JPS5834991B2 - DC constant voltage power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC constant voltage power supply circuit that uses transistors that open and close at a frequency that has a predetermined relationship with a reference frequency for operating equipment.

A conventional power supply circuit of this type had a configuration as shown in the block diagram shown in FIG.

In FIG. 1, which shows the application to a television receiver, when an AC voltage of 100 V is connected to the commercial frequency power input terminal 1, a DC voltage of about 140 V is obtained at the output of the first rectifying and smoothing circuit 2.

A part of this direct current is transmitted to the self-propelled multi-pipe brakes Qtrs1 and 6. L-Juice White Maru Jinno
A pulse with a constant frequency (approximately 15 KHz) is supplied from R to the pulse width control circuit 7.

The output of the pulse width control circuit 7 drives the base of the switching transistor 3, and the 140V DC is applied to the switching transistor 3.
The signal is chopped at a free-running multi-by-break 60 frequency and supplied to the primary side of the insulating pulse transformer 4.

The chopping voltage generated on the secondary side of the insulated pulse transformer 4 is converted into direct current by the second rectifying and smoothing circuit 5 and then sent to the direct current output terminal 1.
2.

A part of the DC output becomes a power source for the horizontal oscillation circuit 10, which generates a pulse with a horizontal scanning period (for example, 15.734 Kflz in the case of NTSO standard broadcasting).
The pulses are applied to the free-running multi-vib break 6 via an auxiliary insulating pulse transformer 11.

Therefore, the output of the free-running multi-by-break 6 is synchronized with the pulse of the horizontal scanning period, and therefore the opening/closing frequency of the transistor 3 is also synchronized with the horizontal frequency.

The reason why the switching frequency is synchronized with the horizontal scanning frequency is that by synchronizing it, even if there is a ripple in the switching cycle at the DC voltage terminal 12, the received image will not be disturbed.

That is, if they are not synchronized, the ripples in the opening/closing period will appear on the screen as fluctuations in the beat frequency with the horizontal frequency, and even the slightest ripple will not be tolerated, and an expensive LC filter will be required after the DC voltage output terminal 12. .

When synchronized, the ripple becomes curved on the screen,
The detection limit for bending is much softer than the detection limit for shaking, and even a ripple voltage 10 times larger can be tolerated.

A part of the voltage at the DC output terminal 12 is negatively fed back to the pulse width control circuit 7 through an error voltage amplifier 9 consisting of a comparator with a reference voltage (for example, the Zener voltage using a Zener diode) and a photocoupler 8. .

That is, when the voltage at the output terminal 12 rises above the reference value, the output of the pulse width control circuit 7 has a pulse width that shortens the conduction time of the switching transistor 3;
When the voltage drops below the reference value, the pulse width becomes such that the conduction time of the switching transistor 3 becomes longer, and the output terminal 12
We are trying to stabilize the voltage of the

In this case, a photocoupler 8 is used to transmit DC from the secondary side of the insulated pulse transformer 4 to the primary side while maintaining insulation, but this element is expensive and is used as a power source for consumer equipment where cost competition is fierce. It is difficult to use it in circuits.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-cost DC constant voltage power supply circuit that can overcome the above-mentioned drawbacks and can be used in consumer equipment.

Therefore, the present invention provides a chopper circuit that chops a DC voltage that has a predetermined relationship with the output DC voltage of a rectifying and smoothing circuit at a frequency that has a predetermined relationship with the frequency that is the reference frequency for device operation, and a chopper circuit that transmits the output of the chopper circuit to the switching transistor side. It is characterized by being equipped with an auxiliary isolation transformer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. Reference numerals 1 to 7, 9 to 12 indicate the same components as in FIG.
14 is a second rectifying and smoothing circuit to which the output of the chopper circuit 13 is applied via the auxiliary isolation transformer 11.

In this configuration, the auxiliary isolation transformer 11 can be similar to the one shown in FIG. 1, and it transmits both the DC information regarding the error voltage and the horizontal oscillation frequency.

The error voltage obtained by comparing the voltage at the output terminal 12 of the DC voltage with the reference voltage in the error voltage amplifier 9 is applied to the chopper circuit, and is chopped by the output from the horizontal oscillation circuit 10 to generate a pulse according to the above-mentioned error voltage. The voltage has a peak value.

The auxiliary isolation transformer 11 has a repetition frequency equal to the output voltage of the chopper circuit 13, that is, the horizontal scanning frequency, and transmits a pulse voltage whose peak value corresponds to the error voltage to the negative side, and a part of it is transmitted to the free-running multi-by-break 6. The other part controls the pulse width control circuit 7 in a direction in which the error voltage becomes zero.

The operation of the switching transistor 3 is the same as in FIG.

The above explanation was an example in which the input to the chopper circuit 13 is chopped at the output of the error voltage amplifier 9 and one horizontal oscillation frequency. It may be something that has been done.

In addition, the chopping frequency only needs to have a predetermined relationship with the frequency that serves as a reference for equipment operation, like the horizontal scanning frequency.
For example, it may be an integer multiple or an integer fraction of the reference frequency.

Conventionally, photocouplers have been used as power supply circuits to obtain constant DC voltage in devices such as television receivers, television imagers, video tape recorders, and video discs that have a built-in frequency generator that serves as a reference for operation. However, the present invention does not require expensive elements and is equipped with a chopper circuit that can be constructed from inexpensive parts, thereby providing performance sufficient to be used as consumer equipment at a low price. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional power supply circuit, and FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. 1... Terminal of AC input power supply, 2... First rectifying and smoothing circuit, 3... Switching transistor, 4
......Isolation transformer, 9...Error voltage amplifier, 10...Horizontal oscillation circuit, 11...
Auxiliary isolation transformer, 13... Chopper circuit.

Claims (1)

[Claims] 1 A switching transistor that switches and controls a voltage obtained by rectifying AC input, an isolation transformer, and a rectifying and smoothing circuit are connected in cascade,
In a power supply circuit that controls the opening/closing time of a switching transistor with a time corresponding to the error voltage generated in the output of the rectifying and smoothing circuit to obtain a constant DC voltage, a DC voltage having a predetermined relationship with the output DC voltage of the rectifying and smoothing circuit is controlled by the device. 1. A power supply circuit comprising: a chopper circuit that chops at a frequency that has a predetermined relationship with a reference frequency for operation; and an auxiliary isolation transformer that transmits the output of the chopper circuit to a switching transistor.