CN103747560A - Feedback control circuit for switch power supply - Google Patents

Abstract

The invention discloses a feedback control circuit for a switch power supply. The feedback control circuit comprises an inductance energy storage circuit and a peak value current comparator connected with the inductance energy storage circuit. The peak value current comparator comprises an operational amplifier, an RS trigger, a falling edge detection circuit and a driving circuit. The output end of the operational amplifier is connected with the S end of the RS trigger; the falling edge detection circuit is connected with the R end of the RS trigger; the Q end of the RS trigger is connected with the input end of the driving circuit; the output end of the driving circuit, the falling edge detection circuit, and the same-phase input end of the operational amplifier are connected with the inductance energy storage circuit; the driving circuit comprises two series-connected inverters; the falling edge detection circuit comprises a buffer, a capacitor and a comparator; the buffer, the capacitor and the comparator are successively connected; and the capacitor is connected with the inverting input end of the comparator. The advantages are as follows: the circuit structure is simple, and a feedback control principle is utilized so that the control of an LED is stable, the control precision is high, and the load regulation rate is high.

Description

A kind of feedback control circuit for Switching Power Supply

Technical field

The present invention relates to integrated circuit fields, relate in particular a kind of feedback control circuit for Switching Power Supply.

Background technology

Because global environmental protection consciousness progressively improves, LED illuminating product obtains exploitation energetically, and starts to come into gradually huge numbers of families in recent years.In LED illuminating product, the LED driving power circuit of AC-DC provides power supply for LED, and due to LED(Light Emitting Diode) be current mode device, luminosity is subject to current affects larger, and therefore LED driving power need to provide stable constant current output for LED.

During driving, current LED mains lighting supply extensively adopt critical current conduction mode (BCM) and cutout control model (DCM) to realize constant current output control.In order to realize higher power-efficient, some power drives chips have adopted quasi-resonance control model, a kind of control model between BCM and DCM.

This according to different current conduction mode and the system topology adopting, need different control chips to adopt various constant current algorithm and circuit to realize output constant current.Circuit structure load, has increased the cycle that chip is researched and developed; These open loop constant current control methods make low precision, the problems such as poor line regulation and load regulation.

Summary of the invention

The invention provides a kind of feedback control circuit for Switching Power Supply, its circuit structure is simple, utilizes feedback control principle, makes the control of LED stablize, and control precision is high, and the regulation of load is high.

For solving above-mentioned technical problem, the present invention by the following technical solutions:

A kind of feedback control circuit for Switching Power Supply, it comprises inductive energy storage circuit and is connected to the peak current comparator on inductive energy storage circuit, described peak current comparator comprises operational amplifier, rest-set flip-flop, trailing edge testing circuit and drive circuit, the output of described operational amplifier is connected on the S end of rest-set flip-flop, described trailing edge testing circuit is connected on the R end of rest-set flip-flop, the Q end of rest-set flip-flop is connected on the input of drive circuit, the output of described drive circuit, trailing edge testing circuit, the in-phase input end of operational amplifier is all connected on inductive energy storage circuit, described drive circuit comprises the inverter of two series connection, described trailing edge testing circuit comprises buffer, electric capacity and comparator, described buffer, electric capacity is connected successively with comparator, described electric capacity is connected on the reverse input end of comparator.

Further technical scheme is:

Described inductive energy storage circuit comprises full-wave rectification bridge and be connected to the transformer on full-wave rectification bridge, and one end of the first former limit Np of described transformer is connected on the output of full-wave rectification bridge, and the other end is connected with the source electrode of field effect transistor Q1; One end ground connection on the second former limit of described transformer, is in series with resistance R _ f h and resistance R _ f l on the other end, the common port of described resistance R _ f h and resistance R _ f l is connected on trailing edge testing circuit; One end ground connection of the secondary of described transformer, the other end is connected on the anode of diode D, between the described negative electrode of diode D and the earth terminal of secondary, is connected with capacitor C out; The grid of described field effect transistor Q1 is connected on the output of drive circuit, and the drain electrode of field effect transistor Q1 is connected to the ground by resistance R cs, and the drain electrode of described field effect transistor Q1 is connected on the in-phase input end of operational amplifier.

Compared with prior art, the invention has the beneficial effects as follows:

1, the present invention utilizes feedback control principle to control LED, makes the control precision of LED highly, and load is that the regulation of LED is high.

2, circuit structure of the present invention is simple, integrated simple, can reduce the chip R&D cycle.

Accompanying drawing explanation

Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.

Fig. 1 is circuit diagram of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further illustrated.Embodiments of the present invention include but not limited to the following example.

[embodiment 1]

A kind of feedback control circuit for Switching Power Supply as shown in Figure 1, it comprises inductive energy storage circuit and is connected to the peak current comparator on inductive energy storage circuit, described peak current comparator comprises operational amplifier, rest-set flip-flop, trailing edge testing circuit and drive circuit, the output of described operational amplifier is connected on the S end of rest-set flip-flop, described trailing edge testing circuit is connected on the R end of rest-set flip-flop, the Q end of rest-set flip-flop is connected on the input of drive circuit, the output of described drive circuit, trailing edge testing circuit, the in-phase input end of operational amplifier is all connected on inductive energy storage circuit, described drive circuit comprises the inverter of two series connection, described trailing edge testing circuit comprises buffer, electric capacity and comparator, described buffer, electric capacity is connected successively with comparator, described electric capacity is connected on the inverting input of comparator.

Load is connected on inductive energy storage circuit, inputs a constant voltage on the inverting input of operational amplifier.Utilize trailing edge testing circuit to detect the signal of inductive energy storage circuit, utilize inductive energy storage circuit to produce the reference voltage of operational amplifier, by rest-set flip-flop, remove to trigger drive circuit inductive energy storage circuit is driven.Peak current comparator can detect resonance time, utilizes feedback control principle to control inductive energy storage circuit, and its circuit theory is simple, improves control precision and regulation to load.

[embodiment 2]

Described inductive energy storage circuit comprises full-wave rectification bridge and be connected to the transformer on full-wave rectification bridge, and one end of the first former limit Np of described transformer is connected on the output of full-wave rectification bridge, and the other end is connected with the source electrode of field effect transistor Q1; One end ground connection on the second former limit of described transformer, is in series with resistance R _ f h and resistance R _ f l on the other end, the common port of described resistance R _ f h and resistance R _ f l is connected on trailing edge testing circuit; One end ground connection of the secondary of described transformer, the other end is connected on the anode of diode D, between the described negative electrode of diode D and the earth terminal of secondary, is connected with capacitor C out; The grid of described field effect transistor Q1 is connected on the output of drive circuit, and the drain electrode of field effect transistor Q1 is connected to the ground by resistance R cs, and the drain electrode of described field effect transistor Q1 is connected on the in-phase input end of operational amplifier.

Operation principle of the present invention is as follows:

It is upper that load is connected in parallel on capacitor C out, inputs a constant voltage on the inverting input of operational amplifier.This circuit can detect resonance time, in conjunction with former limit Continuity signal, can obtain current lead-through Toff and the Ton time of secondary Ns accurately.The reference voltage of operational amplifier is produced by the resistance R cs of inductive energy storage circuit, utilizes rest-set flip-flop by drive circuit, cut-offfing of field effect transistor Q1 to be controlled.Whole circuit adopts the principle of feedback, can effectively improve the control precision to load.

Be as mentioned above embodiments of the invention.The present invention is not limited to above-mentioned execution mode, and anyone should learn the structural change of making under enlightenment of the present invention, and every have identical or close technical scheme with the present invention, within all falling into protection scope of the present invention.

Claims (2)

1. the feedback control circuit for Switching Power Supply, it is characterized in that: it comprises inductive energy storage circuit and is connected to the peak current comparator on inductive energy storage circuit, described peak current comparator comprises operational amplifier, rest-set flip-flop, trailing edge testing circuit and drive circuit, the output of described operational amplifier is connected on the S end of rest-set flip-flop, described trailing edge testing circuit is connected on the R end of rest-set flip-flop, the Q end of rest-set flip-flop is connected on the input of drive circuit, the output of described drive circuit, trailing edge testing circuit, the in-phase input end of operational amplifier is all connected on inductive energy storage circuit, described drive circuit comprises the inverter of two series connection, described trailing edge testing circuit comprises buffer, electric capacity and comparator, described buffer, electric capacity is connected successively with comparator, described electric capacity is connected on the reverse input end of comparator.

2. a kind of feedback control circuit for Switching Power Supply according to claim 1, it is characterized in that: described inductive energy storage circuit comprises full-wave rectification bridge and is connected to the transformer on full-wave rectification bridge, one end of the first former limit Np of described transformer is connected on the output of full-wave rectification bridge, and the other end is connected with the source electrode of field effect transistor Q1; One end ground connection on the second former limit of described transformer, is in series with resistance R _ f h and resistance R _ f l on the other end, the common port of described resistance R _ f h and resistance R _ f l is connected on trailing edge testing circuit; One end ground connection of the secondary of described transformer, the other end is connected on the anode of diode D, between the described negative electrode of diode D and the earth terminal of secondary, is connected with capacitor C out; The grid of described field effect transistor Q1 is connected on the output of drive circuit, and the drain electrode of field effect transistor Q1 is connected to the ground by resistance R cs, and the drain electrode of described field effect transistor Q1 is connected on the in-phase input end of operational amplifier.

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