JPH07105267B2 - Converter device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter device used in an induction heating cooker or the like for converting AC power of commercial frequency into high frequency power.

2. Description of the Related Art A conventional converter device of this type will be described with reference to FIG.

In FIG. 2, reference numeral 1 denotes a converter, a rectifier 5 connected through contacts of a switch 3 and a relay 4 connected in series to an AC power source 2, a load network 6 connected to the rectifier 5, Rectifier 5 connected to load network 6
It is composed of a transistor 7 which converts the direct current to a high frequency. Reference numeral 8 is a control circuit for controlling ON / OFF of the transistor 7, which includes a resistor 9 and transistors 10,1.
It is composed of a drive stage 13 of the transistor 7 composed of 1, 12 and a control stage 14 which outputs an on / off control signal of the transistor 7 to the drive 13 and controls the relay 4. Reference numeral 15 is a DC power supply for the control circuit 8, which is composed of a power supply transformer 16 connected to the AC power supply 2, a rectifying diode 17 connected to the secondary side thereof, and a smoothing capacitor 18.

The operation of the above configuration will be described. When the power is turned on,
That is, immediately after the switch 3 is turned on, first the DC power supply 15
Output voltage V ₀ rises to a predetermined power supply voltage Vcc, the control circuit 8 starts operating, and then the relay 4 is turned on by a signal from the control circuit 8 and the rectifier 5 through the load network 6 causes the transistor 7 to operate. A DC voltage is applied to. At this time, the drive stage 13 is driven by the signal from the control stage 14 of the control circuit 8.
Transistor 10 is conducting, and the gate-source voltage V _GS of transistor 7 is through transistor 12, the base-emitter voltage of transistor ₁₂ is V _BE12 , and the collector-emitter saturation voltage of transistor 10 is V _{CE (SAT). Ten}
Then, V _GC = V _BE12 + V _{CE (SAT) 10} (1), which is kept at an extremely low value, so that the transistor 7 does not conduct. Then, the oscillation of the transistor 7 is started by the activation signal given to the control stage 14 from the outside.

In the above description, the reason why the timing at which the DC voltage is applied to the transistor 7 by the relay 4 is delayed is that the parasitic capacitance 19 between the drain and gate of the transistor 7 is delayed.
This is to prevent the transistor 7 from being erroneously conducted. That is, since the rising of the output voltage V ₀ of the DC power supply 15 is charged to the smoothing capacitor 18, it is generally slower than the time from the application of the AC voltage to the rectifier 5 to the application of the DC voltage to the transistor 7. When the AC voltage is applied to the power transformer 16 and the rectifier 5 at the same time without using the relay 4, the DC voltage is applied to the transistor 7 when the output voltage V ₀ of the DC power supply 15 is still near 0V, and the drain of the transistor 7 is drained.・ The source voltage V _DS rises. In this case, the feedback current I _G passes through the parasitic capacitance 19 from the drain of the transistor 7 to the emitter of the transistor 12,
Base of transistor 12, resistor 9, smoothing capacitor 18,
Since the current flows through the source path of the transistor 7, even if the smoothing capacitor 18 has a sufficiently large capacitance, the resistance value of the resistor 9 remains unchanged.
If R ₉ and the current amplification factor of the transistor 12 are h _FE12 , then V _GS = V _BE12 + R ₉ · I _G / (1 + h _FE12 ) (2), the resistance value R ₉ of the resistor ₉ is large, and the feedback current I _G Is large, and the current amplification factor h _FE12 of the transistor 12 is small, the gate-source voltage V _GS of the transistor 7 becomes considerably larger than that of the equation (1) and exceeds the threshold voltage of the transistor 7, This is because 7 may be erroneously conducted and may be destroyed.

However, in the above-described conventional configuration, the relay 4 turns on / off the main current of the converter 1, so that it is necessary to use a large-sized and high-cost relay. It was difficult to reduce the cost.

The present invention solves the above problems, and provides a converter device capable of preventing erroneous conduction of transistors without requiring a relay for turning on / off a main current of a converter, and capable of downsizing and cost reduction. The purpose is.

Means for Solving the Problems In order to solve the above problems, the present invention provides a rectifier connected to an AC power source, a transistor for converting DC to a high frequency, and a load connected between the output of the rectifier and the transistor. A converter including a circuit network, a control circuit for driving the transistor on / off, a DC power source of the control circuit having a smoothing capacitor, an anode connected to the gate of the transistor, and a cathode output terminal of the DC power source. And a diode connected to the output of the control circuit and the gate of the transistor.

Action With the above configuration, when the output voltage of the DC power supply does not rise yet and is close to 0 V when the power is turned on, the DC voltage is applied to the transistor via the rectifier and the load network, and the drain-source voltage of the transistor Rises, and due to the parasitic capacitance between the drain and gate of the transistor, the feedback current flows from the drain of the transistor through the diode to the output end of the DC power supply, and at this time, between the gate and source of the transistor connected to the DC power supply and the control circuit. The voltage becomes the saturation voltage of the diode, the transistor does not operate, and erroneous conduction of the transistor is prevented. When the DC power supply rises, the clamp voltage of the diode becomes higher than the power supply voltage of the DC power supply, and even if the gate of the transistor is driven at the power supply voltage of the DC power supply or lower, the diode does not adversely affect the driving operation.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. The same components as those shown in FIG. 2 of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a circuit diagram of a converter device showing an embodiment of the present invention. In the converter device of the present invention, the relay 4 is deleted from the converter device shown in FIG. A diode 20 is provided, which is connected to the AC power supply 2 via only the anode, and whose anode is connected to the gate of the transistor 7 and whose cathode is connected to the output terminal of the DC power supply 15.

The operation of the above configuration will be described.

When the power is turned on, that is, immediately after the switch 3 is turned on, a DC voltage is applied to the transistor 7 via the rectifier 5 and the load network 6, and the drain-source voltage of the transistor 7 rises. At this time, the drain of the transistor 7
The feedback current I _G flows from the gate of the transistor 7 due to the parasitic capacitance 19 between the gates, but is absorbed by the smoothing capacitor 18 of the DC power supply 15 via the diode 20. Generally, when the voltage between the drain and source of the transistor 7 rises when the power is turned on, the output voltage V ₀ of the DC power supply 15 is still around 0V, so if the saturation voltage of the diode 20 is V _F20 , the gate-source of the transistor 7 The voltage V _GS becomes V _GS = V _F20 , and the gate-source voltage V _GS of the transistor 7 that is lower than that of the equation (1) is obtained, the transistor 7 does not conduct, and the cutoff of the transistor 7 is surely maintained. It After the drain-source voltage of the transistor 7 rises and stabilizes, the output voltage V ₀ of the DC power supply 15 rises and the power supply voltage V _{CC rises.}
Reach After that, the clamp voltage by the diode 20 becomes (V _CC + V _F20 ), which is higher than the power supply voltage V _CC of the DC power supply 15, so that the gate of the transistor 7 is driven between 0 and V _CC like the control circuit 8. However, the diode 20 does not have any adverse effect on its driving operation.

In this way, it is possible to prevent erroneous conduction of the transistor 7 when the power is turned on, and since the large-sized and high-cost relay 4 is not required, it is possible to reduce the size and cost of the converter device.

EFFECTS OF THE INVENTION As described above, according to the converter device of the present invention, the conventional power supply relay is used by making good use of the difference between the DC power supply of the control circuit when the power is turned on and the rise timing of the drain-source voltage of the transistor. Since the diode can prevent erroneous conduction of the transistor when the power is turned on without using the diode, the converter device can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a converter device showing an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional converter device. 1 ... Converter, 2 ... AC power supply, 5 ... Rectifier, 7
...... Transistor, 8 ...... Control circuit, 15 ...... DC power supply,
16 ... power transformer, 20 ... diode.

Claims (1)

[Claims] 1. A converter comprising a rectifier connected to an AC power supply and a transistor for converting DC to high frequency, and a load network connected between the output of the rectifier and the transistor, and a transistor for turning on the transistor. A control circuit for driving off, a direct current power supply of the control circuit having a smoothing capacitor, an anode connected to the gate of the transistor, and a cathode connected to the output end of the direct current power supply diode. A converter device in which an output is connected to the gate of the transistor.