JPS5917617B2 - power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A switching type stabilized power supply circuit is configured as shown in FIG. 1, for example.

That is, in FIG. 1, a commercial AC voltage is supplied from a power plug 1 through a power switch 2 and a power filter 3 to a rectifier 5 circuit 4 where it is rectified and smoothed into a DC voltage, and this DC voltage is applied to the primary coil of a transformer 5. It is supplied to the series circuit of Li and the switching transistor 6, and at the same time, a PWM pulse from, for example, the PWM modulation circuit 16 is supplied to the transistor 6, which turns on and off. Therefore, an AC voltage is taken out from the secondary coil L2 of the transformer 5, which is supplied to the rectifier circuit T, where it is rectified and smoothed into a desired DC voltage, and this DC voltage is taken out to the output terminal 8.

5 And in order to stabilize the output voltage of this terminal 8,
Furthermore, it is structured as follows.

That is, the DC voltage at the terminal 8 is taken out by the variable resistor 11, supplied to the transistor 12, and compared with the reference voltage from the constant voltage diode 13. is supplied to the modulation circuit 16 as its modulation input. The modulation circuit 16 is also supplied with carrier wave pulses from the oscillation circuit IT. Ru. In this way, the pulse width of the PWM pulse from the modulation circuit 516 changes according to the DC voltage at the terminal 8, and the DC current at the terminal 8 is stabilized at a constant value. Also, at this time, the DC voltage from the rectifier circuit 4 is supplied through the transistor 21 to the control circuit of the transistor 6, that is, the circuits 15 to 17, as its operating voltage. In such a switching type power supply circuit, the input AC power supply side and the load side are electrically separated by the transformer 5 and the photocoupler 14.

Since the transistor 6 performs a switching operation, the efficiency is essentially high. However, in reality, the commercial AC voltage is 1
00, the DC voltage from the rectifier circuit 4 will be about 140V, whereas the operating voltage of the circuits 15 to 17 will be 6 to 1V.
The voltage is about 5V, so transistor 2 is connected by this difference.
1 and resistor 22, the efficiency decreases by this amount.

Furthermore, the transistor 21 is required to have a high breakdown voltage, which reduces reliability and increases cost. Therefore, a power supply circuit as shown in FIG. 2 has also been considered.

That is, the AC voltage obtained in the tertiary coil L3 of the transformer 5 is supplied to the rectifier circuit 23 to be converted into a DC current, and this DC voltage is supplied to the circuits 15 to 17 as their operating voltages. Therefore, in this power supply circuit, compared to the power supply circuit shown in FIG. 1, there is no decrease in efficiency or reliability.

However, in this power supply circuit, when the switch 2 is turned on, the transistor 6 is off and the DC voltage from the rectifier circuit 23 is not obtained, so the circuits 15 to 17 do not work, and therefore the PWM pulse is not output from the modulation circuit 16. is not obtained, the transistor 6 continues to be off.

In other words, this power supply circuit does not start even if the switch is turned on. For this purpose, a start circuit 24 is generally provided so that the DC voltage from the rectifier circuit 4 is supplied to the circuits 15 to 17 as their operating voltage for only a few seconds after the switch 2 is turned on. But in this case,
The cost increases due to the start circuit 24.
The present invention attempts to solve these problems.

For this reason, in the present invention, as shown in FIG. 3, for example, a transformer 5 is used to configure an oscillation circuit 30, and when the power switch 2 is turned on, the oscillation circuit 30 is operated only at this time, and the rectifier circuit 24 is activated. obtains a DC voltage, and causes the circuits 15 to 17 to be stopped by this DC voltage, and
Thereafter, the transistor 6 performs switching to maintain a steady operating state.

That is, in the example shown in FIG. 3, the transformer 5 is provided with an oscillation coil L4, an oscillation transistor 31, and capacitors 32, 37 and resistors 33, 34 are connected as shown in the figure. The oscillation circuit 30 is constructed by the following steps.

Furthermore, a series circuit of a resistor 35 and a capacitor 36 is connected as a time constant circuit to the output terminal of the rectifier circuit 24, and the connection point between the resistor 35 and the capacitor 36 is connected to the transistor 4.
Connected to the base of 1.

The transistor 41 and the transistor 42 constitute a Schmitt circuit 43 for voltage level discrimination, and the collector of the transistor 42 is connected to the base of a transistor 46 through a transistor 45, and the collector of the transistor 46 is It is connected to the connection point with 34. In such a configuration, when the switch 2 is turned on, the output voltage is not yet obtained from the rectifier circuit 24, so the transistor 45 is turned off.
Transistor 46 is also off. Therefore, when the switch 2 is turned on, the output voltage of the rectifier circuit 4 is supplied to the base of the transistor 6 through the coil L4 → resistor 33 → resistor 34, and the transistor 6 is class-A biased. Oscillation begins because the circuit 34 acts as a positive feedback path from the coil L4 to the base of the transistor 6. Note that the oscillation frequency in this case is a frequency close to the switching frequency of the transistor 6, for example, 2
It is considered to be 0KHz or higher. And when this oscillation occurs,
As a result, an output voltage can be obtained from the rectifier circuit 24, and this voltage charges the capacitor 36 through the resistor 35, but during this charging period, the transistor 41 is off, so the transistor 42 is on. , so transistor 45 is off and transistor 46 is also off, so transistor 6 continues to oscillate.

At this time, the output voltage of the rectifier circuit 24 is also supplied to the circuits 15 to 17 as their operating voltages.
When the charging voltage of the capacitor 36 reaches a certain value,
That is, when a predetermined time elapses after the switch 2 is turned on, the transistor 41 is turned on and the transistor 42 is turned on.
is turned off, transistor 45 is turned on and transistor 46 is also turned on.

When the transistor 46 is turned on, the resistor 33,
The bias current and oscillation feedback signal that had been supplied to the base of the transistor 6 through 34 are cut off, and
At this time, since the circuits 15 to 17 have already been supplied with the operating voltage from the rectifier circuit 24, the P from the modulation circuit 16 is
The transistor 6 begins to switch due to the WM pulse, and thereafter enters a steady state of operation. In this way, in the present invention, when the switch 2 is turned on, the oscillation circuit 30 oscillates and enters the steady operation state, so there is no reduction in efficiency, the structure is simple, and there is no increase in cost. Furthermore, the time constants of the resistor 35 and capacitor 36 (including the time constant of the rectifier circuit 24) keep the oscillation circuit 30 in an oscillating state for a certain period of time after the switch 2 is turned on. The operating voltage at the time of starting can be reliably supplied to the device, and the starting operation can therefore be performed reliably. Further, during steady operation, the transistor 46 is turned on and the transistor 31 is not oscillated by the coil L4, and only the transistor 6 is turned on and off by the PWM pulse from the modulation circuit 16, so that the PWM
The stabilizing operation of the output voltage of the terminal 8 by changing the pulse width of the pulse becomes effective and reliable. In the example above,
Although the oscillation circuit 30 constituted by the transistor 31 at the start is of an anti-coupling type, it can also be of a blocking type, for example.

FIG. 4 shows an example of this. When switch 2 is turned on, transistor 31 is triggered through capacitor 38, self-oscillation begins at a frequency determined by the time constant of capacitor 32 and resistor 39, and after a predetermined period, transistor 31 is triggered through capacitor 38. 46 is turned on, the transistor 3 is transferred from the coil L4.
Since the feedback of 1 to the base is no longer performed, the modulation circuit 1
Switching is performed with PWM pulses from 6 onwards.

[Brief explanation of drawings]

1 and 2 are connection diagrams for explaining this invention,
3 and 4 are connection diagrams of an example of the present invention. 16 is a PWM modulation circuit, and 1T is an oscillation circuit.

Claims (1)

[Claims] 1. A first rectifier path for rectifying and smoothing input AC voltage to extract a first DC voltage, a transformer having at least a primary coil and a secondary coil, and the primary coil at the output end of the first rectifier circuit. a switching element connected in series with the secondary coil; a second rectifier circuit connected to the secondary coil to rectify and smooth the output pressure of the secondary coil into a second DC voltage; a first detection circuit for detecting; a modulation circuit provided in the transformer; a third rectifier circuit that rectifies and smoothes the output pressure of the tertiary coil and supplies an operating voltage to at least the modulation circuit; an oscillation element; and an oscillation element provided in the transformer. a quaternary coil which together constitute an oscillation circuit, a second detection circuit which detects the rectified output of the third rectifier circuit, and another which controls the oscillation of the oscillation element by the detection output of the second detection circuit. a switching element, when the input AC voltage is supplied, the oscillation element is oscillated to supply an operating voltage from the third rectifier circuit to at least the modulation circuit, and the input AC voltage is supplied. When an output is obtained from the third rectifier circuit after the detection is performed, the detection output of the second detection circuit controls the another switching element to stop the oscillation of the oscillation element, and the output from the modulation circuit is The switching element is switched by the pulse of , the operating voltage of the modulation circuit is extracted and supplied from the third rectifier circuit, and the stabilized output voltage is obtained from the second rectifier circuit. power supply circuit.