JPH03139171A - Voltage converting circuit for ac power supply - Google Patents

Abstract

PURPOSE:To eliminate large power loss and to convert source voltage efficiently into a low voltage by operating a voltage converting circuit in charging mode when full-wave rectified output is fed through a cut-off circuit whereas operating the voltage converting circuit in discharge mode, with electrical quantity 1/n of that in charging mode, when the full-wave rectified output is cut off. CONSTITUTION:A smoothing circuit B charges respective capacitors C1, C2 through a path of the capacitor C1 a diode D4 the capacitor C2 until a moment when the output from a full-wave rectifying circuit FR reaches a cut-off voltage Vc. When the output from the full-wave rectifying circuit FR reaches the cut-off voltage Vc to turn a transistor TR3 OFF, the capacitors C1 and C2 are discharged through diodes D5 and D3 respectively. Consequently, discharge starting voltages (for the capacitors C1, C2) are halved when compared with the maximum charging voltage (for the combination of the capacitors C1, C2).

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a voltage conversion circuit for an AC power supply, and particularly to a voltage conversion circuit for converting an AC power supply into a DC low voltage drive type such as a light emitting diode by full-wave rectification of the output of an AC power supply. The present invention relates to a voltage conversion circuit that converts an AC power source to a low DC voltage when used as a power source for driving a load.

(Prior art) When obtaining the low DC voltage required to drive the light emitting diodes built into a lighting switch by full-wave rectification of a commercial AC power supply, for example, the light emitting diodes are driven at low voltage, so It is necessary to convert AC power to low voltage.

In conventional conversion to low voltage, the output of the AC power source is first stepped down by a resistor installed in the front stage of the full-wave rectifier circuit, then full-wave rectified by the full-wave rectifier circuit, and the full-wave rectified output is There is a system that converts the voltage into DC using a smoothing circuit and a constant voltage circuit.

(Problem to be Solved by the Invention) By the way, if the output of the AC power supply is significantly dropped to the required value using a resistor as in the above method, there is a problem that the power loss in the resistor becomes extremely large. be.

Therefore, for example, it is conceivable to not provide this resistor, or even if it is provided, to step down the AC power supply a little with a resistor with a small resistance value, and then perform full-wave rectification and smooth it with a smoothing circuit. The smoothed output is large because the power supply voltage is not stepped down, or it is only stepped down slightly, so in a constant voltage circuit, the voltage is stepped down sufficiently to the low DC voltage required by the light emitting diode, and the voltage is constant. It will be necessary to make it

However, if the smoothed output is greatly reduced, the problem remains that power loss and heat generation in the transistors forming the constant voltage circuit become large.

In the present invention, the voltage of the AC power supply is converted to a low voltage at the downstream side of the full-wave rectifier circuit, thereby solving the problem of power loss caused by the resistance. A voltage conversion circuit that can efficiently convert low voltage to low voltage without causing large power loss in the transistors that make up the constant voltage circuit or causing the transistors to generate heat. is intended to provide.

(Means for Solving the Problems) In order to achieve such an object, the voltage conversion circuit of the present invention outputs a full-wave rectified AC power source, and the full-wave rectified value exceeds the cutoff voltage. A cut-off circuit cuts off the full-wave rectified output when the voltage exceeds the limit, and when the full-wave rectified output is applied through the cut-off circuit, it becomes a charging mode and charges the full-wave rectified output. , a smoothing circuit that enters a discharge mode when the full-wave rectified output is cut off by the cutoff circuit and discharges with an amount of electricity equal to l/n in the charging mode; It is characterized by being equipped with a constant voltage circuit that stabilizes the voltage at a voltage lower than the value.

(Function) The cutoff circuit rectifies the alternating current power, and
AC power that exceeds the cutoff voltage is cut off.

Then, the full-wave rectified output from this cutoff circuit is applied to a smoothing circuit and charged there when the cutoff circuit is not in cutoff mode. Furthermore, when the cutoff circuit is in the cutoff mode, the full-wave rectified output that has been charged in this smoothing circuit is discharged. Since the amount of discharged electricity in this case is l/n of the amount of charged electricity, the constant voltage circuit can make the output of the smoothing circuit a constant voltage without large power loss.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a voltage conversion circuit including a cutoff circuit for an AC power supply according to an embodiment of the present invention, FIG. 2 is a diagram showing a modification of the smoothing circuit of FIG. 1, and FIG. 2 is a voltage waveform diagram of each part used to explain the operation of the voltage conversion circuit. FIG.

The voltage conversion circuit shown in FIG. 1 includes a cutoff circuit A,
It consists of a smoothing circuit B and a constant voltage circuit C.

The cutoff circuit A includes a full-wave rectifier circuit FR that performs full-wave rectification of an AC power supply (not shown) applied to input terminals IN and IN. The full-wave rectifier circuit PR outputs a full-wave rectified output as shown in FIG. 3(a). A protective Zener diode DI is connected in parallel to the full-wave rectifier circuit FR. The full-wave rectifier circuit PR also includes voltage dividing resistors Rta and Rl.
b, Rlc, a Zener diode D2 that turns on (conducts) when the output of the full-wave rectifier circuit FR exceeds the cutoff voltage Vc, and a resistor R3 that generates a predetermined bias voltage with the on-current of this Zener diode D2. are connected in parallel to each other in series.

Transistor T as first transistor switch means
RI has its base and emitter connected in parallel to resistor R3. Transistor TR[ is turned on by being driven by a bias voltage generated in resistor R3. Transistor TR as second transistor switch means
2TR3 is Darlington-connected, and the collector and emitter of the transistor TR3 are connected in series between the output of the full-wave rectifier circuit FR and the output of the cutoff circuit A. Transistor TR2 is transistor TRI
When is off, voltage dividing resistor R1a=RIc and resistor R5
When the transistor TRI is on, the drive voltage is no longer applied and the transistor TRI is turned off. Transistor TR3 is also turned on and off in response to turning on and off of transistor TR2.

In this way, in the cutoff circuit A, the transistor TR3 is turned on and off depending on whether the output of the full-wave rectifier circuit FR is below or exceeds the cutoff voltage Vc, as shown in FIG. The output of the full-wave rectifier circuit PR shown in ) is converted to a low voltage as shown in FIG. 3(b) and output.

Note that even if only this cutoff circuit A is used, the output terminal OUT
The light emitting diode connected between OUT can be driven, but since the output of the cut-off circuit A is alternating current, the light emitting diode will blink. Therefore, in order to drive the light emitting diode with direct current, it is necessary to convert the output of the cutoff circuit A into direct current. The smoothing circuit B and the constant voltage circuit C are used to make the output of the cutoff circuit A a DC constant voltage.

Smoothing circuit B is connected in series with cutoff circuit A.
The diodes D3 to D5 are connected in parallel to the diodes D3. A capacitor C1 connected in parallel with D4, and a diode D4. ．． Capacitor C connected in parallel with D5
It is composed of 2.

This smoothing circuit B charges each capacitor C1 via the path of capacitor CI-diode D4-capacitor C2 with a charging waveform as shown in FIG. , C2 (the highest charging voltage is approximately Vc), and when the output of the full-wave rectifier circuit PR reaches the cutoff voltage VC and the transistor TR3 is turned off, the diode D5 is charged from the capacitor CI.
and from capacitor C2 to diode D3.
They are discharged with a discharge waveform as shown in FIG. 3 (ll) (discharge starting voltage is approximately 1/2 Vc).

Therefore, the smoothing circuit B has a discharge starting voltage (capacitors C1, C2,
The discharge voltage of C2 alone is 1/2 of that.

Although this embodiment shows a circuit example in which the amount of electricity during discharging is set to I/2 of that during charging,
For example, when reducing it to 1/3, it is configured with a smoothing circuit as shown in Figure 2 (a), and when reducing it to 1/4, it is configured with a smoothing circuit as shown in Figure 2 (b). It is possible to arbitrarily reduce the amount of electricity to 1/n of that during charging.

The constant voltage circuit C includes a Zener diode D6 connected between output terminals OUT and OUT, whose on voltage is set to a voltage Vd lower than 1/2Vc corresponding to the drive voltage of the light emitting diode, and a resistor R6 connected in series with each other. In this state, the transistor TR4 is connected in parallel to the smoothing circuit B, and the transistor TR4 has its collector and emitter connected between the smoothing circuit B and the output terminal OUT.

In the constant voltage circuit C, the output of the smoothing circuit B having a waveform as shown in FIG. 3(C) is converted into a constant voltage defined by the Zener diode D6 and output as shown in FIG. 3(d). It has become. Here, since the smoothing circuit B provides the constant voltage circuit C with a waveform output as shown in FIG. 3(c), even if the Zener diode D6 is turned on and the transistor TR4 is turned on, this transistor TR4 is Fever is now under control. To be more specific, the discharge voltage of Vc is directly output from the smoothing circuit B to the constant voltage circuit C, and the constant voltage circuit C calculates 1 from the discharge voltage of Vc.
/2 If the voltage is lowered all at once to a Vd lower than Vc, there is a problem in that the heat generation effect in the transistor TR4 increases. Therefore, in order to suppress the above heat generation effect, the smoothing circuit B lowers the voltage output to the constant voltage circuit C to I/2Vc at the start of discharge.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
The AC power supplied to the cut-off circuit is full-wave rectified by the cut-off circuit, and AC power exceeding the cut-off voltage is cut off here, and the full-wave rectified output from this cut-off circuit is as follows: When the cutoff circuit is not in the cutoff mode, it is applied to the smoothing circuit and charged there, and when the cutoff circuit is in the cutoff mode, it is discharged from the smoothing circuit. Since the amount of discharged electricity in this case is I/n of the amount of charged electricity, the power loss in the smoothing circuit is small, and since the amount of discharged electricity is made into a constant voltage by the constant voltage circuit, the constant voltage circuit However, there is no large power loss in the transistors that make up the device, and the heat generation effect of the transistors can also be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a voltage conversion circuit according to an embodiment of the present invention,
Figure 2 is a circuit diagram showing a modification of the smoothing circuit in Figure 1;
The figure is a waveform diagram of voltages at various parts for explaining the operation of FIG. 1. A...Cutoff circuit, B...Smoothing circuit, C...
Constant voltage circuit, FR...full wave rectifier circuit, D2...Zener diode, TRI/transistor as first transistor switch means, TR2, TR3...transistor as second transistor switch means.

Claims (1)

[Claims] (1) A cutoff circuit that full-wave rectifies the AC power source and outputs it, and cuts off the full-wave rectified output when the full-wave rectified value exceeds the cut-off voltage; When the full-wave rectified output is given, the charging mode is set to charge the full-wave rectified output, and when the full-wave rectified output is cut off by the cutoff circuit, the discharge mode is set to the charging mode. An AC power supply characterized by comprising: a smoothing circuit that discharges with an amount of electricity 1/n of that in the mode; and a constant voltage circuit that constantizes the output of the smoothing circuit at a voltage lower than the discharge value of the smoothing circuit. voltage conversion circuit.