CN101127487B - Secondary side control power converter - Google Patents

Abstract

The invention relates to a secondary side control power converter, which comprises an input circuit and at least one switching element, wherein the input circuit is provided with a first input end and a second input end; a transformer having a primary winding connected to the switching element and a secondary winding, wherein the voltage variation of the transformer can change the on/off state of the switching element; an output circuit is connected with the secondary side winding of the transformer and is provided with an output end, a controller is arranged on the output circuit, and the controller can sense the output voltage and feed back the output voltage variation to the primary side winding of the transformer correspondingly, so that the primary side winding of the transformer can correspondingly operate the control switch element to perform PWM or PFM switching operation so as to control the output voltage.

Description

Secondary Control Power Converter

technical field

The invention relates to a power converter, in particular to a secondary-side controlled power converter, which can control the on and off actions of switching elements on the primary side of a transformer.

Background technique

Switching power converters have the characteristics of high efficiency and small size, and are currently widely used in various electronic devices. As shown in Figure 11, it is one of the circuit structures of conventional flyback converters, and its circuit structure is mainly It has an input circuit 1', a transformer T1', an output circuit 2', and an optocoupler 3', and the input circuit 1' is connected to the input power supply Vin, and mainly has a switching transistor Q1', a controller 11', and the transistor Q1 'connect the primary side winding of the transformer T1', and the controller 11' can be used for PWM control, and the output terminal is connected to the transistor Q1', and the input terminal FB is connected to the end of the optocoupler 3'; and the output circuit 2' is connected to the transformer T1' The secondary side winding, and its output terminal voltage Vout are connected in parallel with the other end of the optocoupler 3', so that the optocoupler 3' isolates the input circuit 1' from the output circuit 2', and feeds back the output power supply Vout to the input circuit 1 'The controller 11', so that the controller 11' can control the switching transistor Q1' to stabilize the output voltage corresponding to the output.

The output voltage stability of the aforementioned circuit must be controlled by the feedback of the optocoupler 3', but the characteristics of the optocoupler 3' will directly affect the stability and reliability of the system, for example, the coupling efficiency of the optocoupler 3' will directly It affects the accuracy of the output voltage Vout, and if the optocoupler 3' is used as a charger (not shown in the figure), the constant current function must add additional components to compensate for the instability of the optocoupler, which will increase the circuit cost and be relatively expensive. Multiple components cause a large loss in standby loss.

Figure 12 shows another conventional flyback converter circuit architecture, which mainly has an input circuit 5', a transformer T2', and an output circuit 6', and its input circuit 5' is connected to the input power supply Vin, and has a switching transistor Q2 ', controller 51', and the transistor Q2' is connected to the first winding N1' on the primary side of the transformer T2', and the output end of the controller 51' is connected to the transistor Q2', and the input end is connected to the second winding on the primary side of the transformer T2' N2', and the controller 51' is a PWM controller; and the output circuit 6' is connected to the secondary side third winding N3' of the transformer T2', and has an output terminal voltage Vout, so that the controller 51' senses the voltage generated by the transformer T2 The 'secondary side feeds back the voltage change of the primary side winding of the transformer T2', and controls the transistor Q2' to turn on and off correspondingly to control the output terminal voltage Vout.

Although the above-mentioned circuit has the most concise components, because the controller 51' does not directly sense the output terminal voltage, it directly depends on the characteristic sensing control of the transformer T2', and the feedback voltage is discontinuous, resulting in the stability and reliability of the circuit system. Poor, no-load output voltage stability is poor, dynamic voltage regulation performance is poor and missing.

Contents of the invention

The purpose of the present invention is to provide a control power converter on the secondary side, so that the operation of the switching element on the primary side of the transformer has better accuracy and reliability.

In order to achieve the above object, the present invention adopts the following technical solutions: a secondary side control power converter, comprising: an input circuit with at least one switching element; a transformer, the primary winding of which is connected to the aforementioned switching element, and its voltage changes It can change the on and off state of the switching element, and has a secondary side winding; an output circuit, connected to the secondary side winding of the transformer, and has an output terminal, and the aforementioned circuit can transfer the input energy of the input circuit to the output circuit through the transformer to generate The output terminal voltage, and a controller is set in the output circuit, and the controller can sense the output voltage, and can perform actions to affect the primary side winding of the transformer in response to the change of the sensed output voltage, so that the primary side winding of the transformer can control the switching element correspondingly For PWM or PFM switching action to control the output voltage, the output circuit has a rectifier diode, and a capacitor is connected in parallel at the output end to ground, and the input end of the controller of the output circuit is connected to the output end power supply, and the first and second control ends of the control device are across The two terminals of the rectifier diode are connected, and the controller decides to make three state changes between the first and second control terminals: connection of resistive load, short circuit and open circuit.

The combination of the above input circuit, transformer and output circuit is a self-excited flyback converter circuit architecture.

The primary side of the above-mentioned transformer has a first winding and a second winding with the same polarity, and the secondary side has a third winding with opposite polarity to the aforementioned first and second windings, and the input circuit has a starting circuit, and its input terminal is connected to the input The power supply, the input end of the start-up circuit, one end of the first winding on the primary side of the transformer, and the output end of the start-up circuit are connected to the B pole of the first transistor, and the C pole of the first transistor is connected to the other end of the aforementioned first winding, and the first transistor is The switching element; one end of the second winding on the primary side of the transformer is connected to the resistor and the B pole of the first transistor, and the other end of the second winding is grounded; and the emitter of the first transistor is connected to the resistor to ground.

The above-mentioned first transistor is connected to the current limiting protection circuit.

The above-mentioned current limiting protection circuit has a second transistor, and the B pole of the second transistor is connected to the emitter of the first transistor, and the C pole is connected to the B pole of the first transistor, and the emitter is grounded.

The above-mentioned diodes are located at the output end.

The above-mentioned diodes are located at the ground terminal.

When the voltage at the output terminal exceeds the set voltage, the controller controls the first and second control terminals to connect the resistive load from the time when the energy of the transformer T is completely transferred to the output terminal to the time before the first transistor starts up again, and prevents the first The transistor is energized again and then turned off, putting the circuit in stop mode.

The first side of the transformer has a first winding and a second winding with the same polarity, and the secondary side has a third winding with opposite polarity to the aforementioned first and second windings, and when the voltage at the above-mentioned output terminal is insufficient, the controller controls the first and second windings. The second control terminal is short-circuited for a short time, and the capacitor energy of the output circuit is stored in the third winding, and then the controller controls the first and second control terminals to be disconnected, and the energy of the second winding restarts the first transistor conduction. Pass.

A secondary-side control power converter, comprising: a transformer, the primary side has a first winding and a second winding with the same polarity, and the secondary side has a third winding with opposite polarity to the first and second windings ; An input circuit with a start-up circuit, and its input end is connected to the input power supply, the start-up circuit input end, and one end of the first winding on the primary side of the transformer, and the start-up circuit output end is connected to the first transistor B pole, and the first transistor C The pole is connected to the other end of the aforementioned first winding; one end of the second winding on the primary side of the transformer is connected to a resistor, and the resistor is connected to the B pole of the first transistor, and the other end of the second winding is grounded; and the emitter of the first transistor is connected to The resistance is grounded, and the first transistor is connected to the second transistor, and the B pole of the second transistor is connected to the first transistor emitter, and the C pole is connected to the first transistor B pole, and its emitter is grounded; an output circuit with a rectifier Diode, and a capacitor connected in parallel at the output end is grounded, and the output circuit is equipped with a controller, and the input end of the controller is connected to the power supply of the output end, and the first and second control ends of the controller are connected across the two ends of the diode; and the controller can sense Measure the output voltage, and feed back to the primary side winding of the transformer corresponding to the change of the sensed output voltage, so that the primary side winding of the transformer can control the first transistor to perform PWM or PFM switching action to control the output voltage; the above-mentioned first and second Between the two control terminals, the controller decides to make three state changes: connection of resistive load, short circuit and open circuit.

The above-mentioned diodes are located at the output end.

The above-mentioned diodes are located at the ground terminal.

When the voltage at the above output terminal exceeds the set voltage, the controller controls the first and second control terminals to connect the resistive load from the time when the energy of the transformer T is completely transferred to the output terminal to the time before the first transistor restarts, and prevents the first transistor from reactivating. Excitation conducts and then breaks, putting the circuit in stop mode.

When the above-mentioned output terminal voltage is insufficient, the controller controls the short circuit between the first and second control terminals for a short time, and makes the capacitor energy of the output circuit store in the third winding, and then makes the controller control the first and second control terminals to open the circuit, and the second The energy of the second winding restarts the conduction of the first transistor.

Using the above scheme, the present invention mainly transfers the input energy of the input circuit to the output circuit through the transformer to generate the output terminal voltage, and sets a controller in the output circuit, and the controller can sense the output voltage and can sense the output voltage. The action performed by the change of voltage, such as the three state changes of connecting resistive load, short circuit, and open circuit, is determined by the controller, so as to affect the primary side winding of the transformer, so that the primary side winding of the transformer can control the switching element for PWM or PFM according to the action. Switching action to control the output voltage; thus, the present invention controls the action of the switching element on the primary side through the secondary side controller to be more accurate and reliable, and does not require an optical coupling element, which can reduce costs and make the circuit more stable and have a longer service life It is longer and has the function of synchronous rectification.

Description of drawings

Fig. 1 is a schematic diagram of the circuit structure of the present invention;

Fig. 2 is the circuit schematic diagram of the first embodiment of the present invention;

3 is a schematic diagram of voltage and current points of the first embodiment of the present invention;

FIG. 4 is a schematic diagram of the action waveform corresponding to FIG. 3 in the first embodiment of the present invention;

Fig. 5 is a schematic diagram of the action of the controller in stop mode when the output terminal voltage is too large in the first embodiment of the present invention;

Fig. 6 is a schematic diagram of the operation of the controller's secondary side start mode when the voltage at the output terminal is insufficient in the first embodiment of the present invention;

Fig. 7 is a schematic diagram of the action of the controller when the voltage at the output terminal is insufficient in the first embodiment of the present invention;

Fig. 8 is a schematic diagram of the action waveforms of the secondary side cycle stop mode and start mode corresponding to Fig. 5, Fig. 6 and Fig. 7 according to the first embodiment of the present invention;

FIG. 9 is a schematic diagram of the waveform of the current limiting protection function of the second transistor in the first embodiment of the present invention;

Fig. 10 is a schematic circuit diagram of the second embodiment of the present invention;

11 is a schematic diagram of a conventional flyback converter circuit with an optical coupling element;

FIG. 12 is a schematic diagram of another conventional flyback converter circuit.

Explanation of main component symbols

Detailed ways

The circuit framework of the present invention has an input circuit, a transformer, and an output circuit, and the input end of the input circuit is connected to the input power supply, the output side is connected to the transformer, and at least one switching element is provided; the primary side winding of the transformer is connected to the aforementioned switching element , and its voltage change can change the on and off state of the switching element, and has a secondary side winding; and the output circuit is connected to the secondary side winding of the transformer, and has an output terminal, and the aforementioned circuit can transfer the input energy of the input circuit to the The output circuit generates the output terminal voltage, and a controller is installed in the output circuit, and the controller can sense the change of the output terminal voltage and feed it back to the primary side winding of the transformer, so that the primary side winding of the transformer can control the switching element for PWM or PFM according to the action. mode switching action to control the output voltage.

A more specific circuit of the present invention can be a self-excited flyback circuit structure, wherein the primary side of the transformer has a first winding and a second winding with the same polarity, and the secondary side has a polarity opposite to the first and second windings. The third winding, the input end of the input circuit is connected to the input power supply, the input end of the start-up circuit, and one end of the first winding on the primary side of the transformer, and the output end of the start-up circuit is connected to the first transistor B pole of the switching element, and the first transistor C One end of the second winding on the primary side of the transformer is connected to the resistor and the B pole of the first transistor, and the other end of the second winding is grounded; and the emitter of the first transistor is connected to the resistor ground; and The current limiting protection circuit is connected to the first transistor, and the current limiting protection circuit has a second transistor, and the B pole of the second transistor is connected to the emitter of the first transistor, and the C pole is connected to the B pole of the first transistor, and the second transistor The emitter of the diode is grounded; the output circuit has a rectifier diode, and its anode is connected to the third winding of the transformer, and the other end of the third winding is grounded, and the cathode of the diode is connected to the output terminal, and a capacitor is connected in parallel to the output terminal, and the output The circuit is equipped with a controller, and the controller is connected to the power supply of the output terminal, and the input terminal of the controller is connected to the contact point of the voltage dividing resistor connected in series with the output terminal, and has an error amplifier and a reference voltage to compare the voltage change of the output terminal, and the controller has the first 1. The second control terminal is connected across the two terminals of the diode, and the first and second control terminals are determined by the controller to perform three state changes: connection of resistive load, short circuit, and open circuit. The controller on the primary side controls the action of the switching element on the primary side to have better accuracy and reliability, and because there is no optical coupling element, the cost, circuit stability, and life can be reduced, and the synchronous rectification function can be added.

Please refer to Fig. 1, the main circuit structure of the present invention has an input circuit 1, a transformer T, an output circuit 2, and the input end of this input circuit 1 is connected to the input power supply Vin, the output side is connected to the transformer T, and has at least one switch Element 11, and this switching element 11 can be individual or combined element of transistor, MOSFET or other switch function; And the primary side winding of transformer T is connected with aforementioned switching element 11, and its voltage change can change switching element 11 on and off state, It also has a secondary side winding; and the output circuit 2 is connected to the secondary side winding of the transformer T and has an output terminal, and the aforementioned circuit can transfer the input energy of the input circuit 1 from the transformer T to the output terminal of the output circuit 2 to generate an output terminal voltage Vout, and a controller 21 is set in the output circuit 2, and the controller 21 can sense the change of the output terminal voltage Vout and feed it back to the primary side winding of the transformer, so that the primary side winding of the transformer T can control the switching element 11 for PWM or PFM switching action to control the output terminal voltage.

Please refer to Fig. 2, the more specific circuit of the first embodiment of the present invention is a self-excited flyback converter circuit architecture, wherein the primary side of the transformer T has a first winding N1, a second winding N2 with the same polarity, and a secondary winding N2 with the same polarity. The side has a third winding N3 opposite in polarity to the aforementioned first and second windings N1 and N2, and the input end of the input circuit 1 is connected to the input power supply Vin, the input end of the starting circuit 12, and one end of the first winding N1 on the primary side of the transformer T, In addition, the output end of the starting circuit 12 is connected to the pole of the first transistor Q1B of the switching element, and the pole of the first transistor Q1C is connected to the other end of the first winding N1; The B pole of the first transistor Q1, and the other end of the second winding N2 is grounded; the emitter of the first transistor Q1 is connected to the resistor RS grounded; and the first transistor Q1 is connected to a current limiting protection circuit, and the current limiting protection circuit has a second current limiting protection circuit. Two transistors Q2, the B pole of the second transistor Q2 is connected to the emitter of the first transistor Q1, the C pole is connected to the B pole of the first transistor Q1, and the emitter is grounded.

The output circuit 2 has a rectifier diode D1 located at the output end, and its anode is connected to the third winding N3 of the transformer T, and the other end of the third winding N3 is grounded, and the cathode of the diode D1 is connected to the output end and connected in parallel to the output end The capacitor C1 is grounded, and the output circuit 2 is provided with a controller 21 with a power supply VDD and a ground GND contact, and the VDD contact of the controller 21 is connected to the output power supply Vout, and the input terminal FB of the controller 21 is connected to the branch connected in series by the output terminal. Piezoresistive contacts, and an error amplifier, a reference voltage (not shown in the figure) to compare the output voltage change, and the controller 21 has power supply VDD, ground GND contacts, and the first and second control terminals CTL1, CTL2 are bridged The two terminals of the diode D1, and between the first and second control terminals CTL1 and CTL2 are determined by the controller 21 to be connected to a resistive load, short-circuited, or open-circuited.

Please refer to FIG. 3 and FIG. 4 together. When the present invention operates, the input terminal of the input circuit 1 inputs the operating voltage Vin, and the starting circuit 12 outputs the pulse a to the first transistor Q1, so that the first transistor Q1 is turned on Ton, and has The collector current Ic, and at this time the input current is grounded through the first winding N1 of the transformer T, the first transistor Q1, and the resistor RS, and part of the current is grounded through the second winding N2 of the transformer T, the first transistor Q1, and the resistor RS, and At this time, the polarity above the first winding N1 and the second winding N2 is positive, and the polarity above the third winding N3 is negative; and when the first transistor Q1 is connected in series with the resistor RS, the voltage rises and the second transistor Q2 is turned on. Q1 is turned off, and transfers the energy from the primary side of the transformer T to the secondary side, and reverses the polarity of the third winding N3 on the secondary side, so that the current can flow through the diode D1 to generate the output terminal voltage Vout, and there is a current Id, And when the energy of the third winding N3 is fully released, the polarity of the transformer T turns, and the energy stored in the parasitic inductance of the second winding N2 of the transformer T can make the first transistor Q1 conduction again, so that the present invention has automatic soft start and The ringing self-excited structure works in a discontinuous mode, and the start circuit 12 does not operate and consume power after the first start, and the start pulse will be sent again after the system stops for more than a preset time or the reset condition is met .

The controller 21 of the present invention can sense the change of the output terminal voltage Vout for control, please refer to Fig. 3, Fig. 5, Fig. 7 and Fig. 8 together, the controller 21 of the present invention can control The first and second control terminals CTL1 and CTL2 are connected to a resistive load from the time when the energy of the transformer T is completely transferred to the output terminal to the time before the first transistor Q1 starts up again, so that the resistive load can consume the leakage current of the transformer T when Id is zero The residual energy is sensed, and its current direction is shown in the direction of the arrow in Figure 5, and prevents the first transistor Q1 from being excited and turned on again, and then returns to the off-circuit state shown in Figure 7, making the circuit in stop mode, preventing the output terminal voltage Vout from continuously increasing to achieve Constant voltage effect.

Please refer to Fig. 6 and Fig. 8, when the output terminal voltage Vout is insufficient in the present invention, the controller 12 can control the short circuit between the first and second control terminals CTL1 and CTL2 for a short time, and store the energy of the capacitor C1 of the output circuit 2 to the first Three windings N3, and Id can drop correspondingly; As shown in Fig. 7 and Fig. 8, let the controller 21 control the first and second control terminals CTL1, CTL2 to be disconnected, the energy will reduce the voltage of Vsw, and transfer to the first The energy of the second winding N2 restarts the conduction of the first transistor Q1, so that the circuit enters the self-excited switching operation again, and the energy of the input circuit 1 can be quickly transferred to the output circuit 2, and the output terminal voltage Vout is increased to achieve a constant voltage function. Therefore, the controller 21 on the secondary side of the transformer T in the present invention can make the first transistor Q1 on the primary side of the transformer T perform PWM or PFM action so that the output terminal voltage Vout has a constant voltage function, and the controller 21 of the present invention directly Sensing the output terminal voltage Vout can have high precision and high efficiency, synchronous rectification function, and better reliability, and the present invention does not require optical coupling elements, and can have better life and reliability.

Please refer to Fig. 3 and Fig. 9. In the present invention, if the output circuit 2 (such as diode D1) on the secondary side of the transformer T is short-circuited or overloaded so that the current Ic of the first winding N1 on the primary side of the transformer T increases rapidly, the resistance RS on the input circuit 1 The voltage Vsense will turn on the second transistor Q2, and turn off the first transistor Q1 to stop the circuit system, and when the situation is eliminated, the circuit system will be activated by the startup circuit 12, so that the second transistor Q2 can be used as a limiter. flow protection.

In addition, when the output circuit 2 is short-circuited, the controller 2 can also stop the first and second control terminals CTL1 and CTL2 for a long time, and wait for the start-up circuit 12 to reset until the short circuit is released.

In addition, although the present invention has the start-up circuit 12, the cost of the start-up circuit 12 is low, and the power consumption is low, so the present invention can have the function of low cost and high efficiency.

Please refer to Fig. 10, the circuit of the second embodiment of the present invention is substantially the same as that of the first embodiment, the difference lies in that the rectifier diode D1 of the output circuit 2 is arranged at the contact point and the ground terminal under the third winding, and its polarity direction is the same as that of the first embodiment. One embodiment is the opposite, and this circuit can also have the same self-excited switching function as the first embodiment, and the control levels of the first and second control terminals CTL1 and CTL2 of the controller 21 can be matched and changed to have the same control function, And this circuit can add synchronous rectification function to the controller to improve efficiency.

The aforementioned embodiments are for clearly describing the features of the present invention, and are not intended to limit the patent scope of the present invention. The present invention can be changed and modified within the spirit and scope of the present invention.

Claims (14)

1. secondary side control power converter comprises:

One input circuit, tool one switch element at least;

One transformer, its first side winding connects aforementioned switches element, and its change in voltage can change switch element open and close state, and the tool secondary side winding;

One output circuit, connect the Circuit Fault on Secondary Transformer winding, and tool output, and aforementioned circuit can be passed to output circuit generation output end voltage via transformer with the intake of input circuit, in output circuit controller is set again, but this controller sensing output voltage, and can change the first side winding that the execution action influences transformer at the sensing output voltage, but make the first side winding respective action control switch element of transformer do PWM or PFM switch motion with control output voltage, output circuit tool rectifier diode, and in output shunt capacitor ground connection, the controller input of output circuit connects output end power again, this controling appliance first again, these rectifier diode two ends of the second control end cross-over connection, and make first by controller decision, connect resistive load between second control end, short circuit, three kinds of state variation open circuit.

2. secondary side control power converter as claimed in claim 1 is characterized in that: input circuit, transformer, output circuit are combined as self-excitation direction flyback converter circuit framework.

3. secondary side control power converter as claimed in claim 1, it is characterized in that: first winding that transformer primary side tool polarity is identical, second winding, the secondary side tool and the opposite tertiary winding of aforementioned first and second winding polarity, input circuit tool start-up circuit again, and its input connects first winding, one end of input power supply, start-up circuit input, transformer primary side, this start-up circuit output connects the first transistor B utmost point again, and this first transistor C utmost point connects the aforementioned first winding other end, and this first transistor is described switch element again; Second winding, one end of this transformer primary side connects the resistance and the first transistor B utmost point, this second winding other end ground connection again; The emitter-base bandgap grading of this first transistor connects grounding through resistance again.

4. secondary side control power converter as claimed in claim 3 is characterized in that: the first transistor connects a current-limiting protection circuit.

5. secondary side control power converter as claimed in claim 4 is characterized in that: current-limiting protection circuit tool transistor seconds, the B utmost point of this transistor seconds connects the first transistor emitter-base bandgap grading, and the C utmost point connection the first transistor B utmost point, and its emitter grounding.

6. secondary side control power converter as claimed in claim 5, it is characterized in that: diode is located at output end position.

7. secondary side control power converter as claimed in claim 5 is characterized in that: diode is located at the earth terminal position.

8. secondary side control power converter as claimed in claim 5, it is characterized in that: controller was controlled first, second control end and is connected resistive load in the time that transformer T energy is transferred to before output time to described the first transistor starts once more fully when output end voltage exceeded setting voltage, and stop the first transistor to excite conducting once more, be off state then, making circuit is stop mode.

9. secondary side control power converter as claimed in claim 5, it is characterized in that: first winding, second winding that the transformer first side tool polarity is identical, otherwise secondary side tool and aforementioned first, second winding polarity be the tertiary winding mutually, controller was controlled between first, second control end one blink of short circuit when output end voltage was not enough again, and the capacitor energy that makes output circuit is stored to the tertiary winding and makes controller control first, second control end again opening circuit, and the energy of second winding is restarted described the first transistor conducting.

10. secondary side control power converter is characterized in that: includes,

One transformer, first winding that primary side tool polarity is identical, second winding, the secondary side tool and the opposite tertiary winding of aforementioned first, second winding polarity; One input circuit, the tool start-up circuit, and its input connects first winding, one end of input power supply, start-up circuit input, transformer primary side, and this start-up circuit output connects the first transistor B utmost point again, and this first transistor C utmost point connects the aforementioned first winding other end; Second winding, one end of this transformer primary side connects resistance again, and this resistance connection the first transistor B utmost point, and this second winding other end ground connection; The emitter-base bandgap grading of this first transistor connects grounding through resistance again, connects transistor seconds in the first transistor again, and the B utmost point of this transistor seconds connection the first transistor emitter-base bandgap grading, and the C utmost point connection the first transistor B utmost point, and its emitter grounding; One output circuit, the tool rectifier diode, and in output shunt capacitor ground connection, output circuit is provided with controller again, and the controller input connects output end power, first, second control end cross-over connection diode two ends of this controling appliance again; But and this controller sensing output voltage, and can be corresponding the sensing output voltage change and feedback to the transformer first side winding, but make the first side winding respective action control the first transistor of transformer do PWM or PFM switch motion with control output voltage; Between this first, second control end by controller decision connect resistive load, short circuit, three kinds of state variation open circuit.

11. secondary side control power converter as claimed in claim 10 is characterized in that: diode is located at output end position.

12. secondary side control power converter as claimed in claim 10 is characterized in that: diode is located at the earth terminal position.

13. secondary side control power converter as claimed in claim 10, it is characterized in that: controller was controlled first, second control end and is connected resistive load in the time that transformer T energy is transferred to before output time to the first transistor starts once more fully when output end voltage exceeded setting voltage, and stop the first transistor to excite conducting once more, be off state then, making circuit is stop mode.

14. secondary side control power converter as claimed in claim 10, it is characterized in that: controller was controlled between first, second control end one blink of short circuit when output end voltage was not enough, and the capacitor energy that makes output circuit is stored to the tertiary winding and makes controller control first, second control end again opening circuit, and the energy of second winding is restarted the first transistor conducting.

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