JPH06245524A - Power device - Google Patents

Abstract

PURPOSE:To provide a power device, in which jumping is not generated at both end voltage of load and the reliability of an element is improved while noises are reduced. CONSTITUTION:A power device has a switching circuit 2 switching input AC voltage by frequency higher than the frequency of input AC voltage and supplying load 6 having a resistance component and a reactance component with switched input AC voltage, a load-current detecting means 18 detecting the polarity of load currents and a free wheel circuit 7 making currents by the counter electromotive force of load 6 at the time of the off of the switching circuit 2 flow back by synchronizing switching elements 10, 11 connected in parallel and in complementary relationship with the polarity of load currents and on-off controlling the switching elements alternately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, a refrigerator and the like, and a load has a resistance component and a reactance component including a capacitive reactance and an inductive reactance. The present invention relates to a power supply device that supplies electric power.

[0002]

2. Description of the Related Art As a conventional power supply device for generating AC voltages having different effective voltages from an AC input power supply, there is, for example, one shown in FIG. In the figure, 1 is an AC power supply, 2 is a switch circuit, and is composed of a rectifying diode bridge 3 and a switching transistor 4. 5
Is a control circuit thereof, 6 is an AC load such as a motor, 7 is a freewheel circuit, and a freewheel diode 8,
9 and complementary free wheel transistors 10 and 11 as switching elements. 1
Reference numerals 2 and 13 are base current supply resistors, and 14 and 15 are bleeder resistors. To explain the operation of this device, the pulsating current rectified in one direction by the rectifying diode bridge 3 is switched by the switching transistor 4 at a frequency higher than the power supply frequency and at a certain on / off ratio (hereinafter referred to as duty ratio). Is supplied to the load 6. As a result, the voltage applied to the load 6 is changed so that the effective voltage decreases. At this time, when the load 6 contains a component other than pure resistance, the freewheel circuit 7 is provided as a path for flowing the current of the counter electromotive force generated in the load 6 when the switching transistor 4 is turned off. ing.
That is, of the potentials at points A and B of the AC input terminals of the diode bridge 3, when the potential at point A is somewhat higher than that at point B, the freewheel transistor 11 turns on, and the potential at point B goes to point A. When it is larger than a certain amount, the free wheel transistor 10 is turned on, and the current due to the counter electromotive force of the load 6 is circulated.

[0003]

In the conventional power supply device,
Since ON / OFF of the freewheel transistor operates by the voltage difference between the AC input terminals of the diode bridge, the AC load has a resistance component, a capacitance component, and an induction component,
If these components change from moment to moment, the phase of the load current will lag or lead the phase of the power supply voltage, and the current due to the back electromotive force of the load will flow smoothly during the lead period or lag period. Is not possible, and the voltage between both ends of the load will jump up, and there is a possibility that a voltage higher than normal will be applied to the element and the element will be destroyed.
Alternatively, even if the element is not destroyed, there is a problem that a voltage jump causes noise to occur. This will be further described with reference to FIGS. 7 and 8. In FIG. 7, in the case where the polarity of the AC voltage from the AC power source 1 is higher at the point C than at the point D only in a half cycle, and the switching transistor 4 is in the ON state and the load 6 is supplied with power. The elements required for the above are extracted from FIG. 6 and considered. In FIG. 7, the potential between points A and B is V _f 2 of the diode bridge 3 and the switching transistor 4.
_Is the sum of V _ce . Therefore, a minute base current is supplied to the freewheel transistor 11 via the resistor 13. Depending on the potential between the points A and B and the ratio of the resistance 13 to the resistance 15, the freewheel transistor 11 can be divided into the ON state or the state where only the base current is supplied. Next, when the switching transistor 4 is turned off, FIG.
The input AC voltage and load 6 are applied between points A and B.
The voltage due to the counter electromotive force is suddenly applied, the free wheel transistor 11 is turned on, and the current due to the counter electromotive force of the load 6 is circulated as indicated by the arrow in FIG. When the input AC voltage has the opposite polarity, the complimentary wheel transistors 10 arranged complementarily perform the same operation. In this way, the current due to the back electromotive force of the load is circulated.However, when the phase of the load current is delayed or advanced from the phase of the power supply voltage, the polarity of the power supply voltage has already been reversed. Instead, the load and the current try to flow as they were in the previous state, and the freewheel operation does not work properly. A when the switching transistor 4 is turned off
Even when the potential between the point and the point B is generated only to the extent that the freewheel transistor cannot be turned on, the freewheel transistor does not operate normally, and as a result, the voltage across the load jumps up. FIG. 9 shows the respective waveforms of the input AC voltage ((a) in the figure), the load current ((b) in the figure) and the voltage across the load ((c) in the figure) at this time.

Therefore, an object of the present invention is to provide a power supply device which does not cause a jump in the voltage across the load, improves the reliability of the element, and has less noise.

[0005]

In order to solve the above problems, the present invention provides a switch circuit for switching an input AC voltage at a frequency higher than its frequency and supplying it to a load having a resistance component and a reactance component, and the load circuit. A load current detection unit that detects the polarity of the flowing load current and a complementary switching element that are connected in parallel are provided, and the complementary switching element is synchronized with the polarity of the load current detected by the load current detection unit. And a freewheel circuit for causing a current to flow back due to the counter electromotive force of the load when the switch circuit is turned off.

[0006]

In the above structure, the load current detecting means detects the polarity of the load current, and the complementary switching elements in the freewheel circuit are synchronized with the polarity of the load current, that is, in synchronization with the phase of the load current. By being alternately turned on and off, the current path due to the back electromotive force of the load is not closed and the voltage jump across the load does not occur.

[0007]

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

1 and 2 are views showing a first embodiment of the present invention. It should be noted that, in FIG. 1 and the drawings showing each embodiment described later, the same or equivalent devices and elements as those in FIG. 6 are denoted by the same reference numerals as those used above, and the duplicated description will be omitted. In FIG. 1, although a switching IGBT 4 is used as a switching element in the switch circuit 2 in this embodiment, a transistor or FE is used.
It doesn't matter even with T. Similarly, the switching elements in the freewheel circuit 7 are also composed of freewheeling IGBTs 10 and 11 having a complementary relationship, but transistors or FETs may also be used. Reference numeral 16 is a drive circuit for the free wheel IGBT 10, and 17 is a free wheel I.
A drive circuit for the GBT 11 and a load current detection circuit 18 as a load current detection means for detecting the polarity of the load current flowing through the load 6. The free wheel IGBTs 10 and 11 which are complementary to each other by outputting a drive signal having the same pulse width as the synchronization of the input AC voltage from the circuit 16 or 17
Are alternately controlled to be turned on and off. 19
Is a load voltage detection circuit.

Next, the operation of the power supply device according to this embodiment will be described.
This will be described with reference to the timing chart of FIG. The pulsating current rectified in one direction by the rectifying diode bridge 3 is switched by the switching IGBT 4 at a frequency higher than the frequency of the input AC voltage (FIG. 2 (a)) and at a certain duty ratio, so that power is supplied to the load 6. Supplied. When the polarity of the load current (FIG. 2 (b)) is detected by the load current detection circuit 18 and the current flows from the upper part to the lower part in the figure with respect to the load 6, only the freewheel IGBT 11 is driven to be turned on. A signal is sent to the circuits 16 and 17. On the other hand, when a current starts to flow from the lower part to the upper part in the figure for the load 6, the free wheel IGBT 11 which has been in the on state until then is turned off and the free wheel IGBT 10 is turned on instead. Circuit 16,
A signal is sent to 17. As a result, the complementary freewheeling IGBTs in the freewheeling circuit 7 are provided.
10 and 11 are alternately turned on / off in synchronization with the polarity of the load current, that is, in synchronization with the phase of the load current (FIG. 2 (c),
(D)) It is prevented that the current path due to the back electromotive force of the load 6 is closed and the voltage across the load 6 jumps up.

FIG. 3 shows a second embodiment of the present invention. This embodiment detects a change in the polarity of the load current with a load current detection resistor or the like and has a complementary relationship with the freewheel IGBT.
The T is switched on and off. In the figure, 20 is a load current detection resistor, 21 is a load current polarity detection comparator, and 22 is a voltage conversion circuit. The H and L level outputs from the load current polarity detection comparator 21 are output as L and H level signals. Convert to. Reference numeral 23a is a light emitting side of the optical transmission element, and 23b is a light receiving side of the optical transmission element. The operation of this embodiment will be described. When a current flows from point E of the load current detection resistor 20 toward point F,
The output of the load current polarity detection comparator 21 becomes L level, and the output G point of the voltage conversion circuit 22 becomes H level.
At this time, the free wheel IGBT 10 is turned off by the drive signal from the drive circuit 16, and the optical transmission element 23
a emits light, sends a signal to the light receiving side 23b, and turns on the free wheel IGBT 11 via the drive circuit 17. On the contrary, when a current flows from the F point to the E point of the load current detection resistor 20, the freewheel IGBT 11 is turned off in the course opposite to the above, and the freewheel IGBT is turned off.
T10 turns on.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, the load current detecting optical transmission element detects a change in the polarity of the load current and controls the ON / OFF of the complementary freewheeling IGBT. In the figure, 24a and 25a are the light emitting sides of the load current detecting optical transmission elements, and 24b and 25b are the light receiving sides of the respective load current detecting optical transmission elements. Then, depending on the polarity of the load current, the light emitting side 24a of the optical transmission element for detecting the load current
Alternatively, a current flows through either one of 25a and 25a, and the light receiving side 24b
Alternatively, a signal is transmitted to 25b, and only one of the freewheel IGBTs 10 and 11 is turned on via the drive circuits 16 and 17.

FIG. 5 shows a fourth embodiment of the present invention. In the present embodiment, the polarity of the load current is detected by the current transformer, and the complementary freewheeling IGBT is switched on / off. In the figure,
A current transformer 26 is connected in series with the load 6. Other configurations and operations are almost the same as those of the second embodiment.

[0013]

As described above, according to the present invention,
The load current detecting means detects the polarity of the load current flowing through the load having the resistance component and the reactance component, and turns on the switching elements in a complementary relationship connected in parallel in the freewheel circuit in synchronization with the polarity of the load current.・ By controlling off, the current due to the back electromotive force of the load is circulated when the switch circuit is off, so the complementary switching elements are alternately turned on and off according to the phase of the load current, The current path due to the back electromotive force is not closed to cause the voltage across the load to jump, so that the reliability of the element can be improved and the generation of noise can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power supply device according to the present invention.

FIG. 2 is a timing chart showing voltage waveforms and current waveforms of respective portions and on / off timings of switching elements in the circuit of the first embodiment.

FIG. 3 is a circuit diagram of essential parts showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram of essential parts showing a third embodiment of the present invention.

FIG. 5 is a circuit diagram of an essential part showing a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional power supply device.

FIG. 7 is a partial circuit diagram for explaining the problems of the conventional example.

FIG. 8 is a partial circuit diagram for explaining a problem of the conventional example.

FIG. 9 is a waveform diagram of an input AC voltage, a load current, and a voltage between both ends of the load, showing the problems of the conventional example.

[Explanation of symbols]

1 AC power supply 2 Switch circuit 4 Switching IGBT 6 Load 7 Freewheel circuit 10, 11 Freewheel IGBT (switching element) 18 Load current detection circuit (load current detection means)

Claims (1)

[Claims] 1. A switch circuit for supplying a load having a resistance component and a reactance component by switching an input AC voltage at a frequency higher than the input AC voltage, and a load current detecting means for detecting a polarity of a load current flowing through the load. The switch circuit has complementary switching elements connected in parallel, and the complementary switching elements are alternately turned on / off in synchronization with the polarity of the load current detected by the load current detecting means. A freewheel circuit that circulates a current due to the counter electromotive force of the load when the power supply device is turned off.