JPS61249685A - Switching regulator - Google Patents

Abstract

PURPOSE:To decrease the peak value of rush current to a transistor by switching a limiting resistance circuit on a primary side by using a conductor which is operated by an electromagnetic coil in accordance with the detected secondary side voltage value thereby controlling the current. CONSTITUTION:The output voltage at both terminals of an output resistance 6a connected to output terminals A, B is detected by a voltage detector 7. The conductor MC is closed to short circuit the limiting resistor RA when the detected value exceeds the prescribed value. The current from an AC power source 1 is thereby acted in the direction to be admitted without limitation. The conductor MC is held open when the secondary output voltage is below the prescribed voltage. The resistor Ra is then acted in the direction where the current from the power source 1 is limited. The rush current is thus suppressed by the limiting resistor in the stage of throwing the switching of the transistor. The peak value is thereby kept low and the failure of the transistor is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a switching regulator for a PFM (variable frequency) type welding machine, and particularly relates to a switching regulator that prevents damage to transistors caused by a secondary smoothing capacitor. It is.

[Conventional technology]

A conventional switching regulator of this type has a configuration shown in FIG. In FIG. 2, reference numeral 1 denotes an external AC power source, and in FIG. 91, a two-phase AC power source is used as an example. 2 is a primary switch that opens and closes the AC power supply 1''Ik. 3 is a primary rectifier, to which AC power 1 is input when the secondary circuit breaker 2 is closed (when turned on); 3a is a smoothing capacitor connected in parallel to the above-mentioned -order rectifier 3 to smooth the converted DC power source. 4#: is converted into direct current by the -order rectifier 3. smoothing capacitor 3a. It is a transistor used as an inverter to convert smoothed and smoothed power into high-frequency alternating current; the collector and emitter are connected in series with a transformer T, and the transistor is transformed by alternately giving signals to its base. 4 is alternately on (ON) and off (OF
F) L, -order rectifier 3. It converts the DC output from the smoothing capacitor 3a into AC whose pulse width is controlled. The AC output obtained by this transistor 4IC is insulated by a transformer T and regulated to a predetermined voltage, and the AC output after this voltage regulation is rectified again by a secondary rectifier 5a and a flywheel diode 5b, and then Riak)
/L15 (!) and is smoothed by a large-capacity secondary smoothing capacitor 5d and outputs DC. This DC output is sent to terminals A and B to a welding machine (not shown) via an output resistor 6a.
06 outputted from the output resistor 6 outputs the voltage of the above DC output.
This is a control circuit that detects both ends of a and controls the transistor 4 based on the output.

FIG. 4 shows the control circuit 6 in FIG. 3 when the transistor 4 is turned on and off to start driving.
FIG. 3 is a state diagram showing the relationship between the current flowing in and time t.

The conventional switching regulator is configured as described above, and the control circuit 6 starts frequency control of the transistor 4 with a certain pulse width, and when the transistor 4t is turned on and off, and when it is turned on, the secondary smoothing capacitor 5d is
An excessive amount of charging current flows through the transformer T in a loop through the series circuit of the secondary rectifier 5a, the secondary reactor 5c, and the secondary smoothing capacitor 5d. This charging current is a voltage
The primary current of T appears as a very large pulse current. That is, as shown in FIG. 4, an inrush current that significantly exceeds the maximum rated current of the transistor 4 appears.

[Problem that the invention seeks to solve]

In the conventional switching regulator as described above, there is a problem that, when the transistor is turned on, the current flowing through the transistor may exceed the rated current value, which may damage the transistor.

This invention was made to solve this problem, and it suppresses the peak value of the pulse current (rush current) when the transistor is turned on, and prevents damage to the transistor by keeping the current flowing through the transistor below the rated current value. The purpose of this invention is to obtain a switching regulator that can perform

[Means for solving problems]

In the switching regulator according to the present invention, a limiting resistor is provided immediately after the transistor is turned on to limit the current flowing through the transistor, and a limiting resistor is provided in the voltage detector so that the output voltage on the secondary side reaches a predetermined voltage or higher. When the electromagnetic coil is driven, the conductor is closed, and this closing short-circuits the limiting resistor.

[Effect]

In the second aspect of the invention, the voltage detector detects the output voltage 1ts.
t, , ) Since the limiting resistor is enabled or disabled to suppress the inrush current to the transistor, damage to the transistor can be prevented.

〔Example〕

FIG. 1 is a block diagram of a circuit showing an embodiment of the present invention, and in FIG.
16a is the same as the same reference numeral in FIG. 2 in the figure, 7 is an output resistor 6 connected to output terminals A and B.
It is a voltage detector that detects the output voltage across KG of a, and monitors whether the output voltage exceeds a predetermined voltage.
An electromagnetic coil (not shown) is driven according to the monitoring result. RA is a limiting resistance that limits the current flowing from the AC power source 1 through the primary rectifier 3 and the transformer T to the transistor 4, and the conductor MC of the electromagnetic coil is connected in parallel, and when the contactor MC is closed, the control is performed. Resistor Ra is shorted.

In the switching regulator configured as described above, the secondary output voltage is detected by the voltage detector 7,
When this secondary output voltage is below a predetermined value, the conductor MC is opened and the limiting resistor Ra acts in the direction of limiting the current from the AC power supply 1, and when the secondary output voltage is above the predetermined value, The conductor MC is closed, the limiting resistor Ra is short-circuited, and the current from the AC power source 1 flows in without restriction. Therefore, when switching of the transistor 4 is started from the control circuit 6, the required current flows through the transistor 4, limited by the limiting resistor Ra, since the secondary output voltage does not reach the predetermined voltage immediately after the switching is started (turned on). After that, when the secondary output voltage becomes equal to or higher than the predetermined voltage, that is.

When the charging voltage of the secondary smoothing capacitor 5d becomes stable, the conductor MC is closed for the first time, the limiting resistor Ra is short-circuited, and a current flows through the transistor 4 without passing through the limiting resistor Ra. FIG. 2 shows the state of the current flowing through the transistor 4 in these initial states.

With the above, the control circuit 6 starts switching the transistor 4, and when the transistor 4 is running, the secondary smoothing capacitor 5
A steep charging current does not flow with respect to d, and therefore, the peak value of the second pulse current in the transistor 4 is much larger than the maximum rated current of the transistor 4, as is clear from FIG. Low 2 hit.

2. In the above embodiment, the limiting resistor 'Ra and the conductor M
Although C is provided on the input side of the primary rectifier 30, it may also be provided on the output side, and the same effect as in the above embodiment can be obtained. 19. In the above embodiment, the case where the AC power supply 1 is two-phase is shown, but it may be three-phase.

〔Effect of the invention〕

As described above, the present invention is as follows. When the transistor is switched on, the inrush current of the transistor is suppressed by the limiting resistor, and after the charging voltage of the secondary smoothing capacitor is stabilized, the limiting resistor is short-circuited to reduce the normal primary current. Since the current is configured to flow, the peak value of the inrush current of the transistor can be kept low by 2, and damage to the transistor can be prevented.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a switching regulator showing an embodiment of the present invention, Fig. 2 is a state diagram showing the relationship between current and time in the transistor shown in Fig. 1, and Fig. 3 shows a conventional switching regulator. The configuration diagram, FIG. 4, is a state diagram showing the relationship between current and time in the transistor of FIG. 3. In the figure, 1 is an AC power supply, 4 is a transistor, 5d is a secondary smoothing capacitor %T is a voltage detector, MC is a conductor, and Ra is a limiting resistor. 2. In each figure, the same reference numerals indicate the same or similar parts. 1: Compassionate power source 4: Tofu 7 si" Star Ra: Wisdom j limit I 6 anti-time t" Time 15llt Procedural amendment (voluntary)

Claims (1)

[Claims] In a switching regulator that performs variable frequency control without detecting the secondary current and is provided with a secondary smoothing capacitor on the secondary side, the output voltage on the secondary side is detected and compared with a predetermined voltage, and the result is A voltage detector that outputs,
An electromagnetic coil having a conductor that is opened or closed by the output of this voltage detector, and a limiting resistor that is short-circuited when the conductor is closed and limits the current from the external AC power supply to the primary transistor when it is open. 1. A switching regulator, characterized in that when the output voltage reaches a predetermined voltage when the transistor is turned on, the conductor is closed and the limiting resistor is short-circuited.