JPS5836471B2 - induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction heating device, and more particularly to a base drive circuit of a transistor type induction heating cooker.

Conventional Structure and Problems Conventionally, a transistor inverter device has been used as a high frequency power source for an induction heating cooker, and its base drive current is a substantially constant current with a small ripple component.

However, for household electrical equipment, the higher the power factor, the better, and the inverter device for induction heating cookers operates on almost full-wave DC voltage, and the waveform is usually modulated by the commercial power supply. Ta.

Therefore, near the zero voltage of the commercial power supply, the transistor is overdriven, resulting in disadvantages such as a particularly long turn-off time of the transistor and an increase in switching loss.

Keeping the ratio of collector current to base current constant improves the switching characteristics, so it is possible to modulate the base drive current in the same way as the voltage of the inverter circuit, but the transistor becomes non-conductive near the zero voltage of the power supply. This has disadvantages such as the oscillation stops or the base reverse current decreases, resulting in a longer turn-off time.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned drawbacks and realizes an induction heating device using a base drive circuit with low transistor switching loss.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a low frequency power source, a direct current power source comprising a rectifier connected to the low frequency power source and converting it into DC power, an induction heating coil that converts the DC power into high frequency power, and an induction heating coil. An inverter circuit including a power switching semiconductor connected in series with an oscillation control circuit that controls conduction of the power switching semiconductor of the inverter circuit and a pasted ? A drive current value supplied from the base drive circuit to the power switching semiconductor changes approximately in proportion to the input DC power waveform of the inverter circuit, and a low voltage power supply. In the vicinity of zero voltage, DC power is applied to the base drive circuit from the low voltage power supply.

DESCRIPTION OF EMBODIMENTS Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of an induction heating cooker according to the present invention, and FIG. 2 shows waveforms of various parts thereof.

Referring to FIG. 1, AC power is applied from a low frequency AC power source 1 to a rectifier 2 and converted into DC power.

An inverter circuit 3 is connected to the DC output of the rectifier 2 to convert DC power into high frequency power.

The oscillation of the inverter circuit 3 is controlled by an oscillation control circuit 4 and a base drive circuit 5.

DC power for the oscillation control circuit 4 that operates at a signal level is supplied from a low voltage power supply 6.

The residual voltage is also supplied to the base drive circuit 5 from the low voltage power supply 6 via the diode 7.

The output voltage of the rectifier 2 is applied to the base drive circuit 5 via a diode 50.

That is, the diode 7 and the diode 50 perform an OR operation, and the higher voltage of either one is supplied to the base drive circuit 5 to drive the power switching semiconductor 32.

The inverter circuit 3 includes a small-capacity input capacitor 30 connected to both ends of a DC power line, and a heating coil 31 and a power switching semiconductor 3 connected in parallel with the input capacitor 30.
Connect the two series connections.

For example, a transistor is used as the power switching semiconductor 32, and a resonance capacitor 33 button and a damper diode 34 are connected in parallel.

The base drive circuit 5 includes a switching transistor 51 controlled by the oscillation control circuit 4, a pulse transformer 52 connected to the collector of the switching transistor 51, and a pulse transformer 52 connected to the collector of the switching transistor 51.
It consists of a parallel connection body of a base resistor 53 and an anti-parallel diode 54 connected in series to the 2nd order.

A resistor 55 is connected in parallel between the base and the terminal of the power switching semiconductor 32.

The base drive circuit 5 includes a switching transistor 5
1 is in a conductive state, a forward base current is applied, and when it is turned off, the rebound voltage of the pulse transformer causes a reverse base current to flow through the power switching semiconductor 32, thereby speeding up the turn-off time and reducing switching loss.

In FIG. 2, A shows the output voltage Vin of the rectifier 2, and B shows the DC voltage vB of the base drive circuit 5.

The voltage E is applied from the low-voltage DC power supply 6 to the vicinity of zero voltage of the DC power supply VB, so it never becomes zero voltage, and the power switching semiconductor 32 is supplied with sufficient base forward current and base reverse current, so that the voltage near zero voltage However, the turn-off characteristics are quick, and problems such as stopping the oscillation of the inverter circuit 3 are eliminated.

FIG. 2C shows the collector voltage Vc of the power switching semiconductor 32.

Here, the B waveform in FIG. 2, that is, the base drive circuit 5
The relationship between the DC voltage VB and the collector voltage Vc of the power switching semiconductor 32 shown by the C waveform will be described in detail.

As mentioned above, the B waveform is a waveform in which the output voltage Vi of the rectifier 5 and the output voltage E of the low voltage DC power supply 6 are superimposed,
Although the power switching semiconductor 320 base drive current waveform is not shown, it has a similar waveform to the B waveform of and.

On the other hand, the DC power supply voltage Vi supplied to the inverter circuit 3 has a human waveform in Figure 2, and the voltage near the zero phase is very small, and when the aforementioned base drive current is applied, the power switching semiconductor near the zero phase becomes overdrive.

Then, the envelope of the collector current (collector voltage) is small even if the base drive is large when the supply voltage to the inharter circuit 3 is low, and the envelopes of the DC power supply voltage waveform Vi and collector voltage Vo are similar waveforms. becomes.

The low-voltage DC power supply 6 comprises the low-frequency AC power supply 1, a low-voltage transformer 60, a diode 61, and a filter capacitor 62.

The configuration of the low voltage DC power supply 6 is: As another method, for example, the output voltage of the rectifier 2 may be lowered by a resistor.

As described above, according to the present invention, the voltage of the base dry circuit 5 is approximately the same voltage as that of the inverter circuit 3, the ratio of the collector current to the base drive current of the power switching semiconductor 32 is kept approximately constant, and overdrive is prevented. It is characterized by low power consumption.

1. In addition, when the power supply voltage is near zero, the low voltage power supply supplies enough power to turn on and off the power switching semiconductors, the inverter circuit stops oscillating, and the cooking container heated by the heating coil makes noise. Alternatively, it is possible to eliminate disadvantages such as an increase in switching time of transistors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an induction heating device according to an embodiment of the present invention, and FIGS. 2A, B, and C are waveform diagrams of various parts thereof. DESCRIPTION OF SYMBOLS 1... Low frequency AC power supply, 2... Rectifier, 3... Inverter circuit, 4... Oscillation control circuit, 5... Base drive circuit, 6... Low voltage power supply, 31... Heating coil, 32... Power switching semiconductor, 33...
・Resonance capacitor.

Claims (1)

[Claims] 1. A low frequency power source, a DC power source connected to the low frequency power source and comprising a rectifier that converts it to DC power, an inverter circuit that converts the DC power to high frequency power and includes a power switching semiconductor connected in series with an induction heating coil. It consists of an oscillation control circuit that controls conduction of the power switching semiconductor of the inverter circuit, a base drive circuit, and a low voltage power supply, and the drive current value supplied from the base drive circuit to the power switching semiconductor is the input DC of the inverter circuit. It changes almost in proportion to the power supply waveform,
and an induction heating device that applies DC power to the base drive circuit from the low voltage power supply near zero voltage of the DC power supply.