TWI382643B - With synchronous control of the return-type circuit - Google Patents

Description

Flyback circuit with synchronous control

A flyback circuit with synchronous control, in particular, a circuit for controlling synchronization of the secondary side and the primary side by a synchronization signal.

Most electrical devices today work to achieve a stable current, and all need to obtain local power through a power supply and convert it into DC or AC power output. The power supply includes a wide range of converters, including converters. Inverters, etc., one of which is called a Flyback Converter. In the power supply circuit, the use of the flyback converter can achieve the advantages of simple design and low price; the characteristic of the flyback converter is that the primary side coil of the transformer for converting power in the circuit is opposite in polarity to the secondary side coil. And when the input current passes through the primary side coil, the secondary side coil usually uses a diode or a switching element to block current conduction, and stores energy in the transformer, and when the primary side coil is turned off, the diode is automatically caused by The polarity of the induced potential of the secondary side coil is reversed and turned on, or the current of the secondary side coil is circulated by turning on the switching element; and in order to improve efficiency, the current flyback converter is usually controlled by a switching element. The release of the energy of the secondary side coil, however, the switching element needs to be triggered by the control signal to be turned on and off, so that subsequent circuit creation for controlling the switching element is performed.

U.S. Patent No. 7,233,505, "High efficiency flyback converter with primary, secondary, and electrical windings", wherein the flyback converter includes a primary side (which can be turned into a primary side) and a secondary a side (which may be turned into a secondary side) having a primary winding (12) and a secondary winding (22), respectively, and a tertiary winding (23) sensing a polarity change of the secondary winding, wherein the secondary side is turned off or turned on Controlled by a MOSFET (reference numeral 25), the action of the MOSFET is controlled by the signal induced by the tertiary winding, in other words, the created MOSFET synchronous action is generated by the self-excitation of the secondary side; another similar creation US Patent No. 6424544 "continuous mode flyback converter" in which the converter includes a primary winding (101) and a secondary winding. (107) and an auxiliary winding (108), which senses the polarity change of the primary winding by the auxiliary winding to generate a signal to control the operation of the transistor (110), so the prior patent also uses the secondary side self-excited way to reach two The function of the secondary side synchronous opening and closing; only the aforementioned flyback type self-excited synchronous control still has a defect, basically the self-excited signal is intercepted from the polarity change of the primary side coil, and the polarity change of the secondary side coil is derived from The current fluctuation of the primary side coil, in other words, the secondary side coil starts to react after the polarity of the primary side coil changes, so that the effect of zero voltage switching (ZVS) cannot be achieved, and switching loss is naturally generated; When the primary side coil is switched between light load, short circuit or other abnormal state, the secondary side coil cannot sense the polarity change, that is, the secondary side coil induced potential does not change with the primary side polarity change. The self-excited control mechanism will lose its regularity. At that time, the self-excited frequency will be extremely irregular due to many factors such as load impedance, circuit body impedance and so on. It is difficult to predict that this will cause an extremely turbulent power waveform on the secondary side that will destroy the flyback converter.

Therefore, the control technology of the conventional self-excited flyback converter still needs to be improved to avoid runaway and circuit damage in the above abnormal state.

In view of the fact that the control technology of the conventional self-excited flyback converter has the risk of losing control when abnormal, and the secondary side cannot be synchronized with the primary side in advance, the present invention provides a secondary side that is matched once by the synchronization signal. The side can synchronize the action of the flyback circuit and limit the length of its minimum self-excited period to avoid the self-excited runaway problem of the flyback circuit.

The present invention is a flyback type circuit with synchronous control, wherein one of the secondary side and the secondary side respectively have a primary side coil and a secondary side coil of opposite polarity, wherein the current conduction period of the secondary side coil is affected by Controlling the opening and closing of a synchronous rectification switch, the flyback circuit further includes a pulse width modulation unit, a synchronization control unit and a conduction period limiting unit, wherein the pulse width modulation unit generates a driving signal to control the primary side The current conduction period of the coil, and before generating the driving signal, first provide an output timing to lead the synchronization signal of the driving signal, and the synchronous control unit obtains the synchronization signal through an induction coil group, and drives the synchronous rectification switch with the synchronization signal Off, and the on-period limiting unit starts a period limit timing after the synchronous rectification switch is turned on, and the synchronous rectification switch is continuously turned on At the end of the period limit timing, the on period limiting unit generates a forcing off signal to turn off the conduction of the synchronous rectification switch, and after the synchronous rectification switch is turned off, the on period limiting unit is reset back to the initial state, thereby controlling the mode Maintain the minimum operating frequency of the flyback circuit operation.

With the above circuit structure, the secondary side of the flyback circuit can achieve the effect of zero voltage switching (ZVS) by synchronizing the synchronization signal with the primary side, and when the primary side is suspended or an abnormality occurs, the conduction is performed. The cycle limiting unit automatically maintains the lowest operating frequency to avoid self-excited runaway of the flyback circuit.

The invention is a flyback circuit with synchronous control. Please refer to FIG. 1 and FIG. 2, which is a flyback circuit. The transformer 1 in the circuit can be divided into a primary side and a secondary side. The transformer 1 One of the secondary sides has a primary side coil 11 and a secondary side coil 12 opposite in polarity, and the current conduction period of the secondary side coil 12 is controlled by the opening and closing of a synchronous rectifier switch 5, and The current conduction period of the primary side coil 11 is controlled by a pulse width modulation unit 3, which generates a driving signal (V _G1 ) to drive the opening and closing of a power switch 4, thereby controlling the primary side. coil current conduction cycle 11, the other, the pulse width modulation unit 3 is further to generate the driving signal (V _G1) before to provide an output timing ahead of the drive signal (V _G1) of the synchronization signal (Syn), and the synchronization The signal (Syn) is transmitted to the secondary side through an induction coil group 61, a synchronization control unit 6 obtains the synchronization signal from the induction coil group 61, and drives the synchronous rectifier switch 5 to be turned off by the synchronization signal; The side coil 12 is adjacent to a self-excited coil 2, when the pulse width is adjusted After the power switch 4 is turned off, the self-excited coil 2 is induced by a polarity change of the primary side coil 11 to induce a self-excitation signal to drive the synchronous rectification switch 5 to be turned on; when the synchronous rectification switch 5 is turned on, a conduction period is performed. The limiting unit 7 will intercept a current or voltage signal from the synchronous rectification switch 5, and thereby cause the on-period limiting unit 7 to initiate a period limit timing, wherein the pulse width modulation unit 3 generates the synchronization signal again. The synchronous rectification switch 5 is also reset to the initial state after the synchronous rectification switch 5 is turned off, and if the abnormal state or transient change occurs, the pulse width modulation unit 3 stops sending the driving signal. When the synchronous rectification switch 5 is continuously turned on until the end of the period limit timing, the on-period limiting unit 7 generates a forced-off signal to forcibly cut off the synchronous rectification switch 5 to maintain the minimum operating frequency of the flyback circuit operation; The synchronous rectification switch 5 is further connected to a synchronous rectification switch drive unit 51. The synchronous rectification switch drive unit 51 is subjected to a self-excitation signal of the self-excited coil 2. After the triggering, a sufficient voltage is provided to ensure that the synchronous rectification switch 5 is turned on. Therefore, the synchronous rectification switch driving unit 51 determines the timing of turning on the synchronous rectification switch 5 according to the synchronization signal, the forced-off signal, and the self-excitation signal; In addition to the self-excited function of the self-excited coil 2, the synchronous control unit 6 and the induction coil group 61 obtain a synchronization signal before the primary side coil is excited by the above-mentioned circuit structure. (Syn) is turned off by the synchronous rectification switch 5, and further, in order to avoid the primary side stop operation, the self-excited period of the secondary side is out of control, the on-period limiting unit 7 provides a period limit timing when the synchronous rectification switch 5 is turned on. After the period limit time is limited, the on-period limiting unit 7 forcibly turns off the synchronous rectification switch 5 to maintain the lowest operating frequency, thereby achieving the effect of avoiding the self-excitation period out of control.

Referring to FIG. 2 and FIG. 3-1 to FIG. 3-5, the schematic diagram is a circuit diagram of an embodiment of the present invention and a waveform diagram of each node of FIG. 2. In this embodiment, the synchronous rectification switch driving unit 51 includes a latching circuit of a high and low level state (mainly composed of semiconductor switches Q3, Q4) to maintain the operating state of the synchronous rectification switch 5, so that the latch circuit is triggered by the self-excited signal of the self-excited coil 2 The stable voltage ensures the conduction of the synchronous rectification switch 5; however, before the pulse width modulation unit 3 generates the drive signal (V _G1 ) to turn on the power switch 4, the pulse width modulation unit 3 first generates the synchronization signal ( Syn), triggering the semiconductor switch Q6 in the synchronous control unit 6 through the induction coil group 61, thereby pulling the gate voltage of the latch circuit in the synchronous rectification switch driving unit 51, so that the latch circuit output is in a low level state, Further, the synchronous rectification switch 5 is turned off; and when the synchronous rectification switch 5 is turned on, the conduction period limiting unit 7 draws a current or voltage signal from the synchronous rectification switch 5, and the conduction period limiting unit 7 includes a charging and discharging a loop and a reference voltage source Vcc, the charge and discharge loop is connected to the reference voltage source Vcc, and a cutoff voltage level is set, the cutoff voltage can be determined by the transition voltage of the semiconductor switch Q5, and the charge is turned on when the synchronous rectifier switch 5 is turned on The discharge circuit is charged by the reference voltage source Vcc, and the voltage charged by the charge and discharge circuit reaches the cutoff voltage level to determine the timing of generating the forced cutoff signal, in other words, when the synchronous rectifier switch 5 is continuously turned on, When the voltage of the charge and discharge circuit reaches the cutoff voltage level, the working state of the semiconductor switch Q5 will change, and the gate voltage of the latch circuit is also pulled, thereby forcing the synchronous rectifier switch 5 to be turned off, thereby ensuring the flyback circuit. The minimum operating frequency, if the synchronous rectification switch 5 is triggered by the synchronization signal, the charging and discharging circuit discharge is triggered together, so the conduction period limiting unit 7 can repeatedly repeat the initial state to restart the cycle limiting timing, and The cycle limit timing is determined by charging the charge and discharge loop to the cutoff voltage level; see Figure 3-1 to 3-5, wherein FIG. 3-1 represents the gate voltage waveform (CTL) of the synchronous rectification switch 5, and FIG. 3-2 represents the VCE voltage waveform (DR) of the semiconductor switch Q6 in the synchronous control unit 6, FIG. 3-3 It is the voltage waveform (PLL) of the secondary side coil 12 of the transformer 1, Figure 3-4 shows the waveform of the synchronization signal (Syn), and Figure 3-5 shows the capacitance of the charge and discharge circuit of the conduction period limiting unit 7. The terminal voltage waveform (V _C1 ); as can be seen from the figure, when the synchronization signal is at a high level, the synchronous rectification switch driving unit 51, the capacitance voltage of the on-period limiting unit 7, and the gate of the synchronous rectification switch 5 are caused. The voltage becomes a low level, causing the synchronous rectification switch 5 to be turned off, so that the waveforms of FIG. 3-1, FIG. 3-2, and FIG. 3-3 are lowered to a low level until the current conduction state of the primary side is changed, and then The side generates current and voltage due to self-excitation, and the charge and discharge circuit is also discharged by the synchronization signal (Syn), and the voltage waveform across the capacitor of FIG. 3-5 also falls to a low level.

Referring to FIG. 2 and FIG. 4-1 to FIG. 4-5 and the like, the diagrams of FIGS. 4-1 to 4-5 and the like represent the waveform diagrams of the nodes in the abnormal state generated by the flyback circuit in FIG. 2, wherein 4-1 represents the gate voltage waveform of the synchronous rectification switch 5, FIG. 4-2 represents the VCE voltage waveform of the semiconductor switch Q6 of the synchronous control unit 6, and FIG. 4-3 represents the two ends of the secondary side coil 12 of the transformer 1, 4-4 represents the waveform of the synchronization signal (Syn), and FIG. 4-5 shows the voltage waveform across the capacitor of the charge and discharge loop of the conduction period limiting unit 7; first, the synchronization signal (Syn) is particularly noted. After the normal output of the three pulse waves, the pulse width modulation unit 3 also stops outputting the drive signal (V _G1 ) to stop the primary side. If there is no trigger of the synchronization signal (Syn), the synchronous rectifier switch 5 will continue to conduct, especially noteworthy is the charge and discharge loop voltage of Figure 4-5, the voltage of the charge and discharge loop reaches the cutoff voltage level in Figure 4-5 (in the waveform of the simulation, the cutoff When the voltage level is about 14V), the charge and discharge circuit will generate the forced cutoff signal to force the synchronous rectifier switch 5 to cut Therefore, it can be seen that the voltage waveforms of FIG. 4-1, FIG. 4-2 and FIG. 4-3 can still maintain a low frequency normal switching, so that the flyback circuit does not lose control.

Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the present invention, and any modifications and refinements made by those skilled in the art without departing from the spirit and scope of the invention should be In the invention, the scope of the invention is therefore defined by the scope of the appended claims.

In summary, the conventional circuit of the present invention enhances the above-mentioned effects, and should fully comply with the novelty and progressive statutory innovation patent requirements, and submit an application according to law, and invites your office to approve the invention patent application, to encourage creation, to Feeling the virtues.

1‧‧‧Transformer

11‧‧‧One-side coil

12‧‧‧second side coil

2‧‧‧Self-excited coil

3‧‧‧ Pulse width modulation unit

4‧‧‧Power switch

5‧‧‧Synchronous rectifier switch

51‧‧‧Synchronous rectifier switch drive unit

6‧‧‧Synchronous control unit

61‧‧‧Induction coil set

7‧‧‧Continuation cycle limiting unit

1 is a block diagram of a circuit architecture of the present invention.

Figure 2 is a circuit diagram showing the implementation of the present invention.

Figure 3-1 is a waveform diagram (1) of the circuit diagram of the implementation.

Figure 3-2 is a waveform diagram (2) of the circuit diagram of the implementation.

Figure 3-3 is a waveform diagram (3) of the circuit diagram of the implementation.

Figure 3-4 is a waveform diagram (4) of the circuit diagram of the implementation.

Figure 3-5 is a waveform diagram (5) of the circuit diagram of the implementation.

Figure 4-1 is a waveform diagram (1) of the implementation circuit in an abnormal state.

Figure 4-2 shows the waveform (2) of the implementation circuit in an abnormal state.

Figure 4-3 shows the waveform (3) of the implementation circuit in an abnormal state.

Figure 4-4 shows the waveform (4) of the implementation circuit in an abnormal state.

Figure 4-5 shows the waveform of the implementation circuit in an abnormal state (5).

1‧‧‧Transformer

11‧‧‧One-side coil

12‧‧‧second side coil

2‧‧‧Self-excited coil

3‧‧‧ Pulse width modulation unit

4‧‧‧Power switch

5‧‧‧Synchronous rectifier switch

51‧‧‧Synchronous rectifier switch drive unit

6‧‧‧Synchronous control unit

61‧‧‧Induction coil set

7‧‧‧Continuation cycle limiting unit

Claims (6)

A flyback circuit with synchronous control, one of the secondary circuits and the secondary side respectively have one primary side coil and a secondary side coil with opposite polarity, wherein the current conduction period of the secondary side coil is controlled In a synchronous rectification switch, the flyback circuit further includes: a pulse width modulation unit that generates a driving signal to control a power switch on period of the primary side coil, and outputs the first time before generating the driving signal a synchronization signal that leads the driving signal; a synchronous control unit that acquires the synchronization signal by an induction coil group and turns off the synchronous rectifier switch with the synchronization signal; a conduction period limiting unit is After the synchronous rectification switch is turned on, a period limit timing is started, wherein after the synchronization signal turns off the synchronous rectification switch, the on period limiting unit is reset back to an initial state, and the synchronous rectification switch is continuously turned on until the end of the period limit timing The on-period limiting unit generates a forced-off signal to turn off the conduction of the synchronous rectification switch to maintain the Fly-lowest operating frequency of the circuit operation. The flyback circuit with synchronous control according to claim 1, wherein the secondary side further includes a self-excited coil coupled to the primary side coil, and a self-excited is generated by a polarity change of the primary side coil. And driving the synchronous rectification switch by the self-excited signal. The flyback circuit with synchronous control as described in claim 1 or 2, wherein the synchronous rectification switch is further connected to a synchronous rectification switch driving unit, and the synchronous rectification switch driving unit is forced according to the synchronization signal The cutoff signal and the self-excited signal determine the timing at which the synchronous rectification switch is turned on. The flyback circuit with synchronous control according to claim 3, wherein the synchronous rectification switch driving unit comprises a latch circuit having a high and low level state to control an operating state of the synchronous rectification switch. The flyback circuit with synchronization control according to claim 1, wherein the conduction period limiting unit comprises a charging and discharging circuit and a reference voltage source, the charging and discharging circuit is connected to the reference voltage source, and a cutoff is set. The voltage level determines whether the voltage of the charge and discharge circuit reaches the cutoff voltage level to determine the timing of generating the forced cutoff signal. The flyback circuit with synchronous control according to claim 5, wherein the cycle limit timing is determined by charging the charge and discharge circuit to the cutoff voltage level.