JPS6277865A - Power supply device - Google Patents

Abstract

PURPOSE:To reduce the burden of a starting circuit, and to improve efficiency by operating a power supply as a capacitor-input system backup power supply immediately after oscillation is started and working the power supply as a choke-input system backup power supply at a normal operation time. CONSTITUTION:A power supply device with a pulse width modulation control circuit 3 is constituted of a starting circuit 1, a switching-transistor 4, a transformer 5, diodes 6-7, a choke-coil 8, a voltage monitor 9 and a backup power supply BS. Both-end voltage VB of a capacitor 11 organizing the backup power supply BS is applied to a power terminal for the PWM control circuit 3. Transistors 21, 22, a Zener-diode 23 and a diode 24 are fitted to the power supply BS, the transistor 21 is turned OFF by the Zener-diode 23 when the voltage of the capacitor 11 is small, and the power supply BS is operated as a choke-input system when output voltage rises and exceeds Zener voltage.

Description

[Detailed Description of the Invention] [Summary] In a power supply device having a pulse width modulation control circuit 027 on the primary side, the characteristics of a capacitor-type backup power supply and a choke It has both the characteristics of an input-type backup power source.

[Industrial application field]

The present invention relates to a power supply device having a pulse width modulation control circuit, and particularly to a backup power supply that supplies power to the pulse width modulation control circuit.

[Conventional technology and problems]

FIG. 3 is a diagram showing a conventional example of a power supply device having a pulse width modulation control circuit. In Fig. 3, 1 is a starting circuit;
2 is a series regulator, 3 is a pulse width modulation control circuit (hereinafter referred to as PWM control circuit), and 4 is a switching circuit.
Transistor, 5 is a transformer, 6 and 7 are diodes, 8 is a choke coil, 9 is a voltage monitor, 10 is a diode, 11 is a capacitor, 12 is also a capacitor, BS is a backup power supply, N, to N3 are transformer windings Each line is shown. The starting circuit 1 is for supplying power to the series regulator 2 and the PWM control circuit 3 at the time of starting. The series regulator 2 is for keeping the power supply voltage supplied to the PWM control circuit 3 at a constant value. The PWM control circuit 3 turns on and off the switching transistor 4 according to the voltage value detected by the voltage monitor 9. A voltage is induced in the winding N of the transformer 5 by turning on and off the switching transistor 4, and a current flows through the load. The output voltage of the power supply device is detected by a voltage monitor 9. When switching transistor 4 turns on and off, a voltage is induced in winding 'faN2 of transformer 5, and capacitor 11 is charged by this voltage. The voltage Vll across the capacitor 11 is the voltage Vll of the diode 1o.
If the voltage drop is ignored, VB = VccXNz /N+. However, VCC is an input voltage. diode 1
0, the capacitor 11, and the winding N2 constitute a capacitor input type backup power supply BS. The voltage (2) across the capacitor 11 is supplied to the power supply terminal of the PWM control circuit 3 via the series regulator 2.

FIG. 4 is a diagram showing another conventional example of a power supply device having a pulse width modulation control circuit. In FIG. 4, 13 indicates a choke coil, and 14 indicates a diode. Note that the same reference numerals as in FIG. 3 indicate the same parts. When the switching transistor 4 is turned on and a voltage is induced in the winding N2, current flows through the bus consisting of the winding N2, the diode 10, the coil 13, and the capacitor 11, and when the switching transistor 4 is turned off, the diode 14 , the choke coil 13 and the capacitor 11. Ignoring the voltage drops caused by diodes 10 and 14, the voltage VB across capacitor 11 is Va = VCCX N2 / NI X D. However, D is the on-time of the switching transistor divided by the period. Winding N2, diode 10,
The diode 14, choke coil 13, and capacitor 11 constitute a choke input type backup power supply BS. In addition, in the conventional example shown in Fig. 4, PW
The M control circuit 3 has a soft start function, that is, a function of gradually increasing the output voltage.

FIG. 5 is a diagram showing an example of the starting circuit l. In FIG. 5, 15 is a transistor, 16 is a Zener diode, 17 is a diode, and 18 is a resistor. The output voltage ■ from the diode 17 is V=Vz VBt Vt. However, (2) indicates the voltage drop across the Zener diode 16, VBE indicates the voltage drop between the base and emitter of the transistor 15, and VF indicates the voltage drop across the diode 17, respectively. The output voltage of the series regulator 2 is set to be higher than the above voltage ■.

When a capacitor input method as shown in FIG. 3 is adopted, the voltage of the backup power supply changes in proportion to the input voltage Vcc, so it must be stabilized before use. Although the method shown in FIG. 3 allows the backup power source to start up quickly, it has the drawback of large loss. In addition, when a choke input method as shown in Fig. 4 is adopted, the loss is small, but the software of the PWM control circuit
The disadvantage is that the start-up is slow due to the start.

[Purpose of the invention]

The present invention is based on the above consideration, and provides a power supply device having a pulse width modulation control circuit and a backup power supply for supplying power to the pulse width modulation control circuit. Operates as an input-type backup power supply and then as a series
The purpose is to provide a backup power supply that operates as a regulator and, in steady state, as a backup power supply for the choke input method.

[Means to achieve the purpose]

Therefore, the power supply device of the present invention includes an input power source,
A transformer having one end of a primary winding connected to one side of the input power source, and one end connected to the other end of the primary winding of the transformer and the other end connected to the other side of the input power source. a switching transistor, a rectifier and smoothing circuit on the output side connected to the output side winding of the transformer, a voltage monitor that monitors the output voltage of the rectifier and smoother circuit, and a voltage monitor that monitors the output voltage according to the positive value detected by the voltage monitor. a pulse width modulation control circuit that controls the on-time width in one cycle of the switching transistor; a backup power supply that supplies power to the pulse width modulation control circuit; and a pulse width modulation control circuit that controls the pulse width modulation when the backup voltage of the backup power supply is low. In the power supply device, the backup power supply includes an auxiliary winding of a transformer whose one end is connected to the other side of the input power supply, and an anode side of which is connected to the other side of the auxiliary winding. a choke coil with one end connected to the cathode side of the first diode, one end connected to the other side of the choke coil and the other end connected to the input power source other than the input power source. a second diode whose anode side is connected to the other side of the input power supply and whose cathode side is connected to the cathode side of the first diode; and one end of the capacitor is controlled by the pulse width modulation control. It is provided between the power line connected to the power supply terminal of the circuit and one end and the other end of the choke coil, and when the voltage across the capacitor is low, it is in a short-circuited state, and when the voltage across the capacitor is high, it is in an open state. The device is characterized in that it is comprised of switching means.

[Embodiments of the invention]

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is an electrical circuit diagram of one embodiment of the present invention. In FIG. 1, 21 and 22 are transistors, 23 is a Zener diode, and 24 is a diode, respectively. Note that the same reference numerals as in FIG. 4 indicate the same parts. When the voltage of capacitor 11 is small, no current flows through Zener diode 23 and transistor 21 is turned off. For this purpose, the transistor 22 becomes conductive and the diode 10,
Current flows through the resistor, transistor 22 and diode 24, charging the capacitor 11.

When the output voltage becomes high and the voltage of capacitor 11 exceeds the Zener voltage of Zener diode 23, transistor 21 is turned on and transistor 22 is turned off. When the transistor 22 is off, the backup power supply BS
operates as a choke input type backup power supply.

FIG. 2 is a diagram illustrating the difference in start-up characteristics of the backup power supplies in FIGS. 3, 4, and 1. Figure 2 (
Figure 2 (a) shows the rise of the input voltage, Figure 2 (b) shows the rise of the backup power supply using the capacitor input method, Figure 2 (C) shows the rise of the backup power supply using the choke input method, and Figure 2 (C) shows the rise of the backup power supply using the choke input method. Figure (d)
shows the start-up of the backup power supply according to the present invention.

As shown in FIG. 2(d), in the variable-up power supply according to the present invention, the backup voltage VB rises rapidly with the start of oscillation, and then the backup voltage is maintained at the Zener voltage of the Zener diode 23, and the duty cycle of the transistor 4 increases. When the voltage across the capacitor 11 increases and the voltage across the capacitor 11 exceeds the Zener voltage of the Zener diode 23, the power supply has characteristics of a choke input type backup power supply.

〔Effect of the invention〕

As is clear from the above explanation, by employing the backup power supply of the present invention, a stabilized backup voltage can be obtained from low input voltage to high input voltage.
Fast start-up characteristics reduce the burden on the startup circuit,
During steady state, loss can be reduced and efficiency can be increased.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram of one embodiment of the present invention, and FIG. 2 is an electrical circuit diagram of one embodiment of the present invention.
Figure 4 is a diagram explaining the difference in the start-up characteristics of the backup power supply in Figure 1, Figure 3 is a diagram showing a conventional example of a power supply device with a pulse width modulation control circuit, and Figure 4 is a diagram showing a pulse width modulation control circuit. FIG. 5 is a diagram showing another conventional example of a power supply device having a control circuit, and FIG. 5 is a diagram showing an example of a starting circuit. 1... Starting circuit, 2... Series regulator,
3... Pulse width modulation control circuit, 4... Switching transistor, 5... Transformer, 6 and 7... Diode, 8... Choke coil, 9... Voltage monitor, 10... ...Diode, 11...Capacitor, 12
...Capacitor, BS...Backup power supply, N,
or N,...Transformer winding, 13...Choke...
Coil, °14...Diode, 15...Transistor, 16...Zener diode, 17...Diode, 18...Resistor, 21 and 22...Transistor, 23...Zener diode , 24...diode.

Claims (1)

[Claims] an input power source; a transformer having one end of its primary winding connected to one side of the input power source; and one end connected to the other end of the primary winding of the transformer and the other end connected to the other side of the input power source. a switching transistor connected to the output side of the transformer; a rectifier and smoothing circuit on the output side connected to the output side winding of the transformer; a voltage monitor that monitors the output voltage of the rectifier and smoothing circuit; and a voltage detected by the voltage monitor. a pulse width modulation control circuit that controls the on-time width in one cycle of the switching transistor according to a value; a backup power supply that supplies power to the pulse width modulation control circuit; In the power supply device, the backup power supply includes an auxiliary winding of a transformer whose one end is connected to the other side of the input power supply, and an anode side of which is connected to the auxiliary winding. a first diode connected to the other end; a choke coil having one end connected to the cathode side of the first diode; and one end connected to the other side of the choke coil and the other end connected to the input power source. with a capacitor connected to the other side of
A second diode whose anode side is connected to the other side of the input power source and whose cathode side is connected to the cathode side of the first diode.
a diode, a power line connecting one end of the capacitor to the power supply terminal of the pulse width modulation control circuit, and one end and the other end of the choke coil, and is short-circuited when the voltage across the capacitor is low. and switching means that becomes open when the voltage across the capacitor is high.