CN102315786A - Single-circuit output flyback converter controlled in current mode - Google Patents

Abstract

The invention relates to a single output flyback converter with current mode control, which includes an AC input source, and the AC input source inputs DC power into the first buffer circuit through an input filter capacitor through a rectifier bridge circuit; the first buffer circuit Connected in parallel to the primary winding of the transformer, the primary winding is connected to the drain of the switch tube, the secondary winding is respectively connected to the output rectifier diode and the input end of the first absorption circuit, the auxiliary winding is connected to the control chip through the chip power supply circuit; the output of the output rectifier diode After the terminal is connected in parallel with the output terminal of the first absorption circuit, it is connected to the three-terminal voltage stabilizing circuit through the output filter capacitor; the second buffer circuit is connected in parallel between the source and drain of the switch tube, and the gate and source are respectively passed through the sampling resistor Connect the control chip; the compensation terminal of the control chip is connected to the output terminal of the isolation circuit, the input terminal of the isolation circuit is connected in parallel with the output filter capacitor, and the other input terminal of the isolation circuit is connected to the three-terminal voltage regulator circuit, and the three-terminal voltage regulator circuit outputs regulated DC power ; There is a second absorbing circuit in the three-terminal voltage stabilizing circuit.

Description

A single output flyback converter with current mode control

technical field

The invention relates to a flyback converter, in particular to a single-output flyback converter used for current mode control in the field of switching power supplies.

Background technique

At present, in the fields of DC motor speed regulation, battery charging, switching power supply, etc., especially in electric traction, electric vehicles such as subways, urban light rails, electric locomotives, trolleybuses, battery cars, and electric forklifts used to use rheostats to realize electric power. The starting, speed regulation and braking of the car have problems such as high power consumption, low efficiency, stepped speed regulation, and poor running stability. After the introduction of DC chopper, electric vehicles are powered by constant DC power supply (such as battery, uncontrolled rectifier power supply), which can conveniently realize stepless speed regulation and stable operation, and more importantly, save electricity by 20% compared with rheostat. 30%, the energy saving effect is huge. However, the use of a linear power supply requires a huge and heavy transformer, and the volume and weight of the filter capacitor required are also quite large, and the voltage feedback circuit works in a linear state, and there is a certain voltage drop on the regulator tube. When outputting a large operating current It will cause the power consumption of the adjustment tube to be too large, the conversion efficiency is low, and a large heat sink must be installed. The switching power supply has the advantages of small size, light weight, simple circuit structure, wide output voltage range, and modularization, but the traditional switching power supply still has the problems of poor commutation effect and low power quality, such as grid operating power Low factor, high switching loss and on-state loss, large transformer leakage inductance and easy to produce intermittent oscillation, low switching frequency, large ripple, insufficient precision of voltage and current stabilization, many harmonic components, poor anti-electromagnetic interference ability and Transformer high-frequency noise and other problems. In addition, BUCK, BOOST, BUCK-BOOST, CUK, SPEIC, ZETA and other non-isolated switching power supplies have poor anti-interference performance and poor load characteristics.

Contents of the invention

In view of the above problems, the purpose of the present invention is to provide a method that can effectively suppress harmonics, reduce losses, reduce ripples, prevent intermittent oscillations, improve the accuracy of voltage and current stabilization, buffer reactive power, reduce electromagnetic susceptibility and electromagnetic interference, and A single-output flyback converter with current-mode control that can increase switching frequency.

In order to achieve the above object, the present invention adopts the following technical solutions: a single output flyback converter with current mode control, characterized in that it includes an AC input source, a rectifier bridge circuit, an input filter capacitor, a first buffer circuit , transformer, switch tube, output rectifier diode, first absorbing circuit, chip power supply circuit, output filter capacitor, three-terminal voltage regulator circuit, second buffer circuit, control chip, isolation circuit and second absorbing circuit; After the AC input source converts AC power into unidirectional DC power through the rectifier bridge circuit, the harmonics in the DC power are filtered by the input filter capacitor and then input into the first buffer circuit; the first buffer The circuit is connected in parallel to the primary winding of the transformer, the primary winding of the transformer is also connected to the drain of the switching tube, and the secondary winding of the transformer is respectively connected to the input end of the output rectifier diode and the first absorption The input end of the circuit, the auxiliary winding of the transformer is connected to the control chip through the chip power supply circuit; after the output end of the output rectifier diode is connected in parallel with the output end of the first absorbing circuit, the output The filter capacitor is connected to the input terminal of the three-terminal voltage stabilizing circuit; the second buffer circuit is connected in parallel between the source and the drain of the switch tube, and the gate and source of the switch tube are respectively sampled The resistance is connected to the control chip; the compensation terminal of the control chip is connected to one output terminal of the isolation circuit, the input terminal of the isolation circuit is connected in parallel with the output filter capacitor, and the other input terminal of the isolation circuit is connected to The input end of the three-terminal voltage stabilizing circuit is output by the three-terminal voltage stabilizing circuit; the three-terminal voltage stabilizing circuit is provided with a device for reducing switching losses in the three-terminal voltage stabilizing circuit and suppressing peak voltage the second snubber circuit.

The transformer is an isolated transformer, which includes a primary winding, a secondary winding and an auxiliary winding. The magnetic core of the transformer is made of soft magnetic materials and a sandwich winding method, and the windings are arranged in parallel with multiple wires, all of which are enameled wire Winding with a safety margin, a reinforced insulation layer is provided between the secondary winding and the auxiliary winding; a dummy load is connected in parallel to the secondary winding of the transformer, and the anode of the output rectifier diode is connected through the dummy load.

Each of the snubber circuits adopts an RCD structure, and the diodes in each of the snubber circuits are FR107 diodes.

The control chip, the switch tube and the isolation circuit form a control circuit, and the control chip adopts a pulse width modulation integrated circuit control chip with a model number of UC3844 without a power switch.

The switch tube adopts a power field effect transistor, and a heat sink is added on the power field effect transistor, and the power field effect transistor and the heat sink are connected through insulating pads and heat dissipation silica gel.

The three-terminal voltage stabilizing circuit includes an adjustable precision shunt regulator and three resistors, the anode of the adjustable precision shunt regulator is sequentially connected in parallel with the first resistor and the second resistor and then connected to the An output filter capacitor, the other end of the second resistor is connected in series with the second resistor and then connected to the reference ground; the cathode of the adjustable precision shunt regulator is connected to the isolation circuit, and the adjustable precision shunt regulator The second absorption circuit composed of a capacitor and a resistor is connected in parallel between the cathode and the reference ground; the model of the adjustable precision shunt regulator is TL431.

The AC input source adopts a single-phase AC power supply provided by an international general industrial frequency AC voltage regulator; the isolation circuit adopts an optocoupler isolation circuit of model TLP521-1.

The present invention has the following advantages due to the adoption of the above technical scheme: 1. The present invention adopts the input single-phase AC power supply provided by the international general power frequency AC voltage regulator because the AC input source is adjustable in voltage, which is convenient to control, and through The fuse is connected with the subsequent rectifier bridge circuit, which improves the safety performance of the whole circuit. Moreover, the rectifier bridge circuit adopts an integrated rectifier bridge, which has a simple structure and good rectification effect, and the output terminal of the rectifier bridge circuit is connected to an input filter capacitor, which further eliminates harmonics. 2. In the present invention, since the input filter capacitor is composed of polar capacitors and ordinary capacitors, the reactive power buffer link and filter link composed of polar capacitors and ordinary capacitors have dual functions of energy storage and filtering, forming a low-impedance power supply internal resistance Features, the DC voltage output by the rectifier bridge circuit is clamped at the power supply voltage level, the surge overvoltage is reduced, and the output DC voltage waveform is close to a rectangle. 3. Since the present invention adopts a snubber circuit connected in parallel with the source and drain of the primary winding of the transformer and the switch tube, the snubber circuit can realize the soft start of power devices, inductors, capacitors and other components, reduce the turn-off loss and absorb Peak current protection transformers and switching tubes and other devices. 4. The transformer of the present invention relatively improves the safety performance of the whole circuit of the present invention due to the isolation transformer. 5. The transformer used in the present invention is equivalent to a plurality of coupled inductors. There will be no current flowing in the primary winding and the secondary winding at the same time, and there is no possibility that the magnetomotive forces will cancel each other out. The continuous conduction mode can greatly reduce the number of winding turns and the size of the magnetic core, and greatly improve the utilization rate of the magnetic core. There is a capacitor between the primary side of the transformer and the positive and negative input power lines of the auxiliary winding, which can provide a low-impedance path for the interference current generated by the switch on and off, thereby reducing the differential mode conduction interference voltage. 6. Due to the flyback circuit structure adopted by the present invention, the distributed capacitance between the conductor and the shielding ground can be greatly reduced, thereby reducing the common-mode conduction current flowing between the power line and the shielding ground; the auxiliary winding of the transformer is grounded , reducing the electromagnetic susceptibility of the control circuit composed of the control chip, the switch tube and the isolation circuit, and greatly improving the electromagnetic compatibility performance of the present invention. 7. In the present invention, since the magnetic core of the transformer adopts soft magnetic materials and the sandwich winding method, the windings are arranged in parallel with multi-strand wires, all of which are wound with enameled wires, leaving a safety margin, and adding There is a reinforced insulation layer, which increases the degree of coupling, greatly reduces the air gap and leakage inductance, as well as core loss and coil loss. 8. The chip power supply circuit used in the present invention is rectified by two stages, which improves the voltage stability, and connects the filter capacitor, which can smooth the voltage ripple and further reduce the harmonic component. The electrolytic capacitor also has an energy storage function, which can ensure The continuous and stable power supply to the control chip, and the current limiting resistor can protect the control chip, which improves the safety performance of the circuit. In addition, the chip power supply circuit is connected in parallel with the auxiliary winding of the transformer, which can improve the potential distribution in the transformer to adjust its internal distributed capacitance, change the impedance of the noise path, and achieve common-mode noise suppression. 9. In the present invention, a false load is added to the secondary winding of the transformer, so that intermittent oscillation can be effectively prevented. 10. The switching tube of the present invention adopts a power field effect transistor, and the power field effect transistor is also provided with a heat sink, which basically solves the influence of temperature changes on the accuracy of voltage and current stabilization. 11. The isolation circuit of the present invention adopts an optocoupler isolation circuit, and the voltage feedback loop formed by the combination of the control chip and the optocoupler isolation circuit can ensure that the fluctuation of the input voltage, the fluctuation of the load, and the fluctuation of the component parameters can be changed by adjusting the current of the control terminal. The duty cycle keeps the output voltage within a certain range. The invention can be widely used in small and medium power occasions, such as DC motor speed regulation, battery charging, switching power supply and other fields, especially in the field of electric traction, such as subways, urban light rails, electric locomotives, trolleybuses, battery cars, electric forklifts and other electric traction. vehicle.

Description of drawings

Fig. 1 is the overall structural representation of the present invention;

Fig. 2 is the implementation schematic diagram of the single output flyback converter of current mode control of the present invention;

Fig. 3 is a schematic structural diagram of a chip power supply circuit of the present invention;

Fig. 4 is the schematic diagram of rectifier bridge circuit structure of the present invention;

Fig. 5 is a structural schematic diagram of the snubber circuit of the present invention, wherein Fig. 5 (a) and Fig. 5 (b) are two RCD structures of the snubber circuit;

Fig. 6 is a schematic structural diagram of an isolation circuit of the present invention;

Fig. 7 is a schematic structural diagram of the three-terminal voltage stabilizing circuit of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figures 1 and 2, the present invention includes an AC input source 1, a rectifier bridge circuit 2, an input filter capacitor 3, a first buffer circuit 4, a transformer 5, a switch tube 6, an output rectifier diode 7, and the first absorption Circuit 8, chip power supply circuit 9, output filter capacitor 10, three-terminal voltage stabilizing circuit 11, second buffer circuit 12, control chip 13, isolation circuit 14 and second absorbing circuit 15.

After the AC input source 1 converts the AC power into unidirectional DC power through the rectifier bridge circuit 2 , the harmonics in the DC power are filtered through the input filter capacitor 3 and then input to the first buffer circuit 4 . The first buffer circuit 4 is connected in parallel to the primary winding of the transformer 5, and the primary winding of the transformer 5 is also connected to the drain of the switching tube 6, and the secondary winding of the transformer 5 is respectively connected to the input terminal of the output rectifier diode 7 and the first The input end of the absorption circuit 8, the auxiliary winding of the transformer 5 is connected to the control chip 13 through the chip power supply circuit 9; after the output end of the output rectifier diode 7 is connected in parallel with the output end of the first absorption circuit 8, it is connected to the output terminal through the output filter capacitor 10. The input end of the three-terminal voltage stabilizing circuit 11 . A second buffer circuit 12 is connected in parallel between the source and drain of the switch tube 6 , and the gate and source of the switch tube 6 are respectively connected to the control chip 13 via a sampling resistor. The compensation end of the control chip 13 is connected to an output end of the isolation circuit 14, the input end of the isolation circuit 14 is connected in parallel with the output filter capacitor 10, and the other input end of the isolation circuit 14 is connected to the input end of the three-terminal voltage stabilizing circuit 11, which is stabilized by the three-terminal Voltage circuit 11 outputs regulated direct current. Wherein, a second absorbing circuit 15 is arranged in the three-terminal voltage stabilizing circuit 11 to reduce switching losses in the three-terminal voltage stabilizing circuit 11 and suppress peak voltage.

The pin Vcc of the control chip 13 is the working power terminal of the integrated block, and the voltage range is 8V-40V. The induction current of the auxiliary winding of the transformer 5 is rectified by the output rectifier diode 7 and filtered by the output filter capacitor 10, and then input to the pin Vcc of the control chip 13 through the current limiting resistor, thereby providing driving power for the control chip 13 and starting the control chip 13 to work normally. The auxiliary winding of the transformer 5 is also connected in parallel with a chip power supply circuit 9 (as shown in Figure 3 ) containing a compensation capacitor, which can make the auxiliary winding of the transformer 5 and the compensation capacitor form a compensation network, improve the structure and connection mode of the transformer 5, and adjust the potential in the transformer 5 distribution, specifically to raise the potential of the shielding layer to adjust the distributed capacitance between the shielding layer and the secondary side, change the impedance of the noise path, and achieve common mode noise suppression; on the other hand, in the case of high frequencies, the auxiliary coil is connected in series in the secondary side loop The noise loop impedance of the secondary side is increased, and the conducted emission is reduced.

In the above-mentioned embodiment, the AC input source 1 adopts a single-phase AC power supply, which is provided by an international general power frequency AC voltage regulator. safety performance.

In the above-mentioned embodiments, as shown in FIG. 4 , the rectifier bridge circuit 2 can convert the alternating current whose level fluctuates around zero into unidirectional direct current through the unidirectional conduction performance of the diode. The rectifier bridge circuit 2 of the present invention adopts an integrated rectifier bridge, and the four diodes of the bridge rectification are packaged together, and only four pins are drawn out, of which two pins 1 and 3 are connected to the AC power supply, and two pins 2 and 4 are connected. The pin outputs unidirectional DC.

In the above-mentioned embodiments, as shown in FIG. 2 , the input filter capacitor 3 is composed of a polar capacitor C1 and a common capacitor C2 connected in parallel. The polar capacitor C1 and the ordinary capacitor C2 are used as energy storage and filter components for reactive power buffering and filtering, forming low-impedance power supply internal resistance characteristics, and clamping the DC voltage output by the rectifier bridge circuit 2 at the power supply voltage level. Reducing the surge overvoltage can make the output DC voltage waveform close to a rectangle.

In the above-mentioned embodiments, in order to protect the transformer 5 and the switch tube 6 from being damaged by the peak current, a first snubber circuit 6 is respectively incorporated between the primary winding of the transformer 5 and the source and drain of the switch tube 6 and the second snubber circuit 12, and the snubber circuit can realize the soft start of power devices, inductors, capacitors and other components. Each snubber circuit adopts RCD structure (as shown in Figure 5). When the power field effect transistor is turned off, if the voltage Vds between the drain and source or the voltage of the primary side of the transformer and the auxiliary winding exceeds the voltage across the capacitor in the snubber circuit When the snubber diode is turned on, the peak current is absorbed by the RCD snubber circuit to reduce the peak current. In addition, the snubber circuit can also reduce the turn-off loss of power electronic devices. The diodes in the first snubber circuit 4 and the second snubber circuit 12 are FR107 diodes, and the snubber capacitors in all snubber circuits are selected to be large enough to ensure that there is no voltage across the snubber capacitors in one switching cycle. Significant changes.

In the above-mentioned embodiments, as shown in Figure 2, the transformer 5 adopts an isolated transformer, which includes a primary winding, a secondary winding and an auxiliary winding, the magnetic core of the transformer 5 adopts a soft magnetic material and a sandwich winding method, and the winding adopts a multi-strand winding. The wires are arranged parallel and wound in parallel, all of which are wound with enameled wires, leaving a safety margin, and a reinforced insulation layer is set between the secondary winding and the auxiliary winding, which increases the coupling degree and greatly reduces the air gap and leakage. Inductance and hysteresis loss, eddy current loss, residual loss and other core loss and loss caused by DC resistance, high-frequency AC loss. The primary winding and the secondary winding of the transformer 5 are used for isolation, the input current is a high-voltage direct current rectified from a single-phase AC power supply, and the output current is a regulated direct current obtained by rectifying and filtering the high-frequency pulse voltage of the secondary winding. The transformer 5 is equivalent to multiple coupled inductors, no current flows in the input and output windings at the same time, and there is no possibility of mutual cancellation of the magnetomotive forces, and the magnetic flux density of its magnetic core depends on the magnitude of the current in the windings. And because the flyback circuit works in the discontinuous conduction mode of the inductor current, the number of winding turns and the size of the magnetic core can be greatly reduced, and the utilization rate of the magnetic core can be greatly improved. Capacitors are connected in parallel between the primary winding of the transformer 5 and the positive and negative input power lines of the auxiliary winding, which can provide a low-impedance path for the interference current generated by the switch on and off, thereby reducing the differential mode conduction interference voltage; The structure of the excitation circuit greatly reduces the distributed capacitance between the conductor and the shielding ground, thereby reducing the common mode conduction current flowing between the power line and the shielding ground. The auxiliary winding of the transformer 5 is grounded, which reduces the electromagnetic susceptibility of the control circuit, which can greatly improve the electromagnetic compatibility performance of the switching power supply. The length of each turn of the wire in the transformer 5 is selected to be as small as possible, and the beginning of the primary side is connected to the drain of the power field effect transistor, which reduces the distributed capacitance of the winding and the coupling degree of the distributed parameters of the adjacent winding, and greatly reduces the power of the transformer 5. ringing noise. A dummy load R15 can also be connected in parallel to the secondary winding of the transformer 5 to prevent the load from opening. When the grid voltage is the highest, the pulse width can be guaranteed to have a certain minimum value without intermittent oscillation. The minimum pulse width is determined by the control chip The minimum conduction ratio of the oscillator in 13 is determined.

The secondary winding of the transformer 5 is connected to the anode of the output rectifying diode 7 through the dummy load R15, and the alternating current output by the secondary winding of the transformer 5 is converted into a unidirectional direct current by utilizing the unidirectional conduction characteristic of the output rectifying diode 7; 7 is connected in parallel with the first absorbing circuit 8 composed of resistor R13 and capacitor C11 in series to reduce the switching loss of the output rectifier diode 7 and suppress the peak voltage that may appear at both ends of the output rectifier diode 7 .

In the above-mentioned embodiments, as shown in FIG. 2, the output filter capacitor 10 is composed of a polar capacitor C9 and a common capacitor C10 connected in parallel. The negative pole of the output rectifier diode 7 is connected to the output filter capacitor 10. The output filter capacitor 10 can further smooth the output rectifier diode. 7 The output DC voltage waveform and stable waveform can reduce harmonic components, optimize output characteristics, and improve the accuracy of voltage and current stabilization. The polar capacitor C9 also has the function of energy storage. The polar capacitor C9 and the ordinary capacitor C10 together form the reactive power buffering link and the filtering link, which has low impedance power supply internal resistance characteristics, so that the output voltage is clamped at the winding voltage level of the secondary winding of the transformer 5, and the surge overvoltage is reduced , the output voltage can be determined, and its waveform is close to a rectangle.

In above-mentioned each embodiment, as shown in Figure 2, control chip 13, switch tube 6 and isolation circuit 14 form control circuit, and wherein control chip 13 adopts the PWM (pulse width modulation) integrated circuit control chip that the model is UC3844 without power switch . The power required by the UC3844 control chip 13 is provided by a multi-channel adjustable output regulated power supply in the prior art. The control circuit adopts the peak current control mode and power electronic devices such as power field effect transistors. The stability of the system is enhanced and the response speed is also accelerated. It can directly reflect the voltage fluctuation caused by interference to the control circuit, and the input voltage disturbance Immunity is improved, dynamic characteristics are improved, and the ability to limit overcurrent. In addition, the fast response speed of the current loop can completely eliminate the 100Hz low-frequency ripple in the output voltage caused by the rectification of the input AC voltage in the separate voltage control mode. Current mode control has good linear adjustment rate and fast input and output dynamic response, overcomes the gain change problem of voltage mode control, and has large signal characteristics, which can optimize the entire feedback link to a first-order circuit and simplify the control loop compensation of the error amplifier Network, greatly improved stability and improved frequency response, with a larger gain-bandwidth product. Inherent pulse-by-pulse current limitation simplifies overload protection and short-circuit protection. It has an automatic magnetic flux balance function, and it is easy to realize automatic current sharing when multiple power supply units are connected in parallel.

Since the drive output part of the control chip 13 acts directly on the gate and source of the switch tube 6 through the sampling resistors R4 and R7 , its compensation terminal is directly connected to the output terminal of the linear optocoupler in the isolation circuit 14 . When the voltage of the current sampling input terminal is greater than 1V, the PWM output will be turned off in order to realize the overcurrent protection of the system, and the voltage drop on the sampling resistor is selected as 0.7V at the maximum peak current of the present invention.

In each of the above-mentioned embodiments, the switching tube 6 adopts a power field effect transistor, and a heat sink is added on the power field effect transistor, and the power field effect transistor and the heat sink are connected by insulating gaskets and heat dissipation silica gel, which can solve the problem of temperature changes. The influence of voltage and current regulation accuracy. The voltage feedback loop formed by the combination of the control chip 13 and the isolation circuit 14 can ensure that the output voltage value can be kept at a certain level by adjusting the current at the control terminal to change the duty cycle for fluctuations in input voltage, load and component parameters. In the range.

In the above embodiments, as shown in FIG. 6 , the isolation circuit 14 can realize the electrical isolation of the control circuit and the transformer 5 and the isolation of the circuit driving circuits of multiple switching devices, so that the circuit has higher safety performance. The isolation circuit 14 of the present invention adopts an optocoupler isolation circuit whose model is TLP521-1. The TLP521-1 optocoupler isolation circuit integrates isolation and drive functions, and the optical signal can be converted into an electrical signal of a triode through a light-emitting diode, thereby controlling The switch signal sent by the circuit is converted into a signal that can turn on and off the switch tube, and is directly connected to the compensation terminal of the control chip 13 to form an optocoupler feedback link to adjust the current of the control terminal to ensure the accuracy of the output voltage. A resistor R8 is connected in series with the anode of the light-emitting diode to the input terminal of the output filter capacitor 10. The resistor R8 can ensure that the optocoupler isolation circuit works in the linear region.

In the above embodiment, as shown in FIG. 7, the three-terminal voltage stabilizing circuit 11 includes an adjustable precision shunt voltage regulator TL431, three resistors R9, R11 and R12, and the anode of the adjustable precision shunt voltage regulator TL431 is sequentially connected in parallel with the resistor R9 The output filter capacitor 10 is connected with R11, and the other end of the resistor R11 is connected with the reference ground after the resistor R12 is connected in series. The cathode of the light-emitting diode in the isolation circuit 14 is connected to the cathode of the adjustable precision shunt regulator TL431, and the second absorption circuit 15 composed of a capacitor C12 and a resistor R10 is connected in parallel between the cathode of the adjustable precision shunt regulator TL431 and the reference ground , Reduce the switching loss of the adjustable precision shunt regulator TL431 and suppress the peak voltage, and use the capacitor C13 to further optimize the waveform. The adjustable precision shunt regulator TL431 has a temperature compensation system and an amplifier inside. It is a voltage reference source with high precision and a three-terminal precision voltage regulator device. Its reference pole can output a 2.5V reference voltage. Resistor R9 can ensure that at least 1mA of continuous current flows into the output pin of the adjustable precision shunt regulator TL431, thus ensuring the normal operation of the adjustable precision shunt regulator TL431. Finally, the reference ground of the adjustable precision shunt regulator TL431 is connected to the DC output port through resistors R11 and R12, and the voltage amplitude of the DC output can be controlled by adjusting the ratio of the resistors R11 and R12.

The above-mentioned embodiments are only used to illustrate the present invention, and the structure and connection mode of each component can be changed. On the basis of the technical solution of the present invention, all improvements to the connection and structure of individual components according to the principles of the present invention and equivalent transformations shall not be excluded from the protection scope of the present invention.

Claims (10)

1. A single output flyback converter of current mode control, characterized in that: it comprises an AC input source, a bridge rectifier circuit, an input filter capacitor, the first buffer circuit, a transformer, a switch tube, an output rectifier diode, The first absorption circuit, chip power supply circuit, output filter capacitor, three-terminal voltage regulator circuit, the second buffer circuit, control chip, isolation circuit and the second absorption circuit; After the AC input source converts AC power into unidirectional DC power through the rectifier bridge circuit, the harmonics in the DC power are filtered by the input filter capacitor and then input into the first buffer circuit; the first A buffer circuit is connected in parallel to the primary winding of the transformer, the primary winding of the transformer is also connected to the drain of the switching tube, and the secondary winding of the transformer is respectively connected to the input end of the output rectifying diode and the first The input end of the first absorbing circuit, the auxiliary winding of the transformer is connected to the control chip through the chip power supply circuit; the output end of the output rectifier diode is connected in parallel with the output end of the first absorbing circuit, and is connected to the control chip through the first absorbing circuit. The output filter capacitor is connected to the input terminal of the three-terminal voltage stabilizing circuit; the second buffer circuit is connected in parallel between the source and the drain of the switch tube, and the gate and source of the switch tube are connected through A sampling resistor is connected to the control chip; the compensation terminal of the control chip is connected to an output terminal of the isolation circuit, the input terminal of the isolation circuit is connected in parallel with the output filter capacitor, and the other input terminal of the isolation circuit terminal is connected to the input end of the three-terminal voltage stabilizing circuit, and the three-terminal voltage stabilizing circuit outputs regulated DC power; voltage to the second sink circuit. 2. The single output flyback converter of a kind of current control as claimed in claim 1, is characterized in that: described transformer adopts isolated transformer, and it comprises primary side winding, secondary side winding and auxiliary winding, so The magnetic core of the above-mentioned transformer adopts soft magnetic material and sandwich winding method, and the windings are arranged in parallel and parallel with multi-strand wires, all of which are wound with enameled wires, leaving a safety margin. Insulation layer; the secondary winding of the transformer is connected in parallel with a dummy load, and connected to the anode of the output rectifier diode through the dummy load. 3. The single output flyback converter of a kind of current control as claimed in claim 1, is characterized in that: each described snubber circuit all adopts RCD structure, and the diode in each described snubber circuit adopts model is FR107 the diode. 4. The single output flyback converter with current mode control as claimed in claim 2, characterized in that: each of the snubber circuits adopts an RCD structure, and the diodes in each of the snubber circuits are FR107 the diode. 5. A current-mode controlled single output flyback converter as claimed in claim 1 or 2 or 3 or 4, characterized in that: said control chip, switch tube and isolation circuit form a control circuit, said The control chip adopts the pulse width modulation integrated circuit control chip of model UC3844 without power switch. 6. A single output flyback converter with current mode control as claimed in claim 1 or 2 or 3 or 4, characterized in that: said switching tube adopts a power field effect transistor, and said power field effect transistor A heat sink is added on the top, and the power field effect transistor and the heat sink are connected through insulating gaskets and heat dissipation silica gel. 7. The single output flyback converter with current mode control as claimed in claim 5, characterized in that: said switching tube adopts a power field effect transistor, and said power field effect transistor is provided with a heat sink , the power field effect transistor and the heat sink are connected through insulating pads and heat dissipation silica gel. 8. A current-mode controlled single output flyback converter as claimed in claim 1 or 2 or 3 or 4 or 7, characterized in that: said three-terminal voltage stabilizing circuit comprises an adjustable precision shunt voltage stabilizing and three resistors, the anode of the adjustable precision shunt regulator is sequentially connected in parallel with the first resistor and the second resistor, and then connected to the output filter capacitor, and the other end of the second resistor is connected in series with the second resistor The two resistors are followed by a reference ground; the cathode of the adjustable precision shunt regulator is connected to the isolation circuit, and a capacitor and a resistor are connected in parallel between the cathode of the adjustable precision shunt regulator and the reference ground. The second absorbing circuit; the model adopted by the adjustable precision shunt regulator is TL431. 9. The single output flyback converter of a current-mode control as claimed in claim 5, wherein the three-terminal voltage stabilizing circuit comprises an adjustable precision shunt voltage regulator and three resistors, and the The anode of the adjustable precision shunt voltage regulator is sequentially connected in parallel with the first resistor and the second resistor and then connected to the output filter capacitor, and the other end of the second resistor is connected in series with the second resistor and then connected to the reference ground; the cathode of the adjustable precision shunt regulator is connected to the isolation circuit, and the second absorption circuit composed of a capacitor and a resistor is connected in parallel between the cathode of the adjustable precision shunt regulator and the reference ground; The model used for the adjustable precision shunt regulator is TL431. 10. A current-mode controlled single output flyback converter according to any one of claims 1 to 9, characterized in that: said AC input source is provided by an international common power frequency AC voltage regulator Single-phase AC power supply; the isolation circuit adopts an optocoupler isolation circuit of model TLP521-1.

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