end, obtain a sampling sustaining voltage Vs, here, described first power end is the drain electrode of switching tube Q2, described 2nd power end is the source electrode of switching tube Q2, and source electrode connects with reference to ground, voltage between the first power end of described comparison circuit more described sampling sustaining voltage Vs and the in real time described synchronous rectification switch of sampling and the 2nd power end and drain-source voltage VDS��
When the voltage compared as comparer CMP1 between the first power end of the described synchronous rectification switch that sampling obtains in real time and the 2nd power end is less than described sampling sustaining voltage Vs, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that declines; When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is greater than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that rises. Comparer CMP1 output is compared signal Vc and is transferred to charge-discharge circuit, and has, as drain-source voltage VDSWhen being less than described sampling sustaining voltage Vs, the described signal Vc that compares is low level state, as drain-source voltage VDSWhen being greater than described sampling sustaining voltage Vs, the described signal Vc that compares is high level state.
Afterwards, the turn-off time of power switch pipe Q1 described in described charge-discharge circuit 202-2 timing, it is specially, described charge-discharge circuit 202-2 comprises the current source Is and electric capacity C1 of series connection, and with the controllable switch S 1 of Capacitance parallel connection, by comparing, signal Vc controls its switch action to controllable switch S 1, compares controllable switch S 1 conducting when signal Vc is high level state, described compare when signal Vc is low level state controlled open S1 disconnect. The both end voltage of charging capacitor is slope voltage Vramp, when described controlled switch disconnects, described slope voltage VrampContinue to rise.
Status signal generation circuit 202-3 specifically comprises a comparer CMP2, and comparer CMP2 receives described slope voltage VrampWith a voltage threshold value V presetth, when described slope voltage rise is to described voltage threshold value, status signal generation circuit produces the status signal of a sign load information, and described status signal transmission gives described synchronous commutating control circuit 201-2. . Generally speaking, user can require to set default time interval according to switch periods and judgement that is unloaded or underloading, such as, default time interval is set to N times of former limit power switch pipe normal operation cycle, such as 4 times, described slope voltage VrampVoltage threshold value V is risen to from zerothTime be the default time interval of turn-off time of described power switch pipe, therefore, described voltage threshold value is set to make slope voltage VrampThe time interval risen meets above-mentioned requirements. When the turn-off time of described power switch pipe reaches described default time interval, then characterize described load and it is in zero load or underloading state.
Can learn from said process, when power switch pipe Q1 disconnects, drain-source voltage VDSStarting decline, compare signal Vc and turn into low level state, therefore, controllable switch S 1 disconnects, and with reason, controllable switch S 1 conducting during power switch pipe Q1 conducting, therefore, the switch state of described controllable switch S 1 is identical with the switch state of described power switch pipe Q1.
Below with reference to the working waveform figure of the inverse-excitation type switch power-supply according to the present invention shown in Fig. 4, as shown in Figure 4, in the t1 moment, be in zero load or underloading state when inverse-excitation type switch power-supply under, then outward current IoutReducing or be zero, former limit circuit enters operating mode of having the hiccups, the switch controlling signal V of former limit power switch pipe Q1gateWaveform as shown in Figure 4, according to the principle of work of inverse-excitation type switch power-supply, when the power switch pipe Q1 on former limit starts conducting, the drain-source voltage V of synchronous rectification switchDSStart to rise, after the complete conducting of power switch pipe Q1, drain-source voltage VDSRemain I �� RDSProduct value, I is the current value by switching tube Q2, RDSFor the conducting resistance of switching tube Q2; When the power switch pipe Q1 on former limit starts to turn off, the drain-source voltage V of synchronous rectification switchDSStart decline, close completely at power switch pipe Q1 and have no progeny, drain-source voltage VDSClose to null value. The drain-source voltage V of secondary synchronous rectification switchDSWaveform as shown in Figure 4. Principle of work according to above-mentioned load detecting circuit, slope voltage VrampThe time risen and switch controlling signal VgateThe low level time corresponding. Until the t2 moment, after the turn-off time of power switch pipe lasts till default time interval, status signal turns into high level, and what judge described inverse-excitation type switch power-supply is in zero load or underloading state. Therefore, by the load detecting circuit of the embodiment of the present invention, the judgement to state of loading can be realized by detecting the drain-source voltage of synchronous rectification switch.
It should be added that, in the present invention, auxiliary power supply circuit 203 comprises with the transformer coupled auxiliary winding in described inverse-excitation type switch power-supply, rectification diode with the first electric capacity. Auxiliary power supply circuit 203 can provide service voltage according to the expectation driving voltage of synchronous commutating control circuit 201-2, such as 5V, in the higher situation of output voltage, such as 12-19V, when zero load or underloading state, the power consumption that synchronous commutating control circuit produces reduces greatly relative to prior art. Those skilled in the art can know by inference, and when output voltage is lower, auxiliary power supply circuit 203 powers to synchronous rectification driving circuit 201-1, and output voltage is powered directly to synchronous commutating control circuit 201-2.
Above-mentioned load detecting circuit judges the state of loading of output terminal by detecting the drain-source voltage change of synchronous rectification switch, it is not necessary to is sampled by output voltage and compares operation, and control program is simple, effective.
The invention also discloses a kind of load detection method being applied in switch power supply, comprise the following steps:
Monitor the voltage between the first power end of the synchronous rectification switch in described inverse-excitation type switch power-supply and the 2nd power end,
Voltage change between the first power end according to described synchronous rectification switch and the 2nd power end judges the switch state of power switch pipe in described inverse-excitation type switch power-supply, wherein,
When described power switch pipe is in shutoff state, and when shutoff state lasts till the default time, then judge that described inverse-excitation type switch power-supply is in zero load or underloading state.
Further, sample and keep the voltage between the first power end of described synchronous rectification switch and the 2nd power end, obtain a sampling sustaining voltage;
When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is less than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that declines;
When voltage between first power end and the 2nd power end of the described synchronous rectification switch obtained of sampling in real time is greater than described sampling sustaining voltage, the voltage judged between the first power end of described synchronous rectification switch and the 2nd power end is in and starts the state that rises.
Further, when the voltage between first power end and the 2nd power end of described synchronous rectification switch starts to rise, characterize described power switch pipe and start conducting;
When voltage between first power end and the 2nd power end of described synchronous rectification switch starts to decline, characterize described power switch pipe and start to turn off.
In sum, the load detecting circuit of the present invention by load detecting circuit to the voltage between the first power end of the synchronous rectification switch in inverse-excitation type switch power-supply and the 2nd power end, to judge the switch state of power switch pipe in described inverse-excitation type switch power-supply accordingly, when described power switch pipe is in shutoff state, and shutoff state is when lasting till default time interval, then judge that the output of described inverse-excitation type switch power-supply is in unloaded or underloading state. In addition, the present invention adopt auxiliary power supply circuit powered by rectifier control circuit, when being in zero load or underloading state when load, synchronous commutating control circuit is powered can be lower, can not producing bigger power loss, relative to prior art, unloaded loss can reduce greatly.
Having carried out detailed description to according to the load detection method of the preferred embodiments of the present invention, detection circuit and the switch power supply of applying it above, those of ordinary skill in the art can know other technologies accordingly by inference or structure and circuit layout, element etc. all can be applicable to described embodiment.
According to embodiments of the invention as described above, these embodiments details that detailed descriptionthe is not all, does not limit the specific embodiment that this invention is only described yet. Obviously, according to above description, can make many modifications and variations. This specification sheets is chosen and is specifically described these embodiments, is the principle in order to explain the present invention better and practical application, thus makes art technician that the present invention and the amendment on basis of the present invention can be utilized well to use. The present invention is only by the restriction of right claim and whole scope and equivalent.