JPS6387175A - power circuit - Google Patents

Abstract

PURPOSE:To reduce the cost of power circuit by detecting DC voltage obtained by rectifying AC input and switching a rectification mode to voltage doubler rectification or full-wave rectification mode according to said detected voltage value. CONSTITUTION:A power circuit is composed of a rectifier 1 constituting a bridge circuit, a photo-triac-coupler 2 having a switching function, a smoothing capacitor 4, a Zener diode 6 setting an operating voltage, a thyristor 7 and others. These rectifier 1, coupler 2 and capacitor 4 are so connected as to be subjected to voltage doubler rectification if power is applied to said photo-triac 2 and to fullwave rectification if power is not applied thereto. Thus, if both end voltage of the capacitor 4 becomes higher, the thyristor 7 is driven through the Zener diode 6 and a light-emitting part of the coupler 2 is put out to turn OFF the triac 2 and provide a rectifier circuit in a bridge full-wave rectification mode.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a power supply circuit, and particularly to a rectifier circuit that directly rectifies an AC input voltage such as a switching power supply.
The present invention relates to a power supply circuit that is effective in protecting equipment for use from erroneous connection to a 200V AC input.

[Conventional technology]

As a conventional device of this kind, for example, Japanese Patent Application Laid-Open No. 57-4
Devices described in Japanese Utility Model Publication No. 6675 and Japanese Utility Model Application Publication No. 57-99220 have been known.

These devices detect an AC input voltage and automatically switch between 100V and 200V by opening and closing a switch inserted between a bridge rectifier circuit and the midpoint of two smoothing capacitors.

[Problem that the invention seeks to solve]

However, the above-mentioned device requires a detection circuit for detecting alternating current voltage, and therefore has a problem in that the configuration becomes complicated.

That is, the device shown in the above-mentioned prior art can tolerate a sudden change in input voltage from 100V to 200V or a variation in input voltage from 8O to 240V.

The actual interlayer is 100V electric light line, 200V
It is extremely rare for the voltage of the power line to fluctuate by more than 20%, and when considering the cost of the function, it is possible to share the 100V system / 200V system without switching.
It's not a realistic answer.

The present invention was made in view of the above circumstances, and its purpose is to solve the above-mentioned problems in conventional power supply circuits and to be effective in protecting 100V equipment from incorrect connection to 200V AC input. The purpose of the present invention is to provide a low-cost power supply circuit.

[Means for solving problems]

The above object of the present invention is to rectify and smooth an AC input voltage,
A power supply circuit that outputs a DC voltage is provided with means for detecting the output DC voltage, a voltage doubler rectifier/smoothing circuit, a full-wave rectifier/smoothing circuit, and a means for switching between the two rectifier/smoothing circuits, and the switching means enables the above-mentioned Rectification/smoothing is performed by the voltage doubler rectifier/smoothing circuit when the detected voltage value of the detection means does not reach a certain value, and by the full wave voltage doubler circuit after the detected voltage value reaches the certain value. This is achieved by a power supply circuit characterized in that it is configured as a rectifier/smoothing circuit.

[Effect]

In the present invention, a DC voltage obtained by rectifying an AC input is detected, and the rectification method is switched from voltage doubler rectification to full-wave rectification based on this voltage value. , the DC voltage after rectification and smoothing is 2.8 times the input AC voltage (sine wave), and in a full-wave rectifier circuit it is 1.
Therefore, by appropriately setting the switching voltage value, it is possible to inexpensively realize a power supply circuit that is effective in protecting the above-mentioned 100V equipment from erroneous connection to the 200V AC input.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

The first Q is a configuration diagram of a power supply circuit showing an embodiment of the present invention. In the figure, 1 is a rectifier constituting a so-called bridge circuit, 2 is a photo-triac coupler having a switching function as described later, 3 is a balancing resistor, and 4
5 is a smoothing capacitor, 5 is a dividing resistor, 6 is a Zener diode that sets the operating voltage of this circuit, 7 is a thyristor, and 8 is the thyristor 7 and the photo triac.
A resistor is shown that limits the current flowing to the light emitting part of the coupler 2.

The above rectifier 1. The photo-triac coupler 2 and the smoothing capacitor 4 are connected so that when the photo-triac 2 is conductive, voltage double rectification is performed, and when it is not conductive, full-wave rectification is performed.

In addition, the voltage across the smoothing capacitor 4 is determined by the dividing resistor 5
．． It is connected to the gate of a thyristor 7 through a Zener diode 6, and the light emitting part of the photo-triac coupler 2 is connected so that it emits light when the thyristor 7 is conductive.

The AC input is connected to ACIN, and the output of this circuit is the voltage across the smoothing capacitor 4, and DCOUT
It is displayed. Generally, a switching regulator is connected after this stage.

FIG. 2 shows the operation of this circuit, and shows the output DC voltage (DCOυ) when an AC input (VAC) is connected to this circuit and the voltage is changed.

The operation of the circuit of this embodiment will be described below with reference to FIGS. 1 and 2.

When the input voltage is low, the light emitting portion current of the photo-triac coupler 2 is small, so the triac 2 is non-conductive, and the rectifier circuit operates as a bridge using the rectifier 1.

When the input voltage increases sequentially and the current of the light emitting part of the photo-triac coupler 2 increases, the current of the light-receiving part of the photo-triac coupler 2 increases accordingly, and the photo-triac 2 increases at point A in FIG. Conduct.

As a result, the rectifier circuit becomes a voltage doubler rectifier circuit, and the output DC voltage rapidly increases approximately twice.

Furthermore, as the voltage continues to rise, the AC input voltage increases to 100
The voltage reaches a dangerous level as a DC voltage (point B in FIG. 2), and the Zener diode 6 becomes conductive, causing the thyristor 7 to conduct.

When the thyristor 7 becomes conductive, the light receiving portion current of the photo-triac coupler 2 disappears, and the photo-triac 2 becomes non-conductive.

Therefore, the rectifier circuit becomes a bridge type again, and its output voltage becomes approximately 1/2.

Due to the latching operation of the thyristor 7, the rectifier circuit remains a bridge circuit even if the input AC voltage is reduced thereafter.

According to the above embodiment, the circuit automatic switching function for input voltages of 100V/200V can be achieved without using a complicated AC voltage detection circuit, so a power supply circuit with necessary and sufficient functions can be realized at low cost. effective.

The configurations shown in the above embodiments are merely examples, and it goes without saying that the present invention may use other components having similar functions.

〔Effect of the invention〕

As described above, according to the present invention, in a power supply circuit that rectifies and smoothes an AC input voltage and outputs a DC voltage, the output DC voltage detection means, a voltage doubler rectifier/smoothing circuit, and a full-wave rectifier/smoothing circuit are provided. A circuit and means for switching between the two rectification/smoothing circuits are provided, and the switching means performs the rectification/smoothing, and when the detected voltage value of the detection means does not reach a constant value, the voltage doubler rectification/smoothing circuit performs the rectification/smoothing. Furthermore, after the detected voltage value reaches the certain value, the full-wave rectification/smoothing circuit is configured to perform the operation, thereby providing an effective power source for protecting 100V equipment from incorrect connection to 200V AC input. This has the remarkable effect that the circuit can be realized at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power supply circuit showing one embodiment of the present invention, and FIG. 2 is a diagram showing the operation of this circuit. 1: Rectifier, 2: Photo triac coupler, 3:
Balancing resistor, 4: Smoothing capacitor, 5: Dividing resistor, 6: Zener diode, 7: Thyristor, 8:
resistance. −“)

Claims (1)

[Claims] 1. In a power supply circuit that rectifies and smoothes an AC input voltage and outputs a DC voltage, the output DC voltage detection means;
A voltage doubler rectification/smoothing circuit, a full-wave rectification/smoothing circuit, and switching means for the two rectification/smoothing circuits are provided, and the switching means performs the rectification/smoothing until the detected voltage value of the detection means reaches a constant value. A power supply circuit characterized in that the voltage doubler rectifier/smoothing circuit performs the voltage doubler rectification/smoothing circuit when the detected voltage value does not reach the constant value, and the full-wave rectifier/smoothing circuit performs the voltage rectification/smoothing circuit after the detected voltage value reaches the constant value.