JPS5848388A - Induction heating cooking device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating cooker, and more particularly to an induction heating cooker that uses a two-transformer automatic oscillator as a drive source of an inverter and has an input control circuit added thereto.

Conventionally, a method has been proposed in which a pulse transformer including a clock oscillator is used as a drive circuit for a high-frequency inverter including an induction heating coil. A step-down transformer is required, which increases the size and cost of the entire cooker.

The present invention eliminates the above drawbacks by using a two-transformer automatic oscillator as a drive source for switching elements constituting a high-frequency inverter, and further adds an input control circuit compatible with this automatic oscillator. . Embodiments of the present invention will be described in detail below based on the drawings.

In Figure 1, (1) is an AC power supply, (2) is a choke coil, (3) is a rectifier circuit, (C1) is a smoothing capacitor, and (Qt) (Q, *) are two transistors connected in series. , which acts as a unidirectional switching element. (4
) is a transistor (a resonant transistor connected in parallel to Q
A series resonant circuit consisting of a capacitor ((1) and an induction heating coil, (Dx) and (Dz) are transistors (Q,
1) (Q, is a diode connected in antiparallel to ri. The above transistor (Ql) (Q, meaning), series resonant circuit (4), and diodes (Dt) (Ds) form an inverter circuit (6). (CT) is an AC power supply (
1) A current transformer that detects the current flowing from (
6) are drive signals a and b of the transistor (Q, 1) (Q, goose).

Drive the inverter (5) with a control circuit that outputs c and d,
Control. Here, signals a and O are transistors (Qa
These are pulse signals of mutually opposite phases that are added to each pace of the transistors (Qz) (
Qx) is input to the emitter of the transistor (Q, +) (
1; The potential for the pace of h) is adjusted to ensure the operation. If the collector potential of the transistor (Ql) is set to vcc1 and the emitter potential of the transistor (Q is ground potential), then the transistor (Q>) (Q,!
), the series resonant circuit (4) has a potential V
Connected alternately between CC1 and ground.

In this series resonant circuit (4), when the resonant frequency and the drive frequency of the transistor (QS) are equal, the impedance becomes zero, the current waveform flowing through the induction heating coil υ becomes a sine wave, and each half becomes a sine wave. The transistor that handles the current changes every cycle.The series resonant circuit (4) is adjusted so that the oscillation frequency of the inverter circuit (5) is approximately 20KH2, and a control circuit made of ferrous metal is placed on the induction heating coil D. A pot (not shown) is placed nearby and heated by induction.

The control circuit (6) is constituted by a two-transformer self-excited oscillator, and a power supply voltage Vcc is applied via a diode (I), ). This voltage VCC is applied to a smoothing capacitor (Or
) is small in order to improve the power factor, so it draws a pulsating flow waveform that is hardly smoothed. (T1) is a first transformer in which two transistors (QIMQ, 4) having the same characteristics are connected complementary to each other, and each brefter winding 11 (nm) (na) constitutes its primary winding. Each transistor (Q, 1
) (C4) are commonly connected and connected to the midpoint of the primary winding via a smoothing capacitor (C3), and at the same time are connected to the power supply voltage VCC terminal via a diode (D3). (T2) is the second transformer, the pace winding (1ns) of the transistor (Qs) (Q,4)
)(na) constitutes its secondary winding. (R1)
(R) is the resistor inserted between the pace emitter of the transistor (Q, s) (Q, 4), (Rs) is the starting resistor, (D4) (C4) L3 is the diode and capacitor connected in parallel. Second transformer (T pace winding (n
s) (R4) and each transistor (Qs) (Q, 4
) tD x-E The diode (D4) is inserted between the
) is used to increase switching speed.

(n,) is the positive feedback winding of the first transformer (T1).

Its output is connected to the second transformer (T) via the resistor (R3).
is connected to the primary winding (R6) of the Here, the s2 transformer (TI) is a so-called saturation transformer that is used up to its saturation region. (ny) (ns) are the secondary windings of the first transformer (T1), and each transistor (Qs
MC4) (D collector potential (nl) (nx
) are provided correspondingly, and each output is connected to a resistor (R4).
After passing through a delay circuit including a capacitor (C,), a resistor (R5), and a capacitor (C6), and subjected to overlap prevention processing, the signals are output as signals a%b, c, and a.

These control signals a, b%c, d are applied to each pace and emitter of the switching transistors (Ql) (Qs) described above to control the oscillation of the inverter circuit (5). (7) is the positive feedback winding (
A rectifier circuit that rectifies the voltage induced in R6), (n・)
(n, ,) is the control winding of the second transformer (T) to which this rectifier output is input, and the resistor (R6) and transistors (Q, II) of the input control circuit (8) are in the middle. Connected.

(8) is an input control circuit that adjusts the input to the heated load, (9) is a rectifier circuit into which the detected current from the current transformer (CT) is input, (CT) is a smoothing capacitor, and Q□ is , a series circuit of a variable resistor (VR) and a resistor (R?) connected in parallel to this smoothing capacitor (C2),
A voltage signal VCT is obtained at both ends. This voltage vC! The value of can be arbitrarily changed by adjusting the variable resistor (VR). (ZD) (DI) is a Zener diode and a diode connected in series, (Q, l) is a diode (
The aforementioned transistor, to which the output of D6) is applied, the emitter-collector of which is connected to the positive feedback winding (ns) of the control circuit (6) and the control winding (R9), and whose impedance element Works as a. (Rs)
is a resistor connected between the collector and emitter of this transistor (Q,), which sets the oscillation frequency to approximately 40 KHz when the transistor (Q, 2, the oscillation frequency is approximately 2
It acts to set the frequency to 0KHz.

Next, the operation will be explained. When voltage VCC is applied to the control circuit (6), it is smoothed by a smoothing capacitor (Cm), and the voltage becomes a pulsating voltage vB that pulsates between about 100v and about 140v. Assuming that the transistor (C3) first becomes conductive due to this voltage vB, its collector
A current begins to flow between the emitters, and an induced voltage is generated in the positive feedback winding (nB) coupled to the collector winding (nl), and this induced voltage is transferred to the primary winding (R6) of the second transformer (Ts).
Further, an induced voltage is generated in the pace winding (ns) of the transistor (Qs) through the transistor (Qs). This voltage causes positive feedback in the transistor (C3) and complete conduction with sufficient pace current. The current flowing through the resistor (R3) increases linearly due to the primary inductance of the second transformer ('r, ) and reaches saturation.

As a result, the current on the primary side of the second transformer (Ts) increases suddenly, and the voltage drop across the resistor (Rs) increases, which causes the primary winding (nB) of the second transformer (T, ) to increase. The voltage across it decreases, and the feedback voltage decreases. Then, the voltage of the capacitor (C4) is applied to the pace of the transistor (Q, s) with the polarity shown in the figure, the transistor (C3) is cut off, and the transistor (C4
) starts energizing. Then, a feedback effect occurs in the opposite direction to the previous time, turning off the transistor (C3) and turning off the transistor (C3).
C4) is turned on. The primary current of the i@2 transformer (Tz) is reversed, and the transistor (C4) is turned on in the same way as when the transistor (C3) was turned on earlier.

Automatic oscillation continues in this manner. Primary transformer (
The two collector windings (n, ) (nl) of T1) are each electromagnetically coupled to the secondary winding (nγ) (ns), so depending on the on/off of the transistor (Cts) (Qs> , an output is obtained, and when the transistor (C3) is on, an on signal is obtained for the signal a%b, an off signal is obtained for the signal C1d, and on the other hand, when the transistor (C4) is on, the signal a
An off signal is obtained at %b, a signal c is obtained, and an on signal is obtained at (1).

When signals a, b and signals C, d are expressed in waveforms, they can be drawn as shown in FIG.

Next, the input control function will be explained. Input control is performed by increasing or decreasing the oscillation frequency. 1st transformer (TI)
When a magnetic bias is added to the second transformer (Tx) due to the voltage induced in the positive feedback winding (ns) of , the magnetic current increases and saturation is reached earlier. The oscillation frequency can be changed by changing the bias voltage.The bias voltage is changed by changing the impedance of the transistor (Qs).That is, the control winding (n・Mn1o)
The voltage appearing on the collector side of the transistor (C6)
It is the value obtained by subtracting the potential between the emitters, so by adjusting this potential, the potential applied to the control windings (ns) (nso) changes, and as a result, the magnetic current bias of the second transformer (T1) changes. The Rukoto.

The operation of the transistor (Q, i) is controlled by the input control circuit (8)
It is controlled by a variable resistance (V'R) within -. That is,
The input current detected by the current transformer (CT) is
The aftereffect is rectified in the rectifier circuit (9), and the smoothing capacitor (C
7), the voltage VCT is obtained between the variable resistor (VR) and the resistor (R7). Here, when it is desired to increase the input power, the voltage vCT is made small, and when it is desired to make the input power small, the voltage 'Vc'r is adjusted using a variable resistor (VR) so that it becomes large.

If the voltage ■CT is higher than the voltage between the Zener diode (ZD) and the diode (Ds), the transistor (Q
A voltage is supplied to the base of s) and acts in the direction of making it conductive. This increases the voltage applied to the control winding (n.) (nto), speeds up the magnetic saturation of the second transformer (T), and increases the oscillation frequency.

As the oscillation frequency increases, the input current decreases, so
The detection current of the current transformer (CT) also decreases, and the voltage v
cT decreases. In this way, the voltage VC? When becomes a value slightly larger than the voltage between the terminals of the Zener diode (ZD) and the diode (D,), a stable state is reached,
The input is a substantially constant value, that is, a value set by a variable resistor (VR).

Figure 3 shows the control winding (n・) of the second transformer (Ts).
(nso), primary winding (ns) and secondary winding (ns) (
The specific winding structure of n4) is shown, and the control winding (ns)
(n1o) is independently wound around two toroidal cores αη(2), and connected so that the current directions are opposite to each other.

The primary and secondary windings (no), (ni), and (n4) are wound around two core α forces (2) in the same direction. This can prevent AC voltage from being induced in the control winding (n@) (nto).

As described above, the induction heating cooker of the present invention uses a two-transformer self-excited oscillator as the control circuit of the inverter circuit, and has a configuration in which the oscillation frequency can be adjusted arbitrarily, thereby making it possible to use a conventional clock oscillator instead of the conventional clock oscillator. As a result, a new control circuit can be provided to replace the conventional control circuit, which eliminates the need for relatively large and expensive electrical components such as power transformers and pulse transformers. Furthermore, according to the present invention, the oscillation frequency of the automatic oscillator can be controlled by detecting the input current, converting it into voltage, and adjusting this value.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an operating waveform diagram, and FIG. 185 is a diagram of the winding configuration of the second transformer. (5)...Inverter, (6)...Control circuit, (8
)...Input control circuit.

Claims (1)

[Claims] 1. A series resonant circuit consisting of two unidirectional switching elements connected in series between the DC power supplies, a resonant capacitor and an induction heating coil connected in parallel to one of the switching elements, each connected in antiparallel to the above switching elements. In the induction heating cooker, the control circuit includes a diode, a control circuit that alternately operates the two switching elements, and an input control circuit that controls input to the negative shield.
A second transformer consisting of a first transformer and a positive feedback winding provided between the first and iI2 transformers, a control winding for controlling the magnetic saturation of the second transformer, and a secondary transformer of the first transformer. The input control circuit includes an impedance element that changes the magnetic saturation time of the control winding, and an impedance element that changes the magnetic saturation time of the control winding. The impedance element control circuit includes an impedance element control circuit that makes the impedance of the impedance element variable, and an input current detection circuit that detects the input current of the DC power supply, and the impedance element control circuit operates in response to the output of the input current detection circuit. A featured induction heating cooker.