JPH01138966A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To eliminate rush current and improve reliability, by precluding the recovery current of a flywheel diode by a second switching element. CONSTITUTION:A DC-DC converter is constituted of a DC voltage power source 2, a smoothing capacitor 3, a main switching transistor(Tr) 4, a flywheel diode 5, a choke coil 6 and the like while the induced voltage output thereof is supplied to a load 8. Further, the DC-DC converter is equipped with first and second voltage surge absorbing circuits 11, 12 other than the control circuit 10 of the main transistor 4. In this case, a second transistor 13 is connected in series to the flywheel diode 5 and is constituted so as to effect switching operation synchronizing with the switching operation of ON-OFF of the main Tr 4. According to this constitution, the second Tr 13 is put OFF when the main Tr 4 is put ON whereby a forward current, being conducted through the flywheel diode 5, may be intercepted and recovery current will never be conducted even when the load 8 is big.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surge suppressor circuit using a chopper-type Gilter switching element f as a DC-DC converter.

(Conventional extraction technique) Conventionally, DC-[
') C converter is known. This kind of DC-DC
Generally, a converter converts the voltage into a pulse voltage and then boosts the voltage using a transformer, a choke coil, etc., and a chopper type regulator is known as a DC-DC converter using the above-mentioned choke coil.

Here, an example of the DC-DC converter of this chopper type regulator will be explained using FIG. 3. In the figure, 1a and 1b are supply terminals of a DC voltage power source 2, and 3 is a DC voltage power source 2 supplied through the supply terminals 1a and lb.
4 is a main switching transistor (first switching element) that converts the voltage of the smoothed DC voltage power source 2 into a pulse voltage; 5 is a flywheel diode; When the switch is turned off, current flows through the load 8 due to the induced voltage output of the choke coil 6. Further, the choke coil 6 and the output capacitor +j7 have a function of smoothing the output voltage of the main switching transistor 4.

Further, the load 8 is connected to output terminals 9a and 9b, and is supplied with a voltage smoothed by the choke coil 6 and output capacitor 7. 1
0 is a control circuit that controls switching of 1 switching transistor 4, 11 is a resistor 11a and a capacitor 11b
A first voltage surge absorption circuit consisting of a diode 11C and a diode 11C is connected in parallel to the main switching transistor 4 to absorb the surge voltage generated in the main switching transistor 4. 12 is a second voltage surge absorption circuit consisting of a resistor 12a and a capacitor 12b, which is connected in parallel to the flywheel diode 5 to absorb the surge voltage generated in the flywheel diode 5. It has become.

Regarding the need to absorb high voltage surges in the voltage surge absorption circuits 11 and 12, the main switching transistor 4
1 switching transistor 4 and flywheel diode 5 due to the surge voltage generated when
This is because there is a possibility that the main switching transistor 4 and the flywheel diode 5 are destroyed, and even if the main switching transistor 4 and flywheel diode 5 are not destroyed, the surge voltage causes noise generation.

Next, the operation of the above-mentioned chopper type regulator will be explained.

First, when the voltage of the DC voltage power supply 2 is supplied to the supply terminals 1a and 1b, the main switching transistor 4 performs an ON-OFF switching operation in response to a switching control signal (drive signal) from the control circuit 10. , converts the voltage of the DC piezoelectric 12 into a pulsed voltage. This pulsed voltage is smoothed by a choke coil 6 and an output capacitor 7, and is output to output terminals 9a and 9b as a DC voltage. That is, the main switching transistor 4
When turned on, the load 8 is supplied from the DC power 8-power 11M2 via the main switching transistor 4 and the demix coil 6.
Current flows through the main switching transistor 4, and the main switching transistor 4 turns off.
Then, an induced voltage is generated in the choke coil 6, and a current flows through the flywheel diode 5 to the load 8 due to this induced voltage.

In other words, one switching transistor 4 is 0N-OFF.
Since current flows through the load 8 during both periods, the voltage supplied to the load 8 by the main switching transistor 4 is averaged. As a result, the control circuit 10 controls the duty ratio of the pulse width of the ON-OFF switching waveform of the main switching transistor 4, thereby increasing the output terminal 9a.

The DC voltage output to 9b can be adjusted.

However, in the above-mentioned chopper type regulator, when the main switching transistor 4 is turned on from OFF, the flywheel diode 5 changes from a conductive state to a reverse biased state in a short period of time, and is A short circuit occurs, and as shown in FIG. 4, an excessive reverse current (recovery current) flows from the DC voltage power supply 2 through the main switching transistor 4 to the flywheel diode 5, and this recovery current causes noise generation. It was causing this.

Furthermore, as a solution to this recovery current, it has been proposed to improve the inherent characteristics of the flywheel diode 5, but the recovery current of the flywheel diode 5 increases as the forward current increases.
There was a problem in that the larger the impedance of the load 8, the larger the recovery current, and the accompanying increase in noise generation.

(Objective of the Invention) The present invention solves the above-mentioned problems, and by blocking the recovery current flowing through the flywheel diode, it reduces noise and improves the safety and reliability of the circuit. The purpose of this invention is to provide a chopper type regulator DC-DC converter that can perform

(Structure of the Invention) The present invention provides a DC voltage power source, a load to which current is supplied by the DC voltage power source, and one line of a two-wire line connecting the DC voltage power source and the load. The first one is connected in series and converts the voltage from the DC voltage power source into a pulsed voltage.
a switch element, a choke coil connected in series to the first switch element and smoothing the converted pulsed voltage, and a cathode connected to a connection point between the first switch element and the choke coil, a flywheel diode whose anode is connected to the other line of the two-wire line and supplies current to the load when the first switch element is turned off; The DC-DC converter includes a control circuit that converts a voltage from a voltage power source into a pulsed voltage and generates a DC voltage to the load, the first switching element being connected in series with the flywheel diode, It is equipped with a second switch element that turns off when ONL.

According to the above M4 precept, when the first switch element turns on, the second switch element turns off, cutting off the forward current flowing through the flywheel diode and increasing the Ω load, that is, the impedance. Even if it is small, noise can be reduced because no recovery current flows.

(Example) FIG. 1 shows a circuit configuration of an embodiment of the present invention.

In this figure, a pnpt-transistor of a second switching element 13 is connected in series with the flywheel diode 5 of the embodiment shown in FIG. 3, and this second switching element F
13 is configured to perform a switching operation in synchronization with the ON-OFF switching operation of the non-transistor of the first switch element 4, and when the first switch element 4 is ON, the second switch element ? 13 is 0FFL, 1st
When the switch element 4 is OFF, the second switch element 13 is turned ON.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, when a HIGH (hereinafter referred to as HIT) is output as a drive signal from the control circuit 10, the first switch element "F4" is turned on, and the second switch element 13 is turned on.
FFL, current flows from the DC voltage power supply 2 to the load 8 via the first switch element 4 and the choke coil 6.

Next, when the drive signal from the control circuit 10 becomes LOW (L'' in the following description), the first switch element 4 turns OFF and the second switch element J'13 turns ON.At this time, An induced voltage is generated in the choke coil 6.

That is, the induced voltage is generated with positive polarity on the load 8 side of the choke coil 6 and negative polarity on the flywheel diode 5 side, so that the induced voltage is generated from the choke coil 6 to the load 8 and the second switch element? A current flows to the load 8 via the flywheel diode 5 and the flywheel diode 5 .

Further, when the drive signal from the control circuit 10 changes from "I L II" to "HII", the first switch element 4 is turned ON again.
Then, the output J voltage of the first switch element 4 is applied to the cathode side of the flywheel diode 5, but at the same time, the second switch element 13 is turned off, so as shown in FIG. Recovery current can be prevented from flowing through the flywheel diode 5.

Note that the first switching element f4 may be a pnpt-transistor, and the second switching element 13 may be an nDn transistor.

In this way, noise can be reduced by blocking the recovery current of the flywheel diode 5, which was the most important factor in the DC-DC converter of the chopper type regulator. An excessive rush current from the DC voltage power supply 2 can be prevented.

(Effects of the Invention) As described above, according to the present invention, since the flywheel diode coverage current is blocked by the second switch element, noise generation can be reduced. Furthermore, even when the load is large, noise generation due to the recovery current is eliminated, and therefore, there is no longer an excessive rush current from the DC voltage power supply corresponding to the recovery current as in the past, improving the reliability of the first switching element. can be achieved.

Note that one of the first switch element and the second switch element is composed of an npn transistor, and the other is composed of a pnp transistor.
By configuring the T-transistor and operating the first and second switch elements using the drive signal from the same control circuit, the switching of both switch elements can be reliably synchronized, which simplifies the circuit configuration. It is possible,
The number of parts can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a current waveform diagram of the flywheel diode of this embodiment, Fig. 3 is a circuit diagram of a conventional DC-OC converter of a chopper type regulator, and Fig. 4 is a circuit diagram of a DC-OC converter of a conventional chopper type regulator. The figure is a current waveform diagram of the flywheel diode of the DC-DC converter. 2... DC voltage power supply, 4... First switch element,
5... Flywheel diode, 6... Choke coil, 8... 4 loads, 10... Control circuit, 13...
-Second switch element. Patent applicant Matsushita Electric Works Co., Ltd. Representative Patent attorney Etsushi Kotani
Chief Patent Attorney 1) 1 Patent Attorney Ino Itaya Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A DC voltage power source, a load to which current is supplied by the DC voltage power source, and a load connected in series to one line of a two-wire line connecting the DC voltage power source and the load, a first switch element that converts voltage from a DC voltage power source into a pulsed voltage; a choke coil that is connected in series with the first switch element and smoothes the converted pulsed voltage; and a choke coil that smooths the converted pulsed voltage; a flywheel diode whose cathode is connected to the connection point between the switch element and the choke coil, whose anode is connected to the other line of the two-wire line, and which supplies current to the load when the first switch element is turned off; and a control circuit that supplies a drive signal to the first switch element and converts the voltage from the DC voltage power source into a pulsed voltage, and generates a DC voltage to the load.
- A DC-DC converter comprising a second switch element connected in series to the flywheel diode and turned off when the first switch element is turned on. 2. One of the first switch element and the second switch element is composed of an npn transistor, and the other is composed of a pn transistor.
The first and second
2. The DC-DC converter according to claim 1, wherein the switching elements are driven by the same control circuit.