JPS6117118B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving circuit for a switching element suitable for use in, for example, an induction heating cooking apparatus, and is particularly designed to reduce unnecessary power loss.

2. Description of the Related Art Conventionally, an induction heating cooking apparatus as shown in FIG. 1 has been proposed. That is, in Figure 1, 1
shows an oscillator that oscillates a rectangular wave signal of, for example, 20 KHz. The output signal of this oscillator 1 is supplied to the base of an npn transistor 2 that constitutes a drive circuit, the emitter of this transistor 2 is grounded, and the The collector is the next winding 3a of the transformer 3.
The transformer 3 is connected to a power supply terminal 4 to which a positive DC voltage is supplied through the transformer 3, one end of the secondary winding 3b of this transformer 3 is grounded, and the other end of this secondary winding 3b is connected to a switching circuit through a resistor 5. A diode 7 is connected in parallel to the resistor 5, the cathode of the GCS 6 is grounded, and the anode of the GCS 6 is connected to a diode 8 for damper and a capacitor 9 for resonance. The anode of this GCS 6 is connected to one end of a heating work coil 10, and the other end of this work coil 10 is connected to the positive terminal of a DC power supply 12 via a high frequency blocking coil 11. The negative pole of this DC power supply 12 is grounded, and the connection point between the work coil 10 and the choke coil 11 is grounded via a capacitor 13. In Fig. 1, the switching element GCS6
In accordance with the on/off status of the work coil 10, a pot or the like placed on the work coil 10 is heated by induction. in this case
The GCS 6 is turned on by a positive pulse of, for example, a square wave signal supplied to the gate, and turned off by a negative pulse. The absolute level of this positive pulse and negative pulse is the power supply terminal 4.
Determined by the voltage supplied to the in general
The temperature-absolute voltage (positive voltage) characteristic of the switching element for the drive voltage used to turn on a semiconductor switching element such as a GCS is as shown in curve 6a in Figure 2A, and as the temperature rises, the voltage decreases. On the other hand, when the temperature is low, a relatively high voltage is required as the drive voltage, and the temperature-absolute voltage (negative voltage) characteristics for turning off semiconductor switching elements such as GCS are shown in Figure 2A. curve 6
As shown in Fig. b, as the temperature rises, a higher voltage of negative level is required to turn off the GCS. Furthermore, since a large current is passed through the heating work coil 10, when a large current is passed through the GCS 6, it is necessary to increase the drive voltage supplied to this gate.
In the conventional circuit as shown in FIG. 1, considering the above points, the driving voltage that is constantly supplied to the gate of GCS 6 is such that a sufficiently large current can flow through GCS 6, and the temperature of this GCS 6 is low. The voltage was set to be sufficient to turn on the GCS6 at times, and to turn off the GCS6 at high temperatures. For this reason, in a driving circuit for a switching element as shown in FIG. 1, unnecessary power loss occurs because the GCS and the like are not ideal elements.

In view of this point, the present invention is designed to improve unnecessary power loss during normal operation.

An embodiment of a driving circuit for a switching element according to the present invention will be described below with reference to FIG. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted. In this example, the output signal of the oscillator 1 that generates a 20 KHz rectangular wave signal is supplied as a carrier signal to the pulse width modulation circuit 14, and the pulse width modulation circuit obtained at the output side of the pulse width modulation circuit 14 is The emitter of this transistor 2 is grounded, and the collector of this transistor 2 is connected via the primary winding 3a of a transformer 3 to a power supply terminal 4 to which a positive DC voltage is supplied. The transformer 3 is provided with a secondary winding 3c and a tertiary winding 3d wound in the opposite direction and in the same direction as the primary winding 3a. In this case, for example, the number of turns of the secondary winding 3c and the tertiary winding 3d are made equal, and voltages with equal absolute levels and opposite polarities are obtained at one end of each of the secondary winding 3c and the tertiary winding 3d. Do as you like. One end of this secondary winding 3c is connected to a positive DC voltage to the first rectifier circuit 1.
5 to the collector of an npn transistor 16, and one end of this tertiary winding 3d is connected to the collector of the npn transistor 16 via a second rectifier circuit 17 that obtains a negative DC voltage and a resistor 18, and is made conductive by a negative trigger pulse. Connect to the cathode of SCR19. Further, the other ends of the secondary winding 3c and the tertiary winding 3d are grounded. In this case, positive and negative DC voltages with equal absolute values are obtained on the output sides of the first and second rectifier circuits 15 and 17, respectively.

Also, the emitter of the transistor 16 is connected to the anode of the SCR 19, and the connection point between the emitter of the transistor 16 and the anode of the SCR 19 is connected to the GCS 6.
Connect to the gate. In addition, a rectangular wave signal is supplied from the oscillator 1 to the base of the transistor 16, and
The GCS is supplied to the gate of the SCR 19, turns on the transistor 16 in the positive half cycle of the rectangular wave signal from the oscillator 1, and uses the positive DC voltage obtained at the output side of the first rectifier circuit 15 as the driving voltage.
In this negative half cycle, the SCR 19 is turned on, and the negative DC voltage obtained at the output side of the second rectifier circuit 17 is supplied to the gate of the GCS 6 as an off voltage. GCS6
The cathode of the GCS 6 is grounded, and the anode of the GCS 6 is connected to one end of the heating work coil 10 via the primary winding 20a of the current detection transformer 20. Connect the damper diode 8 to the connection point at one end.
and ground through a parallel circuit of a resonance capacitor 9. One end of the secondary winding 20b of this transformer 20 is grounded, and the other end of this secondary winding 20b is connected to the input side of, for example, a rectifier circuit 21 constituting a current detection circuit, and the output signal of this rectifier circuit 21 is It is supplied to the control terminal of the pulse width modulation circuit 14. In this case, the pulse width modulation circuit 14 has a pulse width modulation circuit on its output side having a width corresponding to the voltage value supplied to this control terminal.

Also, a temperature detection device 22 is placed close to the GCS 6. The output voltage-temperature characteristic of the temperature detecting device 22 has a substantially quadratic curve shape with the pole at 25 DEG C., as shown by the broken line in FIG. 2B. For this reason, this temperature detection device 22
Connect the thermistor and posistor in parallel as
As shown in the resistance value-temperature characteristic as shown in curve 22a in Figure 2B, the resistance value reaches its maximum at 25°C, and the temperature increases at this 25°C.
An element whose resistance value gradually decreases as the temperature decreases further and as the temperature rises above 25 DEG C. is used to obtain an output voltage as shown by the broken line in FIG. 2B. The output signal of this temperature detection device 22 is supplied to the control terminal of the pulse width modulation circuit 14.
The rest of the structure is the same as in FIG.

Since the present invention is configured as described above, when the output signal of the pulse width modulation circuit 14 has a small pulse width as shown in FIG. 4A, for example, a rectangular wave as shown in FIG. 4B is applied to the collector of the transistor 2. A signal is obtained, and a rectangular wave signal as shown in FIG.
and 17, a positive DC voltage Va and a negative DC voltage -Va of relatively small absolute level are obtained as shown by broken lines in FIGS. 4C and 4D, respectively. Also, the output signal of the pulse width modulation circuit 14, for example, FIG.
When the pulse width is large as shown in FIG. 5, a rectangular wave signal as shown in FIG. Rectangular wave signals as shown in C and D are obtained, and the first and second rectifier circuits 15
and 17, a positive DC voltage Vb and a negative DC voltage -Vb of relatively large absolute level are obtained as shown by broken lines in FIGS. 5C and 5D, respectively. Even when the pulse width of the output signal of this pulse width modulation circuit 14 is other, the positive and negative DC voltages of the absolute level corresponding to this pulse width are output from the first and second rectifier circuits 15 and 17 in the same manner as described above. Get on the side. Therefore, when the current flowing through the GCS 6 is constant and the temperature of the GCS 6 changes, the control terminal of the pulse width modulation circuit 14 has a substantially quadratic curve shape with the pole at 25°C as shown by the broken line in FIG. 2B. Since the control voltage is supplied and a pulse width modulation signal with a corresponding pulse width is obtained on the output side of the pulse width modulation circuit 14, the absolute level is applied to the output sides of the first and second rectifier circuits 15 and 17, respectively. As shown in FIG. 2C, the positive and negative DC voltages form a substantially quadratic curve with the pole at 25°C.

When the temperature of the GCS 6 is kept constant and the current flowing through the GCS 6 is gradually increased, a gradually increasing control voltage is supplied from the rectifier circuit 21 to the control terminal of the pulse width modulation circuit 14, and the voltage of the pulse width modulation circuit 14 is increased. Since a pulse width modulation signal with a pulse width corresponding to this can be obtained on the output side, the first and second rectifier circuits 1
5 and 17, respectively, have positive and negative DC voltages whose absolute levels gradually increase as shown in FIG. 2D.

Therefore, in the present invention, since the drive voltage supplied to the gate of GCS6 is changed according to the current flowing through GCS6, there is no problem even if the current flowing through GCS6 becomes large.
Compared to a system that always supplies a constant drive voltage corresponding to large currents to the gate of the GCS6, unnecessary power loss can be reduced.

In addition, in the present invention, as shown in FIG. 2C, the driving voltage supplied to the gate of the GCS 6 is set to a higher voltage as the temperature of the GCS 6 becomes lower than a predetermined temperature, for example, 25° C. The absolute level of the negative DC voltage that turns off the GCS6 is increased as the temperature rises above a predetermined temperature, for example, 25°C, so that the GCS6 can be turned on sufficiently regardless of temperature changes. It can be turned off sufficiently, and yet
It can be turned on sufficiently when the temperature of the GCS6 is low and turned off sufficiently when the temperature of the GCS6 is high.Compared to a device that supplies a constant drive voltage with a relatively high absolute level, unnecessary power loss is achieved. There are benefits that can be improved.

FIG. 6 shows another embodiment of the invention. In this figure, two pulse width modulation circuits are provided, and the on voltage and off voltage of the GCS are obtained in relation to the respective output signals of these two pulse width modulation circuits ₁₄₁ and ₁₄₂ . It is. That is, in FIG. 6, the output signal of the oscillator 1 is supplied as a carrier signal to the pulse width modulation circuits 14 ₁ and 14 ₂ , respectively, and the output signal of the pulse width modulation circuit 14 ₁ is applied to the base of the npn transistor 2 ₁ . The emitter of this transistor ₂₁ is grounded, and the collector of this transistor ₂₁ is connected to a power supply terminal ₄₁ to which a positive DC voltage is supplied via the primary winding _3a1 of the transformer ₃₁ , The other end of the secondary winding 3b ₁ of this transformer 31 is grounded, one end of this secondary winding 3b ₁ is connected to the anode of a diode _15a via a resistor, and the cathode of this diode 15a is connected to the gate of the GCS 6. Connect to. In this case, a positive drive pulse of a level corresponding to the pulse width on the output side of the pulse width modulation circuit ₁₄₁ is supplied to the gate of the GCS 6. Further, the output signal of the pulse width modulation circuit ₁₄₂ is supplied to the base of the NPN transistor ₂₂ , the emitter of this transistor ₂₂ is grounded, and the collector of this transistor ₂₂ is connected to the primary winding _3a2 of the transformer ₃₂ . The transformer 32 is connected to the power supply terminal ₄₂ to which a positive DC voltage is supplied through the transformer 32, and the other end of the secondary winding _3b2 of the transformer ₃₂ is grounded.
One end of this secondary winding _3b2 is connected to the cathode of a diode 17a, and the anode of this diode 17a is connected to the gate of the GCS6. In this case _{, the pulse obtained at one end of the secondary winding 3b 2 of the transformer 32 and the pulse obtained at one end of the secondary winding 3b 1 of the transformer} 31 are made to have substantially the same polarity. At this time again
A negative off-pulse having a level inversely proportional to the pulse width on the output side of the pulse width modulation circuit ₁₄₂ is supplied to the gate of the GCS 6. Further, the output signals of the rectifier circuits 21 are respectively supplied to the control elements of the pulse width modulation circuit ₁₄₁ , and the output signals of the rectification circuits 21 are supplied to the control terminal of the pulse width modulation circuit 142 via the phase inversion circuit ₂₃ , Also, a temperature detection device 22b is arranged close to the GCS 6. The temperature detection device 22b is designed to generate an output voltage that gradually decreases as the temperature rises, for example, as shown by the curve 6a in FIG. 2A. The output signal of this temperature detection device 22b is supplied to each control terminal of the pulse width modulation circuits ₁₄₁ and ₁₄₂ . The rest of the structure is the same as in FIG. 3.

In FIG. 6, in response to temperature changes in the GCS 6, a driving voltage is obtained on the output side of the diode 15a, which decreases as the temperature rises, as shown by the curve 6a in FIG. 2A. diode 1
On the output side of 7a, an off-state voltage is obtained whose absolute voltage increases as the temperature rises, as shown by curve 6b in FIG. 2A. Further, when the current flowing through the GCS 6 changes, an absolute voltage pulse corresponding to the current is obtained on the output side of each of the diodes 15a and 17a, as shown in FIG. 2D.

Therefore, it is easy to understand that the same effect as in FIG. 3 can be obtained in FIG. 6 as well.

It goes without saying that other semiconductor switching elements can be used in place of the GCS 6 in the above embodiment. Furthermore, it goes without saying that the present invention is not limited to the above-described embodiments, and can take various configurations without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a conventional switching element drive circuit, FIGS. 2, 4, and 5 are diagrams for explaining the present invention, and FIG. 3 is a diagram showing an example of a switching element drive circuit according to the present invention. FIG. 6 is a block diagram showing one embodiment of the drive circuit, and FIG. 6 is a block diagram showing another embodiment of the present invention. 1 is an oscillator, 2 is a transistor, 3 is a transformer, 6 is a GCS, 14 is a pulse width modulation circuit, 15
17 is a rectifier circuit, 20 is a current detection transformer, and 22 is a temperature detection device.

Claims (1)

[Claims] 1. A signal related to the output signal of a pulse width modulation circuit whose input is supplied with an oscillator output as a drive signal for a switching element that switches the current of a predetermined load. detecting the current flowing through the switching element or the temperature of the switching element by a detection means provided in association;
When the current detection signal increases or the temperature detection signal changes from normal temperature, the pulse width modulation circuit is controlled by the current detection signal or the temperature detection signal depending on the degree of the current increase or temperature change. A driving circuit for a switching element, characterized in that the voltage of the driving signal is increased.