JPH0777510B2 - Switching Regulator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, and more particularly to one using a drive transformer for insulating a control signal of a main switching element.

[Outline of Invention]

According to the present invention, in the switching regulator which supplies the drive pulse to the main switching element through the isolation transformer, the oscillation circuit is provided on the primary side of the isolation transformer, and the output signal of the oscillation circuit outputs the drive pulse through the isolation transformer. The power supply terminal of the control circuit for generating is added by rectification, and the output signal of the oscillation circuit is transmitted to the secondary side of the isolation transformer only when the power is turned on, and the number of partial points is reduced and stable startup is performed.

[Conventional technology]

A conventional switching regulator will be described with reference to FIG. Third
In the figure, input DC voltage is supplied to the input terminals indicated by 31a and 31b. A conversion transformer 32 having a primary side coil 33a and a secondary side coil 33b is provided, a rectifier circuit including a diode 34 and a capacitor 35 is connected to the secondary side coil 33b, and an output voltage is output to output terminals 36a and 36b. can get. 1
A collector-emitter passage of a switching transistor 37 as a main switching element is connected in series with the secondary coil 33a. A drive pulse is supplied from the drive circuit 38 to the base of the switching transistor 37.
The drive circuit 38 is supplied with the PWM-modulated pulse signal from the control unit 40 in the form of an IC via the drive transformer 39. The control unit 40 has a PWM modulation circuit that detects a variation in the output voltage and generates a pulse signal with a duty ratio that allows a constant output voltage to be obtained.

Since the output voltage is supplied to the control unit 40 as the power supply voltage, a pulse signal is not generated from the control unit 40 immediately after the power switch is turned on because no output voltage is generated. Therefore, it is necessary to activate the control unit 40 when the power is turned on. There are two methods for this activation.

The first method is to supply the output of the sub power supply 41 to the drive transformer 42, as shown by the broken line in FIG.
Diode 43 provided on the secondary side of drive transformer 42
Also, the rectified output obtained by the capacitor 44 is supplied to the control unit 40.

The second method is to connect the self-excitation driving circuit 45 to the base of the switching transistor 37. When the power is turned on, the switching transistor 37 is operated by the starting pulse from the self-excited drive circuit 45, and the secondary side rectified output of the conversion transformer 32 is supplied to the control unit 40 as the power supply voltage.

[Problems to be solved by the invention]

The first method, which requires the sub-power supply 41 and the like, has the drawback that the number of parts is large and the cost is increased. On the other hand, in the second method, there is a problem that the start-up becomes unstable due to the variation of the circuit components forming the self-excitation driving circuit 45 and the load dependence.

Therefore, an object of the present invention is to provide a switching regulator capable of stably starting a control unit and reducing the cost.

[Means for solving problems]

In the present invention, a switching regulator in which the main switching element 10 is provided on the primary side of the insulating transformer 15 and the control unit 12 for generating a drive pulse for the main switching element 10 is provided on the secondary side of the insulating transformer 15. In, an oscillation circuit 18 provided on the primary side of the isolation transformer 15, and a circuit 13 that rectifies an output signal of the oscillation circuit 18 to a power supply terminal of the control unit 12 via the isolation transformer 15 and adds the output signal.
Isolation transformer for the output signal of the oscillation circuit 18 only when the power is turned on
A circuit 19 or 23 for transmitting to the secondary side of 15 is provided.

[Action]

The isolation transformer 15 performs bidirectional transmission, and at startup, the output signal of the oscillation circuit 18 is supplied to the rectification circuit provided on the secondary side via the isolation transformer 15, and the rectified output is supplied to the power supply terminal of the control unit 12. Supplied. During normal operation, the control unit 12
The PWM-modulated pulse signal is supplied to the drive circuit 11 of the main switching element 10 via the isolation transformer 15. Therefore, the number of parts and cost can be reduced, and stable startup can be performed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 1 is an AC power source, 2 is a power switch, and 3 and 4 are diodes and capacitors that form a rectifying circuit on the input side. The output voltage of the rectifier circuit on the input side is supplied to one end of the primary coil 6a of the conversion transformer 5,
The other end of this primary side coil 6a is a switching transistor
Grounded via 10 collectors and emitters. A rectifier circuit including a diode 7 and a capacitor 8 is connected to the secondary coil 6b of the conversion transformer 5, and the output terminals 9a and 9b are connected.
The output voltage is obtained at.

Reference numeral 12 indicates an IC control unit, for example. The control unit 12 includes
A comparison circuit that compares the output voltage with the reference voltage, an error amplifier that amplifies the error signal from the comparison circuit, and a PWM modulation circuit that controls the duty ratio according to the output signal of the error amplifier are provided. The output voltage is supplied to the power supply terminal of the control unit 12 through the diode 13. Control unit 12
The PWM modulation signal formed by is supplied to the terminal c of the switch circuit 17 via the secondary coil 16b and the primary coil 16a of the drive transformer 15. The input terminal of the drive circuit 11 is connected to the terminal b of the switch circuit 17.

The output signal of the oscillation circuit 18 that generates a pulse signal is supplied to the terminal a of the switch circuit 17. The switch circuit 17 and the oscillator circuit 18 are controlled by an output signal of a mono-multi (monostable multivibrator) 19. Mono Multi 19
Is triggered when the power switch 2 is turned on, and generates a pulse signal that is at a high level for a predetermined time after the power switch 2 is turned on. While the pulse signal is at the high level, the oscillation circuit 18 performs the oscillation operation and the switching circuit
17 terminals a and c are connected. When the output pulse of the monomulti 19 is low level, the terminal b of the switch circuit 17
And c are connected. The diode 20 and the capacitor 21 are connected in series with the secondary coil 16b of the drive transformer 15, and this rectified output is given to the control unit 12 as a power supply voltage.

The drive circuit 11, the oscillating circuit 18, and the monomulti 19 are supplied with power supply voltage from the rectifying circuit on the input side. Further, as an example, the frequency of the pulse signal formed by the control unit 12 is set to 50 [kHz], and the oscillation frequency of the oscillation circuit 18 is set to 300 [kHz].

In the above configuration, when the power switch 2 is turned on, the monomulti 19 is triggered and the output signal of the monomulti 19 rises. The oscillation circuit 18 oscillates while the output signal of the mono-multi 19 is at a high level, and the switching circuit
The terminals a and c of 17 are connected, and 2 of the drive transformer 15 is connected.
The output signal of the oscillation circuit 18 is transmitted to the next side. The output signal of the oscillator circuit 18 is rectified by the diode 20 and the capacitor 21 and supplied to the control unit 12 as a power supply voltage.

When the output signal of Mono Multi 19 falls to low level,
The new generation of the oscillator circuit 18 is stopped, and the terminals b and c of the switch circuit 17 are connected. The controller 12 includes a capacitor 21
A pulse signal is generated by the voltage stored in the drive transformer 15, the pulse signal is transmitted from the secondary side to the primary side of the drive transformer 15, and is further supplied to the drive circuit 11 via the switch circuit 17. Therefore, the switching transistor
10 performs switching operation, 2 of the drive transformer 5
A rectified output is generated on the next side, the output voltage is taken out to the output terminals 9a and 9b, and is supplied to the control unit 12 as a power supply voltage.

FIG. 2 shows another embodiment of the present invention. In another embodiment, one of the drive transformers 15 is
Coils 16a and 16c are provided on the secondary side, and coils 16b and 1 are provided on the secondary side.
Provide 6d. The primary coil 16a is connected to the input side of the drive circuit 11, and the primary coil 16c is connected to the output side of the oscillator circuit 18. The secondary coil 16b has a diode 2
A rectifier circuit including 1 and a capacitor 22 is connected, and the output voltage of the rectifier circuit is supplied to the control unit 12 as a power supply voltage. The secondary coil 16d is connected to the output side of the control unit 12.

The oscillation path 18 is supplied with a control signal from an oscillation stop circuit 23, which is surrounded by a broken line. The oscillation stop circuit 23 includes a diode 24, a resistor 25 and a capacitor 26 for rectifying a pulse signal generated at one end of the primary coil 16a of the drive transformer 15, and a resistor for transmitting a rectified output to the base of the transistor 29. It is composed of 27 and 28. When a pulse signal is generated in the primary coil 16a of the drive transformer 15, the transistor 29 is turned on by the voltage obtained by rectifying the pulse signal. The oscillation circuit 18 oscillates while the transistor 29 is on, and when the transistor 29 is on,
Stop the oscillation operation.

In the configuration shown in FIG. 2 described above, when the power switch 2 is turned on, the oscillating circuit 18 starts oscillating operation, and the oscillation output signal is composed of the diode 21 and the capacitor 22 via the coils 16c and 16b of the drive transformer 15. It is supplied to the rectifier circuit. Therefore, the power supply voltage is supplied to the control unit 12,
From 12, a PWM modulated pulse signal is generated. This pulse signal is the coil 16d and the coil 16a of the drive transformer 15.
Is supplied to the drive circuit 11 via the switch transistor 10, the switching transistor 10 starts the switching operation, and becomes the normal operation. After the pulse signal is generated in the coil 16a, the resistance 25,2
The transistor 29 is turned on for a predetermined time determined by the values of 7, 28 and the capacitor 26, and the oscillation operation of the oscillation circuit 18 is stopped.

In addition, in one embodiment shown in FIG.
Instead of using 19, the oscillation stop circuit 23 shown in FIG. 2 may be used.

〔The invention's effect〕

According to the present invention, since bidirectional transmission is performed by the drive transformer, compared to the configuration using the self-excited drive circuit, the control unit can be stably started regardless of variations in circuit components and load dependence. The number of parts can be reduced and the cost can be reduced as compared with the configuration using the sub power supply.

[Brief description of drawings]

FIG. 1 is a connection diagram of an embodiment of the present invention, FIG. 2 is a connection diagram of another embodiment of the present invention, and FIG. 3 is a connection diagram used for explaining a conventional switching regulator. Description of main symbols in the drawings 2: Power switch, 9a, 9b: Output terminal, 10: Switching transistor, 11: Drive circuit, 12: Controller, 15: Drive transformer, 17: Switch circuit, 18: Oscillation circuit, 23 : Oscillation stop circuit.

Claims (1)

[Claims] 1. A switching regulator in which a main switching element is provided on the primary side of an insulation transformer and a control section for generating a drive pulse for the main switching element is provided on the secondary side of the insulation transformer. An oscillating circuit provided on the primary side of the insulating transformer, a means for rectifying an output signal of the oscillating circuit to a power supply terminal of the control unit via the insulating transformer, and a means for adding the output signal of the oscillating circuit only when power is turned on. And a means for transmitting the output signal to the secondary side of the isolation transformer.