JPH0619320Y2 - Common mode noise reduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a common mode noise reduction circuit in a switching regulator.

[Conventional technology]

The power supply section of a switching regulator that uses semiconductor switching elements has been made more efficient and smaller due to the excellent characteristics of the switching elements, but it controls high voltage ON / OFF at high speed, which causes high frequency noise. .

The noise contained in the output voltage and the noise applied between the terminals of the input power supply are both normal mode noise, and noise can be removed relatively easily by inserting an appropriate filter circuit, etc. to control noise troubles. Easy to do.

However, common mode noise generated between input and output, between input and case, between output and case, etc. is based on the imbalance of the line impedance from the input end to the load end, and the voltage level It is larger than normal mode noise and causes many noise problems.

Therefore, the noise source FET, the power transformer,
It is necessary to take noise removal measures for the rectifier circuit and its peripheral circuits.

FIG. 2 shows an example of a conventional common mode noise reduction circuit. Two capacitors connected in series are connected between the input side terminals of the primary side rectification circuit 104, and the middle point thereof is the case ground ( A common mode noise reduction capacitor 106 connected to the FG) and a capacitor equal in number to the secondary side rectification output circuit are connected in parallel to the connection line between the primary side of the power transformer 101 and the output side of the rectification circuit 104. In addition, one capacitor is connected to each one wire of all the secondary side rectified output circuits, and one capacitor is connected to the primary side and one capacitor is connected to the secondary side in series. The common mode noise reduction circuit 110 is composed of the same number of secondary side rectified output circuits as the number of secondary side rectified output circuits connected to the FG.

[Problems to be solved by the device]

Since the common mode noise reduction circuit 110 provided over the primary side and secondary side circuits of the power transformer requires twice as many capacitors as the number of secondary side rectified output circuits, the number of circuits increases. Then FG through the capacitor
Leakage current flowing to is also increased.

The increase in leakage current not only causes noise and trouble,
It is necessary to limit the safety of equipment and human body,
The selection of the number of capacitors and the capacitance used in the common mode noise reduction circuit had to solve the trade-off between the noise reduction effect and the increase in leakage current.

It is an object of the present invention to provide a common mode noise reduction circuit which solves the above-mentioned problems and reduces common mode noise in a switching regulator and has a small leakage current.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention is configured such that the primary side of a power supply transformer is composed of an FET having a control circuit and a rectifying circuit having a line filter and a common mode noise reduction capacitor. The secondary side of the transformer is a switching regulator composed of a plurality of rectification output circuits. In the switching regulator, one line connecting the primary side of the power transformer and the output side of the rectification circuit and a plurality of rectifications connected to the secondary side are provided. One capacitor of an appropriate capacity is connected to each line of the circuit, the ground lines of a plurality of capacitors connected to the secondary side are collected, and the ground line of the capacitor connected to the primary side is connected. It is connected to the FG all at once.

[Action]

According to the common mode noise reduction circuit of the present invention, since the number of capacitors connected to the primary side of the power transformer is only one, the number of capacitors including the capacitors connected to the secondary side is small and the ground wire is also used. Since it is shortened, the leakage current is reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

The primary side of the power transformer 1 is a FET equipped with a control circuit 3.
4 and line filter 5, and a rectifier circuit 4 including a primary-side common mode noise reduction capacitor 6, and a secondary side of the rectifier output circuit composed of a plurality of lines (three lines in this embodiment). There is.

The common mode noise reduction circuit according to the present invention is a grounding capacitor group provided across the primary side and the secondary side of the power transformer 1, and is a one-wire connecting the primary side of the power transformer 1 and the output side of the rectifier circuit 4. And one line of each line (three lines in this embodiment) of the secondary rectification output circuit, one capacitor of an appropriate capacity is connected,
This is a common mode noise reduction circuit 10 in which the ground lines of three capacitors attached to the secondary side line are collected and connected together with the ground line of one capacitor attached to the primary side to the FG. .

Primary side common mode provided on the input side of the rectifier circuit 4
The noise reduction capacitor 6 is the same as the conventional method,
In the common mode noise reduction circuit 10 between the primary and secondary sides of the power transformer 1 based on this invention, the number of capacitors used is smaller than that of the conventional method (the number of secondary side rectified output circuits-
Only 1) reduces by 2 in this example.

The capacitors to be reduced are all provided on the primary side of the power transformer 1, and when the AC power is supplied to the switching regulator, the capacitors form a leakage current circuit. The reduction effectively reduces the leakage current.

[Effect of device]

In the common mode noise reduction circuit according to the present invention, the number of capacitors on the primary side of the power transformer, which is effective for reducing the leakage current, is only one regardless of the number of the secondary side lines. In addition to the effect of reducing normal mode noise, there is the effect of reducing the number of capacitors and the cost due to the simplification of the accompanying ground circuit.

In addition, when multiple switching regulators receive power from the same AC power supply, if the leakage current of each switching regulator is large, the total value of the leakage current seen from the AC power supply will also increase, so the leakage current provided on the AC power supply side Although there was a drawback that the breaker became easy to operate, the switching regulator equipped with the common mode noise reduction circuit according to the present invention had a small leakage current, so it was necessary to change the set current value of the leakage breaker even when operating in parallel. There is also the advantage of not saying.

[Brief description of drawings]

FIG. 1 is a connection diagram of a switching regulator provided with a common mode noise reduction circuit showing an embodiment of the present invention, and FIG. 2 is a connection diagram of a switching regulator provided with a conventional common mode noise reduction circuit. Is. 1 ... Power transformer, 2 ... FET, 3 ... Control circuit, 4 ... Rectifier circuit, 5 ... Line filter, 6 ... Common mode noise reduction capacitor, 7, 8, 9 ... Secondary Rectification output circuit, 10 ... Common mode noise reduction circuit.

Claims (1)

[Scope of utility model registration request] 1. A primary side of a power transformer is composed of a FET having a control circuit and a rectifying circuit having a line filter and a capacitor for reducing common mode noise, and a secondary side of the power transformer is In a switching regulator composed of a plurality of rectification output circuits, each one of a line connecting the primary side of the power transformer and an output side of the rectification circuit and a plurality of rectification output circuits connected to the secondary side Each of the lines is connected to one capacitor of an appropriate capacity, the ground lines of the plurality of capacitors connected to the secondary side are collected, and the ground lines of the capacitors connected to the primary side are collectively packaged. Common mode noise reduction circuit characterized by connecting to body ground.