JPH01311866A - Switching power circuit - Google Patents

Abstract

PURPOSE:To reduce the cost by operating a mode control circuit with a microcomputer in a standby state and by shortening the ON-period with a threshold value switching circuit changed over. CONSTITUTION:A switching power source is composed of a commercial power source 1, a bridge rectification diode 2, a smoothing capacitor 3, a transformer 4, a rectification diode 5 and a smoothing capacitor 6 and feeds the power to a load 7. It is also equipped with a microcomputer 9 for remote control and its power circuit 8, a transistor(Tr)10 for switching the output and its base current control circuit 11, an oscillator 12, an error amplifier 13 where a threshold switching circuit is built in and a mode control circuit 14. Further, a rectification diode 15 for a controlling coil 4b of the transformer 4 and a smoothing capacitor 16 are provided. Thus, by the use of the control voltage of the microcomputer 9 the mode control circuit 14 switches its mode, the threshold value switching circuit of the error amplifier 13 is changed over and the ON-time of the Tr 10 is varied, so that the output voltage is caused to be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a switching power supply circuit for remote control used in television receivers and the like.

[Conventional technology]

FIG. 5 is a block diagram showing a switching power supply circuit for a conventional television receiver, etc. In the figure, 1 is a commercial power supply, 2 is a bridge rectifier diode, and 3 is a smoothing circuit for smoothing the waveform rectified by the bridge rectifier diode 2. Capacitor 19 is a switching power supply whose output is connected to load 7
It is connected to the.

17 is a standby power supply for remote control, the output of which is connected to a power supply circuit 18. Reference numeral 9 denotes a remote control microcomputer (hereinafter referred to as microcomputer), the output of which is connected to a switching power supply 19.

Next, the operation will be explained. The alternating current of the commercial power supply 1 is rectified by the bridge rectifier diode 2.

The rectified waveform is converted into a DC voltage by the smoothing capacitor 3 and applied to the switching voltage 'a19.

The switching power supply 19 functions as a DC-DC converter so that an appropriate DC voltage is applied to the load 7.

On the other hand, the standby power supply SZ works regardless of whether the switching power supply 19 is inactive or in operation, and there are two cases in which the standby power supply SZ is composed of a switching power supply and a series control power supply tapped down by a low frequency transformer. There is.

The output of this standby power supply 17 is applied to a power supply circuit 18 to provide a low ripple voltage necessary for the microcomputer 9. The IT power supply path 18 is usually composed of a three-terminal IC.

The microcomputer 9 is equipped with an infrared light receiving section, allowing remote control. The output of the microcomputer 9 is switching ti! ! 19 is input. Switching i! i
l[19 is activated and deactivated by the output of this microcomputer 9. When inactive, no voltage is applied to the load 7.

Although not shown in the figure, a method of controlling the input voltage of the switching voltage f1.19 using a relay is also commonly used. The microcomputer 9 generally has functions for controlling the channel selection operation, volume, etc. in addition to turning the power ON10FF.

[Problem to be solved by the invention]

Since the conventional switching power supply circuit is configured as described above, the standby power supply 17 is configured independently of the switching power supply 19, which is the main T4 source circuit, and there is a problem in that the cost is also high.

The object of the present invention is to obtain a switching its circuit in order to solve the above-mentioned problems.

[Means to solve the problem]

A switching power supply circuit according to the present invention includes a mode control circuit for switching the voltage supplied to a load, an oscillation circuit, a transistor that performs a switching operation using the output of the oscillation circuit, and a switching period of ON/OFF of the transistor. A transformer that generates a voltage according to the ON cycle and supplies it to the load, and a transistor that turns on and off.
The built-in threshold switching circuit is switched by the base current control circuit that controls the period and the voltage generated by the transformer and the mode control circuit.
An error amplifier is provided to change the N period or 0NJi1 period.

[Function] The transistor according to the present invention controls the current at the base of the transistor with a base current control circuit based on the output signal of the oscillator, switches the transistor, and generates a predetermined voltage in the transformer, and also controls output from a microcomputer or the like. The mode control circuit switches the mode depending on the voltage, switches the threshold value switching circuit of the error amplifier, controls the base current control circuit with the output of the error amplifier, changes the ON period or ON period of the transistor, and changes the output voltage of the transformer. change.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a commercial power supply, 2 is a bridge rectifier diode, and 3 is a commercial power supply. , a smoothing capacitor for smoothing the waveform of the voltage of the source 1 rectified by the bridge rectifier diode 2, 4 is a transformer, 4a is its primary coil, 4b is a control coil, and 4C is a secondary coil.

5 is a diode that rectifies the switching frequency pulse, 6 is a smoothing capacitor, 7 is a load, 8 is an ftl5 circuit,
9 is a microcomputer for remote control.

Reference numeral 10 denotes a switching output transistor that generates a pulse in the primary coil 4a of the transformer 4, and its emitter is grounded and its collector is connected to one end of the primary coil 4a.

11 is a base current control circuit for the transistor 10; 12 is a variable frequency oscillator to which the smoothed voltage of the smoothing capacitor 3 is applied, and the oscillation output is sent to the base current control circuit 1;
I am trying to supply it to 1.

Reference numeral 13 denotes an error amplifier, which also has a built-in threshold switching circuit. 14 is a mode control circuit for switching the output voltage of the switching power supply. 15 is a diode for rectifying the output of the control coil 4b of the lance 4, and 16 is its smoothing capacitor.

The voltage smoothed by the smoothing capacitor 16 is applied to the error amplifier 13, and the error amplifier 13 switches the magnitude of the voltage and outputs it to the base current control circuit 11 and the oscillator 12.

Next, the operation will be explained. The AC voltage of the commercial power source 1 is rectified by the bridge rectifier diode 2. The rectified waveform is turned into a DC voltage by the smoothing capacitor 3, and is applied to the oscillator 12 and the primary coil 4a of the transformer 4.

The oscillator 12 starts oscillating as soon as the voltage is applied, and its output is supplied to the base current control circuit 11. The base current control circuit 11 controls the ON period or ON period of the transistor 10 according to the output of the error amplifier 13.

The transistor 10 short-circuits one of the primary coils 4a of the transformer 4 to ground during the ON period to generate pulses at the frequency of the oscillator 12. The pulse generated in the primary coil 4a is transmitted to the secondary coil 4c by M coupling, and becomes a DC voltage again at the rectifier diode 5 and the smoothing capacitor 6. The DC voltage is applied to the load 7 and the power supply circuit 8. The power supply circuit 8 has the function of converting the voltage into a voltage necessary for the microcomputer 9 and supplying the voltage.

On the other hand, the pulse generated in the primary coil 4a of the transformer 4 is also transmitted to the control coil 4b, and converted into a DC voltage by the rectifier diode 15 and smoothing capacitor 16.

The error amplifier 13 detects the magnitude of this DC voltage and inputs the information to the base current control circuit 11. The base current control circuit 11 shortens the ON period or ON period when the error amplifier input DC voltage is large, and reverses the In this case, by increasing the length, the DC voltage supplied to the load 7 is kept constant.

At the same time, the error amplifier 13 is connected to the oscillator 12, and when the input DC voltage of the input amplifier is large, the oscillation frequency of the oscillator 12 is lowered, and vice versa, the oscillation frequency of the oscillator 12 is increased, thereby reducing the DC voltage supplied to the load 7. is kept constant.

Here, when a command to enter standby mode is given to the microcomputer 9 using an infrared remote control or the like, the microcomputer 9 transfers the power control output to the mode control circuit 14.
Communicate to.

The mode control circuit 14 is connected to a threshold switching circuit built into the error amplifier 13, and by switching this threshold switching circuit, the ON period or ON period of the transistor IO can be set in the base current control circuit 11. In order to shorten the time considerably, the mode is such that the voltage supplied to the load 7 is about half or less.

When the load 7 is a TV set, the horizontal oscillation circuit stops when the supplied voltage falls below 50 to 70 V, and the load is almost always in a no-load state.

- In standby mode for boat fishing, it is necessary to suppress the power consumption of the equipment to the minimum necessary level, and this invention satisfies this condition for the reasons mentioned above.

The embodiment shown in FIG. 1 has been described above. Next, the embodiment shown in FIG. 2 will be described. 2 differs from FIG. 1 in that the output of the mode control circuit 14 is supplied to the oscillator 12 to switch the oscillation frequency. The oscillator 12 of the embodiment shown in FIG. 2 is of a fixed type and is characterized in that it can be switched between two frequencies.

The reason for this is that if the oscillation frequency is fixed, only the power supply circuit 8 and the microcomputer 9 will be loaded in standby mode, and the ON period of the transistor 10 will have to be considerably shortened. This is because collector loss increases and it becomes difficult to control the DC voltage supplied to the power supply circuit 8 at a constant level. The other components in FIG. 2 are omitted because they operate exactly the same as in FIG. 1.

Next, the embodiments shown in FIGS. 3 and 4 will be described.

Regarding the differences between FIGS. 3 and 4 from FIGS. 1 and 2, the output of the switching power supply is connected to the load 7 through the load switching circuit 20, and the output of the microcomputer 9 is connected to the mode @ type circuit. 14, and the load switching circuit 2
It is at the point where it is also connected to 0.

Regarding the differences between Figures 3 and 4, please refer to Figure 1.
Since the differences from FIG. 2 and FIG. 2 are exactly the same, the explanation will be omitted.

Next, the operation will be explained. In Figures 3 and 4,
The load switching circuit 20 is stuck in some devices, such as television receivers, which become close to no load when the supplied voltage is below a certain level (although it is not necessary, lower the supply voltage with other equipment so that C does not become no load). It is valid if

When a command is given to the microcomputer 9 to set it to standby mode, the power control output is also input to the load switching circuit 20,
The load switching circuit 20 disconnects the load 7 according to its input. This makes it possible to prevent the load 7 from operating and to reduce power consumption.

1 to 4, non-wA edge type switching is explained for the source circuit, but the transformer 4 is of an insulated type, and the output of the microcomputer 9 is passed through a photocoupler to the mode control circuit 14. If connected to the insulating type, it can also be used, and the same effects as in Figs. 1 to 4 can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the microcomputer operates the mode control circuit in the standby state, switches the threshold switching circuit with a built-in error amplifier, and controls the ON period or ON period of the transistor to the base current control circuit. Since it is configured to be short and reduce the voltage supplied to the load to the minimum required level, an independent standby power supply circuit is not required, which has the effect of realizing a significant cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a switching power supply circuit according to an embodiment of the present invention, FIGS. 2 to 4 are block diagrams of switching 1ts circuits according to other embodiments of the invention, and FIG. 5 is a block diagram of a switching power supply circuit according to another embodiment of the present invention. 8 which is a block diagram of the circuit 4...transformer, 7...load, 8...power supply circuit,
9...Microcomputer, 10...Transistor, 11...
- Base current control circuit, 12... oscillator, 13...
Error amplifier, 14...mode control circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent: Masuo Oiwa 1st figure 7° poverty direction 11, 8th; Kubowo Tei J Circular Figure 5

Claims (1)

[Claims] An oscillation circuit, a base current control circuit that controls switching of the transistor based on the output of the oscillation circuit, a transformer whose generated voltage changes according to the ON period or ON period of the transistor and supplies voltage to the load, and a microcomputer. When a predetermined voltage is generated in the transformer, a built-in threshold switching circuit switches the mode according to the output of the transformer, and the built-in threshold switching circuit switches the mode to the base current to turn on the transistor.
A switching power supply circuit equipped with an error amplifier that changes the period or ON period.