JP2008086174A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ringing choke type switching power supply, which can correspond up to a large capacity power supply, to which a conventional RCC power supply is hard to correspond, can cope with extensive capacity ranging from a small capacity to a large capacity and attains high efficiency. <P>SOLUTION: The switching power supply, with its primary and secondary sides isolated with a transformer T, is equipped with a main switch Q1 on the primary side for turning on/off the input voltage, and with a fly-back output circuit 1 on the secondary side, wherein a forward output circuit 2 is connected in parallel with the fly-back output circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply that includes a main switch that insulates primary and secondary by a transformer, includes a main switch that turns on and off an input voltage on a primary side, and includes a flyback output circuit on a secondary side.

A general ringing choke converter (hereinafter referred to as “RCC”) is self-excited variable frequency control, in other words, the voltage of the control winding of the transformer is inverted when the current of the rectifying element on the secondary side becomes zero. It is detected that the main switch is turned on (see Patent Document 1).
JP 2000-287442 A

  On the other hand, as shown in FIG. 3, the conventional forward converter is often operated with a trapezoidal wave current in order to reduce the effective current value of the main switch and the secondary side rectifying element. Therefore, the current of the rectifier element D1 on the secondary side does not become zero. Therefore, as shown in the circuit diagram of FIG. 3, a control circuit 11 is provided between the output section on the secondary side and the control terminal of the main switch Q1, and the control circuit 11 is controlled by an oscillator or the like to forcibly turn on. -PWM control to turn off is performed.

  However, since the forward type converter performs PWM control, as shown in FIG. 4, the noise is large and a magnetic reset circuit and a surge absorbing snubber circuit for the secondary side rectifier element D1 are required, which increases the circuit scale. There is a problem of growing. On the other hand, although the RCC is suitable for a small power source, if the power is increased as in the case of the forward converter, the surge voltage of the main switch increases and the efficiency decreases due to an increase in switching loss.

  The present invention has been made in view of the above problems, and provides a ringing choke type switching power supply that compensates for the disadvantages of RCC and can cope with a large capacity.

  In order to solve the above problems, a switching power supply according to the present invention includes a main switch that insulates primary and secondary by a transformer, and that turns on and off an input voltage on a primary side, and a flyback output circuit on a secondary side. A forward power circuit is connected in parallel with the flyback output circuit.

  The transformer includes a control winding, and a control circuit between a secondary-side output unit and the control terminal of the main switch. The control circuit detects an output voltage, and an ON width is determined according to the output voltage. And the main switch is controlled by detecting that the rectifying element current provided in the flyback output circuit becomes zero by the control winding.

  According to the present invention, by connecting the flyback output circuit and the forward output circuit in parallel, it is possible to cope with a large-capacity power supply that is difficult to cope with with a conventional RCC power supply, and supports a wide range of capacity from a small capacity to a large capacity. It is possible to achieve high efficiency.

  In addition, because the forward output current operates with a triangular wave with variable frequency control, there is no loss of the output diode or partial excitation of the inductor, eliminating the need for a magnetic reset circuit and surge absorbing snubber circuit required for the forward converter. At the same time, the forward output circuit compensates for the disadvantages of the RCC, whereby the transformer can be miniaturized, the circuit configuration is simplified, and the miniaturization is possible.

  Embodiments according to the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a circuit applied to a switching power supply according to the present invention. In the switching power supply according to the present embodiment, the primary and secondary are insulated by a transformer T, and the primary winding Np of the transformer T is connected to a main switch Q1 that turns on and off the input voltage. In the present invention, the primary side circuit is not limited to this embodiment.

  A flyback output circuit 1 is provided on the secondary side. Specifically, the anode of the rectifier diode D1 is connected to one end of the secondary winding Ns1 of the transformer T, and the smoothing capacitor C3 is connected to the cathode of the rectifier diode D1.

  In this embodiment, the forward output circuit 2 is connected in parallel with the flyback output circuit 1. Specifically, the second secondary winding Ns2 is connected in series with the secondary winding Ns1, and the other end of the secondary winding Ns2 is connected to the anode of the rectifier diode D2. The cathode of the freewheel diode D3 and the inductor L1 are connected to the cathode of D2. The other end of the inductor L1 is connected to the cathode of the rectifier diode D1 constituting the flyback output circuit 1, and the anode of the freewheel diode D3 is connected to the other end of the secondary winding Ns1.

  In the present embodiment, the control circuit 10 is connected to an output voltage detection circuit 12 that detects an output voltage, and an output voltage detection signal output from the output voltage detection circuit 12 It is configured to output to the control circuit 10 via the photocoupler PC.

  The transformer T includes a control winding Nc, and this control winding Nc is connected to the control circuit 10. The control circuit 10 includes an ON width control circuit 21 that controls the ON width in accordance with the output voltage, and the input of the ON width control circuit 21 is connected to the photocoupler PC. On the other hand, the control winding Nc is a winding for detecting that the current of the rectifier diode D1 provided in the flyback output circuit 1 becomes zero, and this winding Nc is a comparator 22 for comparing with the reference voltage. The comparison signal is output to the trigger circuit 23, and the trigger signal generated by the trigger circuit 23 is output.

  The control circuit 10 includes a flip-flop circuit 24. A trigger circuit 23 is connected to a set terminal of the flip-flop circuit 24, and an on-width control circuit 21 is connected to a reset terminal. The output terminal of the flip-flop circuit 24 is connected to the gate terminal of the main switch Q1 through the driver 25. As described above, the ON width is controlled according to the output voltage, and the main switch Q1 is controlled by detecting that the current of the rectifier diode D1 provided in the flyback output circuit 1 becomes zero. .

  The switching power supply according to the present invention operates as follows. FIG. 2 shows an operation waveform diagram of the switching power supply according to the present invention. First, since the switching power supply shown in the present embodiment includes the flyback output circuit 1, electromagnetic energy is accumulated in the primary winding of the transformer T when the main switch Q1 is turned on. Conversely, when the main switch Q1 is turned off, the electromagnetic energy is released to the secondary flyback output circuit 1, and power is supplied to the load.

  Further, the present invention is characterized in that the forward output circuit 2 is connected in parallel with the flyback output circuit 1. Therefore, when the main switch Q1 is turned on, a current gradually flows through the forward output circuit 2, and power is supplied to the load. Conversely, when the main switch Q1 is turned off, the supply from the primary side is lost, the electromagnetic energy accumulated in the inductor L1 is released from the forward output circuit 2, and power is supplied to the load. As a result, the output current operates with a triangular wave.

  That is, in the present invention, since the forward output circuit 2 is connected in parallel with the flyback output circuit 1, when the main switch Q1 is turned on, electromagnetic energy is accumulated in the primary winding Np of the transformer T and forward output Electric power is supplied from the circuit 2 to the load. On the other hand, when the main switch Q1 is turned off, the electromagnetic energy accumulated in the primary winding Np of the transformer T is released to the flyback output circuit 1 on the secondary side, power is supplied to the load, and the forward output circuit 2 The electromagnetic energy accumulated in the inductor L1 is released from the forward output circuit 2, and power is supplied to the load.

  Next, on / off control of the main switch Q1 in the present embodiment will be described. When the main switch Q1 is turned on, a voltage is also generated in the second secondary winding Ns2 in proportion to the voltage generated in the primary winding Np. Thereby, the current flowing through the forward output circuit 2 gradually increases. On the other hand, when the main switch Q1 is turned off, a current flows through the flyback output circuit 1. The primary winding Np and the auxiliary winding Nc generate a positive voltage also in the auxiliary winding Nc in proportion to the winding ratio. The voltage of the auxiliary winding Nc becomes a zero current signal for detecting that the current of the output circuit 1 has become zero. When the current of the flyback output circuit 1 becomes zero, the voltage of the auxiliary winding Nc is inverted. When the zero current signal becomes low level, the voltage of the zero current signal becomes lower than the reference voltage, and the comparator 22 becomes low level. Output a signal. This low level signal is converted into a trigger signal by the trigger circuit 23, this trigger signal is output to the set terminal of the flip-flop circuit 24, an ON signal is output to the main switch Q1 via the driver 25, and the main switch Q1 is turned ON. To do.

  When the main switch Q1 is turned off, the electromagnetic energy accumulated in the primary winding Np of the transformer T is released to the secondary flyback output circuit 1, and power is supplied to the load. On the other hand, the electromagnetic energy accumulated in the inductor L1 of the forward output circuit 2 is released from the forward output circuit 2, and power is supplied to the load. In this embodiment, the output voltage is detected by the output voltage detection circuit 12, and an output voltage detection signal oscillated from the output voltage detection circuit 12 is output to the control circuit 10 via the photocoupler PC. The control circuit 10 includes an ON width control circuit 21 and controls the ON width according to the output voltage. The controlled on / off signal is output to the reset terminal of the flip-flop circuit 24, and the on signal is output to the main switch Q1 via the driver 25, so that the main switch Q1 is turned on. The main switch Q1 is on / off controlled so as to repeat these operations.

  As described above, since the flyback output and the forward output are performed, the features of the flyback converter and the forward converter can be effectively utilized. When the capacity is small, the ratio of the output from the flyback output circuit 1 is large, and when the capacity is large, the ratio of the output from the forward output circuit 2 is large. Therefore, it is possible to deal with a large capacity power supply that is difficult to cope with with a conventional RCC power supply, and it is possible to deal with a wide capacity from a small capacity to a large capacity.

  In addition, since the forward output current operates with a triangular wave in the variable frequency control, the loss of the output diode and the inductor are not biased. Furthermore, since the flyback output circuit 1 and the control circuit 10 serve as a magnetic reset circuit and a surge absorbing snubber circuit necessary for the forward converter, these circuits are unnecessary. Further, when the output current is large, the forward output circuit 2 compensates for the disadvantages of the RCC that the surge voltage of the main switch increases or the transformer becomes large in order to cope with large power, so that the transformer T The size can be reduced, the circuit configuration is simplified, and the size can be reduced.

  According to the present invention, according to the present invention, by connecting the flyback output circuit and the forward output circuit in parallel, it is possible to cope with a large-capacity power supply that is difficult to cope with with a conventional RCC power supply. It is possible to deal with a wide range of capacities, and it is possible to achieve high efficiency and industrial use.

  In addition, because the forward output current operates with a triangular wave with variable frequency control, there is no loss of the output diode or partial excitation of the inductor, eliminating the need for a magnetic reset circuit and surge absorbing snubber circuit required for the forward converter. At the same time, the forward output circuit compensates for the disadvantages of the RCC, whereby the transformer can be miniaturized, the circuit configuration is simplified and the miniaturization is possible, and the present invention can be used industrially.

It is the circuit diagram which showed one Example of the switching power supply which concerns on this invention. It is an operation | movement waveform diagram in the circuit shown in FIG. It is the circuit diagram which showed the example of the conventional switching power supply. FIG. 4 is an operation waveform diagram in the conventional example shown in FIG. 3.

Explanation of symbols

T transformer Np transformer T primary winding Ns transformer T secondary winding Nc transformer T control winding Q1 main switch D1, D2 rectifier diode D3 freewheel diode C3 smoothing capacitor L1 inductor PC photocoupler 1 flyback output circuit 2 Forward output circuit 10, 11 Control circuit 12 Output voltage detection circuit 21 On width control circuit 22 Comparator 23 Trigger circuit 24 Flip-flop circuit 25 Driver

Claims (2)

It is a switching power supply with a primary switch and a secondary switch with a main switch that turns the input voltage on and off on the primary side, and a flyback output circuit on the secondary side.
A switching power supply comprising a forward output circuit connected in parallel with the flyback output circuit. The transformer includes a control winding, and a control circuit between a secondary-side output unit and the control terminal of the main switch. The control circuit detects an output voltage, and an ON width is determined according to the output voltage. And controlling the main switch by detecting that the rectifying element current provided in the flyback output circuit becomes zero by the control winding. The switching power supply according to 1.

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