JPH0449858A - Dc power supply circuit - Google Patents

Abstract

PURPOSE:To reduce the high voltage noise to be applied to a rectifier bridge so as to improve the durability by high voltage noise by applying the voltage divided by capacitors to a rectifier bridge in the case where high voltage noise such as static electricity, etc., is applied to the output side. CONSTITUTION:In case that the pulse-shaped high voltage noise by static electric ity, etc., is applied to output side, it is applied directly to the output end on the side of a rectifier bridge 1 through capacitors C1, C2 and C3 and then it is transmitted to the ground of an AC power source 5 through this output end on the-side. High voltage noise is divided by the capacitors, and only the voltage of the capacitor C3 is applied to the output end of the rectifier bridge 1. Hereby, the durability of DC power supply circuit to high voltage can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an input/output isolated type DC power supply circuit having a transformer or the like, and particularly takes measures against high voltage noise such as static electricity.

[Conventional technology]

Conventionally, AC from an AC power supply is rectified by a rectifier bridge, inputted to the primary side of an isolation transformer, and switched by a switching transistor to excite voltage on the secondary side.
A DC power supply circuit is known that rectifies and smoothes this excitation voltage before outputting it.

That is, for example, as shown in FIG. 2, alternating current from an alternating current power supply 5 is rectified by a rectifying bridge 1, smoothed by a capacitor C2, and inputted to the primary coil of a transformer T. When this input voltage is switched by the transistor Q1, a voltage is excited in the secondary coil L2. This excitation voltage is rectified and smoothed by a diode D1 and a capacitor C4, and then output.

In such a DC power supply circuit, as a noise countermeasure, a capacitor C□ is connected between one side of the negative side coil L1 and one side of the secondary side coil L2, and an alternating current is connected between the primary side and the secondary side. This short circuit reduces the influence of inductive noise on the secondary side. Further, a coil L3 is connected to both ends of the output side of the rectifying bridge 1 in series with the capacitor C2 to prevent switching noise and the like from being transmitted to the rectifying bridge 1.

By the way, in this DC power supply circuit, when high voltage noise such as static electricity is applied to the output side, it is transmitted to the primary side of the transformer T through the capacitor C. At this time, since the impedance of the coil L3 against high voltage noise is high, the high voltage noise is not transmitted to the one side output terminal of the rectifier bridge 1, but is directly applied to the + side output terminal of the rectifier bridge 1 through the capacitor C2. Ru. If the applied voltage is equal to or higher than the withstand voltage of the rectifier bridge 1, the rectifier bridge 1 is dielectrically broken down and becomes short-circuited, and an overcurrent flows through the input protection elements 2 and 3, resulting in open-circuit breakdown.
This isolates the DC power supply circuit from the AC power supply.

[Problem to be solved by the invention]

However, in the above DC power supply circuit, since the high voltage noise is directly applied to the + side output terminal of the rectifier bridge 1, it is necessary to increase the withstand voltage of the rectifier bridge 1, and the shape of the rectifier bridge 1 is As the size increases, the cost also increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a DC power supply circuit that reduces high voltage noise applied to a rectifier bridge and improves durability against high voltage noise.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an input/output isolated type DC power supply circuit that rectifies input AC power with a rectifier bridge, further converts the input AC power into DC power, and outputs the DC power. A first capacitor and a coil are connected in series in this order to both ends of the output side of the rectifier bridge, and a second capacitor is connected to one side between the input and output insulation parts, and a second capacitor is connected to both ends of the output side of the rectifier bridge. 3 capacitors are connected, and the high voltage noise from the output side is divided by the first, second and third capacitors.

[Effect]

According to the DC power supply circuit configured as described above, the input from the AC power supply is usually rectified by the rectifier bridge, smoothed by the first capacitor, and then converted to DC power at the output side and output. On the other hand, when high voltage noise such as static electricity is applied to the output side, the high voltage noise is transmitted to the input side by the second capacitor. At this time, since the impedance of the coil with respect to high voltage noise is high, the high voltage noise is not transmitted to the one side output of the rectifier bridge 1, but is transmitted to the first and third capacitors. That is, the high voltage noise is divided by the first, second, and third capacitors, and the divided voltage carried by the third capacitor is applied to the rectifier bridge.

〔Example〕

FIG. 1 is a circuit diagram showing an example of a DC power supply circuit according to the present invention. ``The rectifier bridge 1 rectifies the alternating current from the alternating current power source 5 that is input through the input protection elements 2 and 3, and outputs it to the primary side film L1 of the insulation type transformer T. The input protection element 2.3 is opened and destroyed when an overcurrent flows, cutting off the rectifier bridge 1 side from the AC power supply 5 to protect the circuit.

The capacitor C□ short-circuits the primary and secondary sides in an alternating current manner and guides noise generated on the secondary side to the primary side. The capacitor C2 smoothes the rectified output from the rectifying bridge 1. The capacitor C3 is connected in parallel to the output of the rectifying bridge 1, and serves to divide, for example, pulse-like noise from the secondary side, together with the capacitors C1 and C2, and apply the divided voltage to the output end of the rectifying bridge 1. The coil L3 reduces the transmission of switching noise and the like to the rectifier bridge 1 through the one line on the primary side. The transistor Q switches the rectifying input input to the primary coil L1 to excite a voltage in the secondary coil L2. The control circuit 4 controls the switching of the transistor Q□.

The diode drawer and capacitor c4 rectify and smooth the excitation voltage of the secondary coil L2 and output the same.

Next, the operation of the DC power supply circuit having the above configuration will be explained.

The alternating current from the alternating current power source 5 is input to the rectifier bridge 1 through the input protection elements 2 and 3, where it is rectified, smoothed by the capacitor C2, and input to the primary coil L1 of the transformer T. On the other hand, the transistor Q1 is switched by the control circuit 4, and a voltage is excited in the secondary coil L2. This excitation voltage is rectified by diode D1 and capacitor C4
It is smoothed and output.

On the other hand, when pulse-like high voltage noise due to static electricity etc. is applied to the output side, the high voltage noise is caused by capacitor C□
, c2. It is applied directly to one side output terminal of the rectifier bridge 1 through c3, and is transmitted to the ground of the AC power supply 5 through this negative side output terminal.

At this time, the high voltage noise is caused by the capacitor C□.

The voltage is divided by C2 and C3, and only the divided voltage carried by the capacitor C3 is applied to the output terminal of the rectifier bridge 1.

That is, by increasing the capacitance of the capacitor C3, it is possible to lower the divided voltage of the high voltage noise to the output of the rectifier bridge 1.

On the other hand, if excessive high voltage noise is applied to the output side,
This excessive high voltage noise may cause malfunction or destruction of the control circuit 4 and other circuits (not shown) connected to the output side. As a result, control becomes uncontrollable, which impairs the functional safety of the DC power supply circuit. Therefore, the capacitance of the capacitor C3 is set so that the divided voltage of the capacitor C3 becomes equal to or higher than the withstand voltage of the rectifier bridge 1 when the excessively high voltage noise is output. That is, due to the application of excessive high voltage noise, the rectifier bridge 1 is dielectrically broken down and becomes short-circuited, and an overcurrent flows through the input protection element 2゜3, causing an open circuit breakdown and cutting off the rectifier bridge 1 side from the AC power supply 5. , to protect the circuit.

In this way, the capacitance of capacitor C3 or capacitor c1. By adjusting the voltage division ratio handled by C2 and C3, when the applied high voltage noise is relatively low, the rectifier bridge 1 can continue to operate normally without dielectric breakdown, and will not exceed the permissible level. If an excessively high voltage noise is applied, the rectifier bridge 1 undergoes dielectric breakdown first, and the input protection element 2.3 interrupts the circuit to protect other circuits.

〔Effect of the invention〕

In the present invention, when high voltage noise is applied to the output side due to static electricity or the like, the high voltage noise is divided by the first, second and third capacitors, and the third capacitor carries the divided voltage. is applied to the rectifier bridge, it is possible to improve the durability of the DC power supply circuit against high voltage noise. Further, since the second capacitor and the coil are used for noise reduction, and the first capacitor is used for smoothing, the circuit configuration of the DC power supply circuit can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a DC power supply circuit according to the present invention, and FIG. 2 is a circuit diagram for explaining the problem. 1... Rectifier bridge, 5... AC power supply, C□...
Capacitor (second capacitor), C2... capacitor (first capacitor), C3... capacitor (third capacitor)
capacitor), Ll...-next coil, Ll...
2i1B+1 coil, L3...coil, T...isolation type transformer.

Claims (1)

[Claims] 1. In an input/output isolated DC power supply circuit that rectifies input AC power with a rectifier bridge and then converts it to DC power and outputs it, there is a The first capacitor and the coil are connected in series in this order, and the - side between the input and output insulation parts is connected with a second capacitor, and a third capacitor is connected to both ends of the output side of the rectifier bridge, and from the output side A DC power supply circuit characterized in that high voltage noise is divided by the first, second and third capacitors.