阅读说明：本技术 一种反激变换器输出电流估算电路及其使用装置 (Flyback converter output current estimation circuit and using device thereof ) 是由 谢小高 张佳豪 于 2021-07-16 设计创作，主要内容包括：本发明提出一种无需原边采样电阻的反激变换器输出电流估算电路,通过对变压器绕组电压进行积分、处理和滤波,即可在变压器原边侧估算出输出电流信息,进而实现输出恒流。本发明省去了原边采样电阻,降低变换器复杂性及损耗,可适用于临界断续或断续的反激变换器或者非隔离的buckboost变换器。(The invention provides an output current estimation circuit of a flyback converter without a primary sampling resistor, which can estimate output current information on the primary side of a transformer by integrating, processing and filtering the voltage of a winding of the transformer so as to output a constant current. The invention saves a primary sampling resistor, reduces the complexity and the loss of the converter, and is suitable for a critical discontinuous or discontinuous flyback converter or a non-isolated buck boost converter.)

1. A flyback converter output current estimation circuit, comprising: the switch integrating circuit, the switch control signal generating circuit and the filter circuit;

the switch integrating circuit comprises: an integrating circuit and switch S1; the switch S1 is connected in parallel with an integrating capacitor in an integrating circuit, the switching integrating circuit receives voltage information at two ends of the transformer winding Wt, and the switch S1 receives a control signal VG _ S1 generated by a switching control signal generating circuit and outputs a triangular wave signal Vs;

the switch control signal generating circuit generates a control signal VG _ S1 of a switch S1 according to voltage information at two ends of a transformer winding Wt, the switching frequency of the control signal VG _ S1 is consistent with the switching frequency of a primary side switching tube of the flyback converter, and the low level interval of the control signal is the same as the follow current interval of a secondary side rectifying tube of the flyback converter;

the filter circuit receives the triangular wave signal Vs output by the switch integrating circuit, filters the triangular wave signal Vs and outputs a voltage signal Vio _ est reflecting the output current information of the flyback converter.

2. The flyback converter output current estimation circuit of claim 1, wherein the integration circuit is a passive integration circuit formed by a resistor R3 and an integrating capacitor C1;

one end of the resistor R3 is connected with the different-name end of the transformer winding Wt, the other end of the resistor R3 is connected with one end of the integrating capacitor C1, the other end of the integrating capacitor C1 is connected with the same-name end of the transformer winding Wt and the control ground, the integrating capacitor C1 is connected with the switch S1 in parallel, and the triangular wave signal Vs is output from the connection point of the resistor R3 and the integrating capacitor C1.

3. The flyback converter output current estimation circuit of claim 1, wherein the switch control signal generation circuit comprises: a voltage division network consisting of a resistor R1 and a resistor R2, a comparator Uc1 and a reference voltage Vref; one end of the resistor R1 is connected with the different-name end of the transformer winding Wt, the other end of the resistor R1 is connected with one end of the capacitor R2 and the negative input end of the comparator Uc1, the other end of the resistor R2 is connected with the same-name end of the transformer winding Wt, the positive input end of the comparator Uc1 is connected with the reference voltage Vref, and the output end of the comparator Uc1 outputs a control signal VG _ S1.

4. The flyback converter output current estimation circuit of claim 3 wherein the reference voltage Vref is a fixed voltage value.

5. The output current estimation circuit of the flyback converter as claimed in claim 1, wherein the filter circuit is an RC filter formed by a resistor R4 and a capacitor C2, one end of the resistor R4 receives the triangular wave signal Vs output by the switch integrator circuit, the other end of the resistor R4 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to a control ground, and the connection point of the resistor R4 and the capacitor C2 outputs a dc voltage signal Vio _ est reflecting the output current information of the flyback converter.

6. The flyback converter output current estimation circuit of claim 1, wherein the flyback converter output current estimation circuit further comprises: an amplifying circuit; the input end of the amplifying circuit is electrically connected with the output end of the switch integrating circuit, the output end of the amplifying circuit is electrically connected with the input end of the filter circuit, and the amplifying circuit amplifies the triangular wave signal Vs output by the switch integrating circuit.

7. The flyback converter output current estimation circuit of claim 1, wherein the flyback converter output current estimation circuit further comprises: a follower circuit; the input end of the following circuit is electrically connected with the output end of the switch integrating circuit, the following circuit is electrically connected with the input end of the filter circuit, and the following circuit follows the triangular wave signal Vs output by the switch integrating circuit.

8. A primary side constant current control device applied to the flyback converter output current estimation circuit according to claim 1, comprising: the flyback converter comprises a flyback converter output current estimation circuit, a quasi-single-stage flyback converter and a constant current control circuit;

the quasi-single-stage flyback converter comprises: the circuit comprises an input rectifier bridge B1, an input capacitor Cin, diodes D1-D4, an inductor L1, a transformer T, a bus capacitor Cbus, a primary side switch tube Q1, a secondary side rectifier tube Do and an output capacitor Co;

two input ends of the input rectifier bridge B1 are connected with two ends of an input alternating current voltage source Vac, a positive output end of the input rectifier bridge is connected with one end of an input capacitor Cin, one end of an inductor L1 and an anode of a diode D1, the other end of the inductor L1 is connected with a cathode of a diode D2 and an anode of a diode D3, a cathode of a diode D3 is connected with one end of a primary side switch tube Q1, an anode of the diode D4 and a synonym end of a primary side winding of the transformer T, a cathode of a diode D4 is connected with a cathode of the diode D1, a positive end of a bus capacitor Cbus and a synonym end of the primary side winding of the transformer T, a negative end of the bus capacitor Cbus, the other end of a primary side switch tube Q1, an anode of the diode D2, the other end of the input capacitor Cin and a negative output end of the input rectifier bridge B1 are connected with a control ground, a synonym end of a synonym rectifier of a secondary side winding of the transformer T is connected with an anode of a secondary side rectifier tube Do, a cathode of a secondary side rectifier tube Do is connected with an output capacitor Co, the negative end of the output capacitor Co is connected with the dotted end of the secondary winding of the transformer T; one input end of the flyback converter output current estimation circuit is connected with the synonym end of the auxiliary winding Wt of the transformer T, the other input end of the flyback converter output current estimation circuit and the synonym end of the auxiliary winding Wt of the transformer T are connected with a control ground, the output end of the flyback converter output current estimation circuit is connected with one input end of the constant current control circuit, and the output end of the constant current control circuit outputs a driving signal VGS of a primary side switching tube Q1;

the constant current control circuit compares a received voltage signal Vio _ est reflecting the output current information of the flyback converter with an internal constant current reference, and after an error between the voltage signal Vio _ est and the internal constant current reference is amplified, a generated driving signal VGS of a primary side switching tube Q1 is modulated to control the output current of the quasi-single-stage flyback converter to be constant.

9. The primary side constant current control device as claimed in claim 8, wherein the filter in the flyback converter output current estimation circuit is a filter in an integration network of a multiplexing error amplifier.

Technical Field

The invention relates to a switching power supply technology in the technical field of power electronics, in particular to an output current estimation circuit without a primary sampling resistor, which is suitable for a flyback converter.

Background

With the rapid development of power electronic technology application, people have increasingly high requirements on the small size, high efficiency and high reliability of the switching converter. Meanwhile, for safety, the input and output terminals of the transformer are usually electrically isolated to avoid electric shock due to faults. The flyback converter topology is characterized in that an isolation transformer is added on the basis of a Buck-Boost topology, so that the electrical isolation of input and output is realized, and multi-path output can be easily realized by adding a secondary winding and a circuit. In addition, the topological structure is simple, the number of components is small, the control is easy, and the like, so that the method is widely applied to medium and small power switching power supplies.

For applications such as constant current charging of an LED driving power supply or a storage battery, accurate constant current control of a load is required. According to different output current sampling modes, a control framework of the constant current type flyback converter can be divided into primary side feedback control and secondary side feedback control. The secondary feedback control generally directly samples the output current, and then is used for realizing the isolation between the control circuit and the output through an optical coupler or other isolation devices. However, due to the introduction of the optocoupler or other isolation devices, the cost and complexity of the control circuit are inevitably increased, and the reliability of the system is greatly reduced while the cost of the system is increased. The method adopts a primary side feedback control mode, and output current information is calculated by sampling a primary side current signal of the isolation converter through a sampling resistor, so that the accuracy and the stability of the output current are realized. The primary side feedback control mode can ensure the accuracy of output current, and simultaneously, removes isolation devices such as an optical coupler and the like, simplifies the complexity of a system peripheral control circuit, and reduces the system volume and the cost.

A schematic block diagram of a primary constant current flyback converter implemented based on a primary side serially connected with a sampling resistor is shown in fig. 1, where a module 101 is a primary constant current control chip. Although the acquisition mode of the current change information of the primary winding is simple to implement, the loss caused by the sampling resistor can reduce the efficiency of the whole system, and the precision of the sampling resistor can influence the precision of the output constant current.

Therefore, how to acquire the information of the output current of the flyback transformer without connecting a sampling resistor in series on the primary side and eliminate the loss caused by connecting the sampling resistor in series on the primary side is a work with practical significance and challenge.

Disclosure of Invention

Aiming at the problems existing when the flyback converter adopts primary side constant current control, the invention provides the output current estimation circuit of the flyback converter, which can estimate the output current information on the primary side of the transformer without sampling the primary side current by a primary side sampling resistor, thereby realizing the output constant current.

Specifically, a flyback converter output current estimation circuit includes: the switch integrating circuit, the switch control signal generating circuit and the filter circuit;

the switch integrating circuit comprises: an integrating circuit and switch S1; the switch S1 is connected in parallel with an integrating capacitor in an integrating circuit, the switching integrating circuit receives voltage information at two ends of the transformer winding Wt, and the switch S1 receives a control signal VG _ S1 generated by a switching control signal generating circuit and outputs a triangular wave signal Vs;

the switch control signal generating circuit generates a control signal VG _ S1 of a switch S1 according to voltage information at two ends of a transformer winding Wt, the switching frequency of the control signal VG _ S1 is consistent with the switching frequency of a primary side switching tube of the flyback converter, and the low level interval of the control signal is the same as the follow current interval of a secondary side rectifying tube of the flyback converter;

the filter circuit receives the triangular wave signal Vs output by the switch integrating circuit, filters the triangular wave signal Vs and outputs a voltage signal Vio _ est reflecting the output current information of the flyback converter.

Preferably, the integration circuit is a passive integration circuit formed by a resistor R3 and an integration capacitor C1;

one end of the resistor R3 is connected with the different-name end of the transformer winding Wt, the other end of the resistor R3 is connected with one end of the integrating capacitor C1, the other end of the integrating capacitor C1 is connected with the same-name end of the transformer winding Wt and the control ground, the integrating capacitor C1 is connected with the switch S1 in parallel, and the triangular wave signal Vs is output from the connection point of the resistor R3 and the integrating capacitor C1.

Preferably, the switch control signal generating circuit includes: a voltage division network consisting of a resistor R1 and a resistor R2, a comparator Uc1 and a reference voltage Vref; one end of the resistor R1 is connected with the different-name end of the transformer winding Wt, the other end of the resistor R1 is connected with one end of the capacitor R2 and the negative input end of the comparator Uc1, the other end of the resistor R2 is connected with the same-name end of the transformer winding Wt, the positive input end of the comparator Uc1 is connected with the reference voltage Vref, and the output end of the comparator Uc1 outputs a control signal VG _ S1.

Preferably, the reference voltage Vref is a fixed voltage value. The reference voltage Vref is a voltage generated from a winding voltage of the transformer winding Wt.

Preferably, the filter circuit is an RC filter formed by a resistor R4 and a capacitor C2, one end of the resistor R4 receives the triangular wave signal Vs output by the switch integrator circuit, the other end of the resistor R4 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to a control ground, and a connection point of the resistor R4 and the capacitor C2 outputs a dc voltage signal Vio _ est reflecting the output current information of the flyback converter.

Preferably, the flyback converter output current estimation circuit further includes: an amplifying circuit; the input end of the amplifying circuit is electrically connected with the output end of the switch integrating circuit, the output end of the amplifying circuit is electrically connected with the input end of the filter circuit, and the amplifying circuit amplifies the triangular wave signal Vs output by the switch integrating circuit.

Preferably, the flyback converter output current estimation circuit further includes: a follower circuit; the input end of the following circuit is electrically connected with the output end of the switch integrating circuit, the following circuit is electrically connected with the input end of the filter circuit, and the following circuit follows the triangular wave signal Vs output by the switch integrating circuit.

A primary side constant current control device comprising: the flyback converter, the constant current control circuit and the flyback converter output current estimation circuit;

the flyback converter comprises a primary side switching tube Q1, a transformer T, a secondary side rectifying tube Do and an output capacitor Co; the primary side switching tube Q1 is a single semiconductor element or a composite switching tube formed by a plurality of semiconductor elements; one end of a primary side switch tube Q1 is connected with the positive end of an input voltage Vin, the other end of the primary side switch tube Q1 is connected with a control ground and the dotted end of a primary side winding Wt of a transformer T, the dotted end of the primary side winding Wt of the transformer T is connected with the negative end of the input voltage Vin, the dotted end of a secondary side winding of the transformer T is connected with the anode of a secondary side rectifier tube Do, the cathode of the secondary side rectifier tube Do is connected with the positive end of an output capacitor Co, and the negative end of the output capacitor Co is connected with the dotted end of the secondary side winding of the transformer T; one input end of the output current estimation circuit of the flyback converter is connected with the synonym end of the primary winding Wt of the transformer T, the other input end of the output current estimation circuit of the flyback converter is connected with a control ground, the output end of the output current estimation circuit of the flyback converter is connected with the input end of the constant current control circuit, and the output end of the constant current control circuit outputs a driving signal VGS of a primary side switching tube Q1;

the constant current control circuit compares a received voltage signal Vio _ est reflecting the output current information of the flyback converter with an internal constant current reference, and after an error between the voltage signal Vio _ est and the internal constant current reference is amplified, a generated driving signal VGS of the primary side switching tube Q1 is modulated to control the output current of the flyback converter to be constant.

A primary side constant current control device comprising: the flyback converter comprises a flyback converter output current estimation circuit, a quasi-single-stage flyback converter and a constant current control circuit;

the quasi-single-stage flyback converter comprises: the circuit comprises an input rectifier bridge B1, an input capacitor Cin, diodes D1-D4, an inductor L1, a transformer T, a bus capacitor Cbus, a primary side switch tube Q1, a secondary side rectifier tube Do and an output capacitor Co;

two input ends of the input rectifier bridge B1 are connected with two ends of an input alternating current voltage source Vac, a positive output end of the input rectifier bridge is connected with one end of an input capacitor Cin, one end of an inductor L1 and an anode of a diode D1, the other end of the inductor L1 is connected with a cathode of a diode D2 and an anode of a diode D3, a cathode of a diode D3 is connected with one end of a primary side switch tube Q1, an anode of the diode D4 and a synonym end of a primary side winding of the transformer T, a cathode of a diode D4 is connected with a cathode of the diode D1, a positive end of a bus capacitor Cbus and a synonym end of the primary side winding of the transformer T, a negative end of the bus capacitor Cbus, the other end of a primary side switch tube Q1, an anode of the diode D2, the other end of the input capacitor Cin and a negative output end of the input rectifier bridge B1 are connected with a control ground, a synonym end of a synonym rectifier of a secondary side winding of the transformer T is connected with an anode of a secondary side rectifier tube Do, a cathode of a secondary side rectifier tube Do is connected with an output capacitor Co, the negative end of the output capacitor Co is connected with the dotted end of the secondary winding of the transformer T; one input end of the flyback converter output current estimation circuit is connected with the synonym end of the auxiliary winding Wt of the transformer T, the other input end of the flyback converter output current estimation circuit and the synonym end of the auxiliary winding Wt of the transformer T are connected with a control ground, the output end of the flyback converter output current estimation circuit is connected with one input end of the constant current control circuit, and the output end of the constant current control circuit outputs a driving signal VGS of a primary side switching tube Q1;

the constant current control circuit compares a received voltage signal Vio _ est reflecting the output current information of the flyback converter with an internal constant current reference, and after an error between the voltage signal Vio _ est and the internal constant current reference is amplified, a generated driving signal VGS of a primary side switching tube Q1 is modulated to control the output current of the quasi-single-stage flyback converter to be constant.

Preferably, the filter in the output current estimation circuit of the flyback converter is a filter in which an integrating network of the multiplexing error amplifier is used.

The invention has the beneficial effects that: the circuit of the invention can estimate the output current information on the primary side of the transformer by integrating, processing and filtering the voltage of the winding of the transformer without sampling the primary current by the primary sampling resistor, thereby realizing the output of constant current, saving the primary sampling resistor and reducing the complexity and the loss of the converter. The invention is suitable for critical discontinuous or discontinuous flyback converters or non-isolated buck-boost converters.

Drawings

Fig. 1 is a basic schematic block diagram of a primary side constant current flyback converter with a primary side sampling resistor;

fig. 2 shows an output current estimation circuit of a flyback converter according to the present invention;

fig. 3 is a key waveform diagram of the output current estimation circuit of the flyback converter according to the present invention;

fig. 4 shows a specific embodiment of a primary side constant current flyback converter formed based on the output current estimation circuit of the flyback converter proposed by the present invention;

fig. 5 shows a specific embodiment of a quasi-single-stage primary-side constant current flyback converter formed based on the output current estimation circuit of the flyback converter proposed by the present invention;

in the figure: 101. the device comprises a primary side constant current control chip 100, a flyback converter output current estimation circuit 1001, a switch integration circuit 1002, a switch pulse generation circuit 1003, a filter circuit 200 and a constant current control circuit.

Detailed Description

In order that the manner in which the features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

Fig. 2 shows a flyback converter output current estimation circuit of the present invention. The flyback converter output current estimation circuit 100 of the present invention includes: a switching integration circuit 1001, a switching pulse generation circuit 1002, and a filter circuit 1003. Wherein the content of the first and second substances,

the switched integrator circuit 1001 includes an integrator circuit including a resistor R3 and an integrating capacitor C1, and a switch S1. One end of the resistor R3 is connected with the different-name end of the transformer winding Wt, the other end of the resistor R3 is connected with one end of the integrating capacitor C1, the other end of the integrating capacitor C1 is connected with the same-name end of the transformer winding Wt and the control ground, the integrating capacitor C1 is connected with the switch S1 in parallel, and the triangular wave signal Vs is output from the connection point of the resistor R3 and the integrating capacitor C1.

The switch control signal generating circuit 1002 includes a voltage dividing network formed by a resistor R1 and a resistor R2, and a comparator Uc 1. One end of the resistor R1 is connected with the different name end of the transformer winding Wt, the other end of the resistor R1 is connected with one end of the resistor R2 and the negative input end of the comparator Uc1, the other end of the resistor R2 is connected with the same name end of the transformer winding Wt, and the positive input end of the comparator Uc1 is connected with the reference voltage Vref.

The filter circuit 1003 receives the triangular wave signal Vs output by the switching integrator circuit 1001, filters the triangular wave signal Vs, and outputs a voltage signal Vio _ est reflecting the output current information of the flyback converter.

Fig. 3 shows a key waveform diagram of the output current estimation circuit of the flyback converter of the present invention, and for convenience of explanation, the main waveforms of the flyback converter when operating in the current interruption mode are also shown in the diagram. Wherein VGS Is a driving waveform of a primary switching transistor Q1 of the flyback converter, Ip Is a primary current waveform, Ip-pk Is a primary current peak value, Is a secondary rectifier current waveform, Is-pk Is a secondary rectifier current peak value, Vwt Is a transformer winding waveform, Vs-pk Is a peak value of a triangular wave signal Vs output by the switching integrator circuit 1001, Io Is an output current, Ton Is a primary switching transistor on-time, Toff Is a primary switching transistor off-time, and Toff1 Is a secondary rectifier freewheeling time.

Suppose the number of turns of the primary winding of the flyback converter is Np, the number of turns of the secondary winding is Ns, the number of turns of the transformer winding Wt is Nt, and the primary excitation inductance of the transformer is Lp. When the flyback converter works in an intermittent or critical intermittent state, the current peak value Is-pk of the secondary rectifier tube of the transformer can be calculated as follows:

wherein, V_OFor the flyback converter output voltage, Toff1 is the secondary rectifier freewheel time.

Design R₃，C₁The parameters should satisfy:

R₃＞＞1/2πf_sC₁ (2)

when the switching frequency of the control signal VG _ S1 is the same as the switching frequency of the primary side switching tube of the flyback converter, and the low level section of the control signal is the same as the freewheeling section of the secondary side rectifying tube of the flyback converter, the peak value Vs-pk of the triangular wave signal Vs output by the switch integrator circuit 1001 can be determined as:

vwt is the amplitude of the transformer winding Wt in the freewheeling interval of the secondary rectifier tube of the flyback converter. Simultaneous (1) and (3) can result in:

as can be seen from (4), when the parameters of the flyback converter circuit and the parameters of the switching integrator circuit 1001 are both determined, Vs-pk Is linearly proportional to Is-pk. The waveform of the secondary rectifier current is and the waveform of the triangular wave signal Vs output by the switch integrator circuit 1001 are both right triangles and have the same width, so the average value of the two is also in linear proportion, that is, the average value of Vs and Io are in linear proportion. Therefore, the output current estimation circuit of the flyback converter can estimate the output current value. Further, the voltage signal Vio _ est filtered by the filter 1003 is sent to the constant current control circuit, so that primary side constant current control can be realized.

Fig. 4 shows a schematic diagram of the flyback converter primary side constant current control device formed by the output current estimation circuit of the flyback converter, the flyback converter and the constant current control circuit 200 according to the present invention.

Referring to fig. 4, the flyback converter includes a primary switching tube Q1, a transformer T, a secondary rectifier Do, and an output capacitor Co. The primary side switching tube Q1 may be a single semiconductor element or a composite switching tube formed by a plurality of semiconductor elements. One end of a primary side switch tube Q1 is connected with the positive end of an input voltage Vin, the other end of the primary side switch tube Q1 is connected with a control ground and the dotted end of a primary side winding Wt of a transformer T, the dotted end of the primary side winding Wt of the transformer T is connected with the negative end of the input voltage Vin, the dotted end of a secondary side winding of the transformer T is connected with the anode of a secondary side rectifier tube Do, the cathode of the secondary side rectifier tube Do is connected with the positive end of an output capacitor Co, and the negative end of the output capacitor Co is connected with the dotted end of the secondary side winding of the transformer T; one input end of the output current estimation circuit 100 of the flyback converter is connected with the synonym end of the primary winding Wt of the transformer T, the other input end of the output current estimation circuit 100 of the flyback converter is connected with a control ground, the output end of the output current estimation circuit 100 of the flyback converter is connected with one input end of the constant current control circuit 200, and the output end of the constant current control circuit 200 outputs a driving signal VGS of the primary switching tube Q1. The constant current control circuit 200 compares the received voltage signal Vio _ est reflecting the output current information of the flyback converter with an internal constant current reference, and after the error between the voltage signal Vio _ est and the internal constant current reference is amplified, the generated driving signal VGS of the primary side switching tube Q1 is modulated to control the output current of the flyback converter to be constant. The constant current control circuit is prior art in the field and will not be described in detail here.

Fig. 5 shows a schematic diagram of a primary side constant current control device of a quasi-single-stage flyback converter, which is formed by the output current estimation circuit of the flyback converter of the present invention, and a quasi-single-stage flyback converter and constant current control circuit 200.

Referring to fig. 5, the quasi-single-stage flyback converter includes an input rectifier bridge B1, an input capacitor Cin, diodes D1-D4, an inductor L1, a transformer T, a bus capacitor Cbus, a primary switch tube Q1, a secondary rectifier tube Do, and an output capacitor Co. Two input ends of the input rectifier bridge B1 are connected with two ends of an input alternating current voltage source Vac, a positive output end of the input rectifier bridge is connected with one end of an input capacitor Cin, one end of an inductor L1 and an anode of a diode D1, the other end of the inductor L1 is connected with a cathode of a diode D2 and an anode of a diode D3, a cathode of a diode D3 is connected with one end of a primary side switch tube Q1, an anode of the diode D4 and a synonym end of a primary side winding of the transformer T, a cathode of a diode D4 is connected with a cathode of the diode D1, a positive end of a bus capacitor Cbus and a synonym end of the primary side winding of the transformer T, a negative end of the bus capacitor Cbus, the other end of a primary side switch tube Q1, an anode of the diode D2, the other end of the input capacitor Cin and a negative output end of the input rectifier bridge B1 are connected with a control ground, a synonym end of a synonym rectifier of a secondary side winding of the transformer T is connected with an anode of a secondary side rectifier tube Do, a cathode of a secondary side rectifier tube Do is connected with an output capacitor Co, the negative end of the output capacitor Co is connected with the dotted end of the secondary winding of the transformer T; one input end of the flyback converter output current estimation circuit 100 is connected with the different-name end of the auxiliary winding Wt of the transformer T, the other input end of the flyback converter output current estimation circuit 100 and the same-name end of the auxiliary winding Wt of the transformer T are connected with a control ground, the output end of the flyback converter output current estimation circuit 100 is connected with one input end of the constant current control circuit 200, and the output end of the constant current control circuit 200 outputs a driving signal VGS of the primary side switching tube Q1. The constant current control circuit 200 compares the received voltage signal Vio _ est reflecting the output current information of the flyback converter with an internal constant current reference, and after the error between the voltage signal Vio _ est and the internal constant current reference is amplified, the generated driving signal VGS of the primary side switching tube Q1 is modulated to control the output current of the quasi-single-stage flyback converter to be constant.

The output current estimation circuit of the flyback converter can also form a constant current device with a non-isolated buck-boost converter, the principle of the constant current device is basically the same as the realization principle of the primary side constant current device of the flyback converter, and the detailed description is omitted here.

The claims of the present invention are primarily intended to define and protect the proposed main circuit structure. The invention is intended to cover alternatives, modifications, equivalents, and alternatives which may be included within the spirit and scope of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed. The details of the above circuit configuration and its control may be varied accordingly in its practical implementation, while still being encompassed by the present invention.

As noted above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to certain specific characteristics, features, or aspects of the invention with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification, unless the above detailed description section explicitly defines such terms. Accordingly, the actual scope of the invention encompasses not only the disclosed embodiments, but also within the claims.