JPS5856473B2 - Oscillation drive circuit for induction heating cooker - Google Patents

Description

[Detailed description of the invention] The present invention relates to an oscillation drive circuit for an induction heating regulator.

Conventionally, this type of circuit has been constructed as shown in FIG.

In this circuit. is an induction heating coil that forms a series resonant circuit with capacitor C8, and transistor Q1.
When transistor Q2 is turned on, a current flows to store energy in this series resonant circuit, and when transistor Q2 is turned on, a current flows to release the stored energy.

This causes induction heating coil L.

An alternating current flows through this coil.

Eddy currents are generated in a pot, etc. placed near the container to heat it.

The current in the series resonant circuit is detected by a current transformer CT, and is applied to phase detection circuits PD1 and PD2 according to polarity, and the rising portion of the waveform is detected.

Each of the detection signals is converted into a pulse signal through a differentiating circuit, and then applied to a monostable multivibrator MM12MM2, and then converted into a signal with a predetermined time width and applied to a drive circuit to control the transistor Q1Q2.

Here, the time width of the signal that drives transistors Q1 and Q2 is the monostable multivibrator MM12.
It is constant by time constant elements R1, C1 and R2, C2 of MM2.

However, these elements, especially capacitors C1 and C
2 has a large variation in its capacitance value, and as a result, the drive times of transistors Qt and Q2 become different, and the temperature rise of one of transistors Q1-Q2 or the element characteristics (
There is a problem that there is an irregularity in the current due to Tstg), and there is wide variation in output depending on the product.

Therefore, an object of the present invention is to provide an oscillation drive circuit for an induction heating cooker that can drive a transistor for controlling current flow of an induction heating coil at a desired constant value.

In order to achieve this object, the present invention has an oscillation drive circuit for an induction heating cooker that uses a single circuit to determine the time width of a signal for driving a transistor for controlling energization of an induction heating coil. .

An embodiment of the present invention will be described below with reference to FIGS. 2 to 5.

FIG. 2 shows the circuit configuration of an embodiment of the present invention.
A single monostable multivibrator MM is used to determine the time width of the drive signal of the transistors Q, Q2, and the outputs of the phase detection circuits PD1 and PD2 are connected to the single monostable multivibrator MM through an exclusive OR circuit E-OR. The output of the monostable multivibrator MM is applied to a drive circuit via AND circuits AND1 and AND2.

The other circuit configurations are similar to the circuit shown in FIG.

FIG. 3 shows waveforms of various parts of the circuit of FIG. 2, and the operation of the circuit of FIG. 2 will be explained based on these waveforms.

1 coil L.

When the series circuit of C6 and C6 is energized, this is detected as i by the current transformer CT and is applied to the phase detection circuits PD1 and PD2.

The detection signal i of the current transformer CT is a sine wave, and if the phase detection circuit PD1 detects a half wave of positive polarity, PD2 detects a half wave of negative polarity.

Each polarity phase signal a', a'' detected by these phase detection circuits PD1 and PD2 is a rectangular wave signal that rises at the same time as the signal i rises and has a duration shorter than half the wavelength thereof.

These outputs a'. a” is the it and circuit AND1.
It is applied as an input to each one of AND2, and is also applied to an exclusive OR circuit E-OR after passing through a differentiating circuit.

What is given to the exclusive OR circuit E-OR is a pulse signal corresponding to the rise of the signals a', a'',
Only when either one of the signals is given, an output is given to the monostable multivibrator MM to trigger it.

The monostable multivibrator MM generates a signal a with a time width determined according to a time constant determined by a variable resistor 1 and a capacitor C8 every time a trigger is applied, and an AND circuit A
ND1. Give it as the other input to AND2.

In this case, the variable resistor VR is set taking into consideration that the time width determines the drive current conduction time of the transistors Q, Q2.

AND circuit AND1. AND2 is the output a of the monostable multivibrator MM and the phase detection circuit PD1. Depending on the logic conditions of the outputs a' and a'' of PD2, the signals S and C, respectively.
form.

This signal. C has the same time width as the output a of the monostable multivibrator MM, and the positive of the detection signal i of the current transformer CT;
It occurs at the rising edge of each negative half-wave.

That is, the signals b+c become signals having exactly the same time width, and as a result, the drive times of the transistors Q1 and Q2 are always constant.

FIG. 4 shows an example of the configuration of the above phase detection circuit.
The waveforms of each part are shown in FIG.

This circuit will be explained based on its operation.

When a positive half-wave signal i is applied to the base of one transistor Q, its collector signal p becomes zero, and when a negative half-wave is applied, this signal p becomes V+.

The polarity of this signal p is inverted by an inverter N1 to become a signal q, which is further differentiated to become a signal r, and a level detector DET detects a portion below Vd to obtain a signal S.

This signal corresponds to the signals a' and a'' in FIGS. 2 and 3.

As described above, the present invention uses a single circuit to determine the time width of the signal for driving the energization control transistor of the induction heating coil. A signal can be formed.

Further, when determining the time width, it is only necessary to adjust a single time constant element, and the work is simple.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an oscillation drive circuit of a conventional induction heating cooker, FIG. 2 is a circuit diagram of an embodiment of the present invention, FIG. 3 is a signal waveform diagram of each part of the circuit in FIG. 2, and FIG. 5A and 5B are a circuit diagram showing an example of the configuration of a phase detection circuit used in the present invention, and a signal waveform diagram of each part thereof. Lo...induction heating coil, Q...transistor.

Claims (1)

[Claims] 1 A series resonant circuit is constructed with an induction heating coil and a capacitor, and the positive value obtained by detecting the current flowing through this resonant circuit is
A first switching element inserted between the resonant circuit and the power source, a button, and a second switching element provided to short-circuit the resonant circuit using drive signals formed separately based on phase signals of each negative polarity. In an oscillation drive circuit for an induction heater, which controls on/off switching elements of the induction heater and supplies positive and negative sinusoidal currents to the coil, a signal obtained by differentiating the positive and negative polarity phase signals, respectively, is used. An exclusive OR circuit as an input, a monostable multivibrator that receives the output of this exclusive OR circuit as an input and forms a drive signal of a predetermined time width, and the output of this monostable multivibrator and the positive and negative polarity phase signals. A pair of AND circuits each of which has one polarity among them is provided as an input, and a pair of drive circuits that individually control on/off of each of the switching elements based on the output of the pair of AND circuits. An oscillation drive circuit for an induction heating regulator.