JPH02148686A - Electromagnetic cooker - Google Patents

Abstract

PURPOSE:To reduce the power consumption under a standby condition and improve the reliability of a drive means or the like by separating an output element from the control with the drive means and connecting the input terminal of the output element to the ground when the standby condition is detected. CONSTITUTION:There are provided means 6 for detecting a standby condition in which induction heating is stopped, means 10 for separating an output element Q1 from the control with a drive means 9 when the standby condition is detected, and means 11 for connecting the input terminals of the output element Q1 to the ground of the positive and negative power sources. This turns the output element Q1 off surely under the standby condition and reduces the power consumption of the negative power source required for turning the output element Q1 off.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B1 Overview of the invention C0 Prior art ■]6 Problem to be solved by the invention E1 Means for solving the problem 1.1 Effect G. Example C7. Example (1) +M formation (Fig. 1, m2) Gy,
Effects of Examples ++, Effects of the Invention Δ, Industrial Application Fields The present invention improves reliability by lowering power consumption and reducing heat generation of circuit components in standby mode ■ when induction heating is stopped. This relates to an electromagnetic cooker.

B0 Summary of the Invention The present invention provides an electromagnetic cooker that performs induction heating by passing a high frequency current through a work coil using an output element driven using a positive power source and a negative power source. The output element is separated from the control of the drive means, and the input terminal of the output element is connected to the ground of the positive power supply and the negative power supply to ensure that the output element is turned off. By reducing the current flowing through the negative power supply without reducing its heat generation, we have reduced power consumption during standby mode and improved the reliability of the drive means, etc.

C1 Conventional technology Conventionally, an output element controlled by a drive circuit sends a high current of 12 kri through a work coil, and when the magnetic field lines generated at that time pass through a metal container, they generate eddy currents in the container and generate heat. An electromagnetic cooker that performs induction heating by
No. 2, JP-A No. 63-58787, etc.). Above m magnetic cooking 4
Transistors, GTOs (gate turn-off thyristors), and the like are mainly used as output elements.

The output element is turned on and off at high frequency under the control of the drive circuit described above, and at this time, a negative power supply is used to set the human power potential (base potential) of the transistor, etc. when it is off to a negative potential, and the switching characteristics (switching speed, etc.) when it is off are changed. ).

D0 Problems to be Solved by the Invention However, in the m[,'J physical equipment in the above-mentioned conventional technology, when there is no container etc. placed on it or when the container is removed after completion of heating, the control of the drive circuit is difficult. When the output element is turned off by stopping the output element, the base potential of the output element is kept at a negative potential, so current continues to flow through the drive circuit, causing heat generation in the drive element, etc.
Problems such as an increase in drive power and an increase in the power supply circuit have been caused by tn<. Heat generated by drive elements leads to a decrease in reliability, an increase in drive power leads to an increase in wasteful power consumption, and an increase in the number of power supply circuits, along with the problem of heat generation, eliminates the need for cooling means such as fans. This also becomes an obstacle to cost reduction and miniaturization.

The present invention was devised to solve the above problems, and as a result, it suppresses the heat generation of the drive means of the output element when the induction heating is stopped and is in a standby state, thereby reducing power consumption and improving reliability. The purpose of the present invention is to provide a porcelain cooker with improved characteristics.

21 Means for Solving the Problems In order to achieve the above object, the configuration of the magnetic cooker of the present invention is such that an output element controlled by a drive means using a positive power source and a negative power source applies a high frequency current to a work coil. In an electromagnetic cooker that performs induction heating by flowing current, means for detecting a standby state in which induction heating is stopped; means for separating the output element from control by the drive means when the standby state is detected; The apparatus is characterized by comprising means for connecting the input terminal of the output element to the ground of the positive power supply and the negative power supply when a standby state is detected.

F1 action The present invention detects the standby state in which induction heating is stopped, disconnects the output element from the control of the drive means by means of separation, connects the input terminal of the output terminal to the ground of the power supply, and returns to the standby state. To turn off an output element reliably and eliminate current consumption of a negative power supply conventionally required by a drive means to turn off an output element.

G. EXAMPLES Hereinafter, examples of the present invention will be described in detail based on the drawings.

Configuration of G1 Embodiment (FIGS. 1 and 2) FIG. 1 is a block diagram of an electromagnetic cooker showing an embodiment of the present invention. Ll is a work coil, and magnetic lines of force generated by a high-frequency current flowing through the work coil cause eddy currents to be generated in a metal container such as a pot 2 placed on a top plate 1 made of glass ceramics or the like, thereby inductively heating it. 3 indicates a commercial AC power supply, which is connected to the input end of a rectifier circuit 4 using a diode bridge via a relay RYt. The positive output side of this rectifier circuit 4 is connected to one end of the work coil L1 via a choke coil L, and the negative output side is connected to the ground GND of the circuit via a resistor R6 for load detection. Capacitors Co and C3 are connected between both ends of the choke coil LI and the ground GND, and these capacitors Co
, C1 and choke coil L.

constitutes a smoothing circuit of the rectifier circuit 4. C2 is a resonance capacitor connected in parallel to the work coil L1. The other end of the work coil L is connected to the ground GND via an output transistor Q1 which is an output element, and a damper diode D is connected in parallel to this transistor Q1. The above constitutes an output circuit for induction heating, and this output circuit supplies a sawtooth wave-like high frequency current to the work coil L by controlling the output transistor Q1 on and off, thereby performing induction heating of the pot 2 and the like. In this case, if the period of the sawtooth waveform is increased, that is, if the on/off frequency of transistor Q1 is decreased, the work coil L
, the average current flowing through the circuit increases and the output can be increased.

The circuit configuration of this embodiment for controlling the on/off of the output transistor Q will be described below. 5 connects the commercial AC power supply 3 to the input terminal, and stabilizes the positive voltage Hr -+-o, negative power supply -Vcc and positive power supply element B necessary for each circuit.
This is a power supply circuit that supplies ss.

S is a push button type main switch, and when it is turned on, the relay RYI is operated by the power source of the power supply circuit 5, and the commercial AC power source 3 is turned on to the induction heating output circuit. Thereafter, relay RY is held by a load detection output, which will be described later. 6 is a power supply detection circuit which is a standby state detection circuit;
Since there is no drop in the positive power supply element B and the main switch S1 is turned on and the load is detected, the normality of the power supply is detected, and a command is given to the oscillation control circuit 7 to start oscillation. If the normality of the power supply is not detected in the above, that is, if it is detected that the positive power supply element B is abnormally low or that the load is not detected, a command to stop oscillation is given. This state is a standby state in which induction heating is not performed. Note that the start/stop of oscillation of the oscillation control circuit is also commanded from the load detection circuit described later. 8 is an oscillation circuit (OSC) for a rectangular wave signal of 20 KHz to 30 KHz whose start/stop of oscillation is controlled by the oscillation control circuit 7, and 9 is a drive that controls on/off the output transistor Q1 based on the rectangular wave signal. It is a circuit. The drive circuit 9 is electrically connected to or separated from the base of the output transistor Q1 by a first switch circuit 10, and the base of the output transistor Q is electrically connected to or separated from the ground GND of the power supply circuit 5. 2
Switch circuit! Connected to 1. I2 top play due to voltage drop of resistor R0 due to load current of output circuit)
A load detection circuit detects that gJ%6 etc. is placed on i, 13 is a volume vR that controls the oscillation frequency of the oscillation circuit 8.
This is an output control circuit that controls the oscillation frequency by comparing the setting of 1 with the load current detected by the resistor R6 using a comparator, thereby making it possible to increase the output of the output circuit. The load detection signal of the negative 6jj detection circuit 12 is a signal that is output when the load current detected by the resistor R is equal to or higher than the reference potential by comparing it with the base *i position. etc. and holds the relay rt y . Also, if no load is detected and the load detection signal is cut off, the relay FL Y is restored and the 1X of the power detection circuit 6 is turned off.
In addition to cutting off the normality detection signal of the source and making it a standby state detection output, the control circuit 7 is commanded to stop oscillation. The time constant circuit 14 is a circuit that delays and outputs a signal that connects the first switch circuit 10 and the second switch circuit 11, respectively, and the signal is a standby state detection output (normal A signal with the opposite logic to the detection signal) is generated by delaying it by a time constant of a predetermined time. For the above-mentioned predetermined time, after the oscillation circuit 8 stops oscillating and the drive circuit 9 is in a stable state, the first switch circuit 10 is placed in a disconnected state and the second switch circuit 11 is connected to the ground. This is the delay time required for The constant voltage +Vss of the power supply circuit 5 is especially the above-mentioned time constant circuit! 4 is made accurate, and the base QTi of the load detection circuit 12 is
This is necessary for accurate positioning and accurate load sensing.

FIG. 2 is a circuit configuration diagram showing a specific circuit example of the main part of the above embodiment. In Figure 2, blocks indicated by dotted lines indicate specific circuits, and each block or member corresponding to Figure 1, including other blocks, is given the same reference numeral as in Figure 1. There is. ? The Tm source circuit 5 is a transformer T
1, a rectifier circuit 51, and a transistor Q7. Zener diode Dt.

and a constant voltage power supply circuit consisting of a resistor 111n. The transformer T1 has at least two outputs on the secondary side, one of which is rectified by a rectifier circuit 51 to provide a negative power supply -Vcc,
The other side is a positive power supply element B, and the ground side of each power supply is commonly connected to the ground GND of the circuit. Transistor Q2
The collector of is connected to the positive power supply element B, a resistor R1 is connected between the base and the collector, a Zener diode Dt and a resistor R6 are connected in series between the base and ground GND, and a constant voltage is applied from the emitter of the transistor D. +Vss is output.

The voltage detection circuit 6 includes transistors Q, Q, connected in series, each having its emitter connected to the ground.

It consists of circuits Q,,Q,. The base of the transistor Q is connected to the other end of a push-button main switch S1, which has one end connected to the positive power source B through a resistor R1. The other end of this main switch S1 is connected to a load detection signal of a negative 6 (j) detection circuit I2, which will be described later, and is also connected to a relay R, which will be described later.
It is connected to the input side of the drive circuit 15 of Y. The collector of transistor Q is pulled up to the positive power supply element B by resistor R4, and is directly connected to the base of transistor Q4, and the collector of transistor Q is connected to Zener diode D of the constant voltage power supply circuit of power supply circuit 5 and resistor R2. When connected to the connection point, it is directly connected to the base of transistor Q6. The collector of the transistor Q is pulled up to the positive power supply B by the resistor rls, and the collector of the transistor Q6
Connect to the base of the circuit and the time constant circuit (4) described later. Transistor Q. The collector of is kept at constant voltage +V by resistor R.
Pulled up to SS and input to control circuit 7.

According to +1 above, in the steady state, when the main switch S is pressed and the load detection signal is sent out, the transistor Q is turned on, the transistor Q4 is kept off, and if the positive power supply element B is normal. Since the potential of the resistor R2 is about to become higher than the base potential of the transistor Q5, the transistor Q6 is turned on and the transistor Q is turned off, and a normal detection output (high level) is sent to the oscillation control circuit 7.
is input as an oscillation command. In the above, when the positive power supply element B drops abnormally due to a drop in input voltage, etc., the potential of the resistor R2 becomes lower than the base potential of the transistor Q, turning off the transistor Q, turning on the transistor Q0, and turning on the transistor Q. The output of , becomes low level, instructing to stop oscillation. Also, the pot 2 etc. is on the top plate l.
When the load detection signal of the load detection circuit 13 is cut off, the transistor Q is turned off and the transistor Q4 is turned on. The time constant circuit 14 operates when the transistor Q is turned from on to off.

Is the drive circuit 9 negative for each emitter? ! ! Source Vc
The circuit consists of two stages of directly connected transistors Q7, Q, and L, and normally a rectangular wave signal from an oscillation circuit 8 is input to the base of transistor Q, and transistor Q8 controls the on/off of output transistor Q. The base of the transistor Q is also connected to a first switch circuit IO, which will be described later, and can be fixed in the on state by its output current. The collector of the transistor Q7 is connected to the ground CHD through a resistor R7, and the collector of the transistor Q7 is connected to the ground CHD through a resistor R7.

directly connected to the base of The collector of transistor Q is
The coils are connected in series and connected to the ground GND via a cement resistor R8. The on/off control of the transistor Q1 is such that the energy stored in the coil L when the transistor Q is off is transferred to the transistor Q6.
This is done by discharging the current as the base current of the output transistor Q1 when the cycle is on, and controlling the transistor Q to turn on. The transistor Q1 is generally of Darlington type, and its base is brought to a negative potential -Vcc by turning on the transistor Q in order to improve the operating speed when the transistor Q1 is turned off. Negative power supply -Vcc
and ground GND, a capacitor C1 is connected for smoothing.
Connect.

The first switch circuit IO is composed of a transistor Q, the collector of which is connected to the base of the transistor Q7 of the drive circuit 9 through a reverse current blocking diode D. The emitter of transistor Q is resistor R,
It is connected to the output side of a time constant circuit 14, which will be described later, through the circuit, and its base is connected to the ground GND. When the transistor Q receives the output from the time constant circuit I4, it turns on and keeps the transistor Q on and the transistor Q off.
The transistor Q1 of the drive circuit 9 is placed in a separated state in which on/off control is not performed. The second switch circuit +1 is a transistor Q whose emitter is grounded to the ground GND. This circuit connects the base of the output transistor Q to the ground GND in order to ensure that the output transistor Q1 is turned off when the drive circuit 9 is in the separated state. The base of the transistor Q1° is connected to the output side of the time constant circuit 14 via a resistor R9° and to the ground GND via a resistor R11. The collector of transistor QIo is transistor Q. It is connected to the base of the transistor Q through a diode D4 to prevent current from flowing from the side to the transistor Q1.

The time constant circuit 14 includes a switch element S that is turned on by a high-level control input, and a time constant circuit that includes a resistor R11, a capacitor C4, and a diode D. Resistance R
1, one end is connected to the voltage regulator Vss, the other end is connected to the ground GND via the capacitor C4,
It is connected to the anode side of the diode Ds and the control input terminal of the switch element S. The cathode side of the diode D is connected to the collector of the transistor Q of the power supply detection circuit 6.

The input terminal of the switch element S is connected to the voltage regulator Vss,
On the output side, as described above, the first switch circuit lO and the second switch circuit 1! Connect to.

In the normal state where induction heating is performed, the transistor Q6 is on, the capacitor C4 is discharged through the diode D, the control input of the switch element St is kept at a low level, and the switch element S is turned on. The first switch circuit 10 is turned off, and the second switch circuit is turned off. Next, when the standby state is detected, the transistor Q5 is turned off, and the capacitor C
6 is charged by the resistor R1, and after a predetermined period of time becomes 1 level, turning on the switch element S, and turning on the first switch circuit and the second switch circuit.

Relay drive circuit! 5 is a switch circuit including a transistor QIr whose emitter is grounded to the ground GND. The base of the transistor Q11 is connected to the resistor R,,,r
The other end of the resistor R13 is connected to the positive atom B via the push button main switch S, and the resistor R13 is connected to one end of the resistor R13.
The other end of l14 is connected to ground GND. Also, the other end of resistor R13 is the load detection circuit! Connect to the output side of the load detection signal of No.2. The collector of transistor Q is connected to one end of the coil of relay RYl, the other end of the coil of relay RY is connected to positive atom B, and its contact is inserted and connected between commercial AC power supply 3 and rectifier circuit 4. In the above configuration,
When main switch S1 is pressed, transistor Q is activated.

, is turned on, relay It Y operates, and the commercial AC 71i 3 is input to the output circuit. Here, if the pot 2 or the like is placed on the top plate l, the load detection circuit I2 detects the load, and the transistors Q and 1 continue to maintain the on state based on the load detection signal. In the above, when the pot 2, etc. is removed from the top plate 1, the load detection signal is cut off, the transistor Q+t is turned off, and the relay RY is restored and enters a standby state in which heating is stopped.

The configuration of other blocks is as explained in FIG.

G2. Effect of the embodiment The operation of the embodiment configured as above will be described.

First, in the standby state where main switch Sl is not pressed and heating is stopped, load detection is not performed, and transistor Q
, off, transistor Q4 turns on, transistor Q6 turns off, and switch element S! is turned on, and the transistor Q of the first switch circuit 10 and the transistor Q1° of the second switch circuit 11 are kept on. As a result, the base of the transistor Ql is electrically disconnected from the drive circuit 9, and the base of the transistor Q1 is connected to the ground GND.
is kept off. At this time, transistor Q.

is off, so in the drive circuit 9, the resistors R,
Coil 3. Through the transistor Q, the negative power supply -Vcc
The current of around 500 to 600 mA that flows through the circuit disappears.

Next, when the main switch S1 is pressed and turned on, the relay flY is turned on and the commercial AC iX source 3 is supplied to the output circuit of the work coil L. When the main switch S1 is pressed, as described above, the transistor Q4 is turned off, the transistor Q is turned on, the switch element St is turned off (open), and the transistors Q, , Q, are turned off. Therefore, the drive circuit 9 is connected to the transistor Q1.
It is electrically connected to the base and can be controlled on and off. At this time, when the load detection circuit 12 instructs the oscillation control circuit 7 to start oscillation, the oscillation control circuit 7 causes the oscillation circuit 8 to output a rectangular wave signal, and the output transistor Q is controlled on/off by the drive circuit 9. Heating begins and it begins to function as an electromagnetic cooker.

In the above normal state, if the power supply voltage drops or the load (pot 2) is removed, the transistor Q
, is turned off, transistor Q, is turned on, and a command is given to stop oscillation. Note that the load detection circuit 12 also issues a command to stop oscillation at the same time. When the oscillation circuit 8 stops oscillating in this way, the heating stops. In this state, the base of the transistor Q is kept at a negative potential (-Vcc) since the transistor Q7 is turned off, and the transistor Q is turned on, and at this time, the base of the transistor Q is maintained at a negative potential (-Vcc). A current flows through the transistor Q0 to the negative power supply -Vcc. However, when transistor Q is turned off and its output becomes high level, switching element S is turned on with a time constant determined by resistor R1 and capacitor C4, and transistor Q
,,Q,. are both turned on, and the transistor Q of the drive circuit 9 is turned on.

is turned on, transistor Q is turned off, the base of output transistor Q is separated from drive circuit 9, and its base potential is maintained at ground GND, and output transistor Q is reliably turned off and placed in a standby state. .

Even in this standby state, since the transistor Q is off as described above, the resistor Rs and the coil 3. Transistor Q.

Several hundred mA of current flowing through the negative 7[ to source -Vcc is eliminated. Further, since no current flows from the base of the output transistor Q to the transistor Q, the power consumption of the entire drive circuit 9 in the standby state is significantly reduced. In the standby state, the heat generation of the resistor R and the coil 3. The heat generated by the transistor Q is eliminated, and the heat generated by the transistor, etc. is also reduced. Therefore, the reliability of those parts can be improved. Further, the ratings of these elements can be reduced, the mounting space on a board etc. can be reduced, and the need for cooling fans etc. can be eliminated.

In the embodiment shown in FIG. 2, the oscillation circuit 8 is set to the oscillation stopped state and the transistors Q, ,Q,. Table 1 shows an example in which the drive current flowing to the negative power supply -Vcc of the drive circuit 9 was measured when the power supply was turned on and off.

Transistor Q,,Q,. The state where is turned off corresponds to the drive current in the standby state in the conventional example. As is clear from Table 1, the drive current is approximately 1/1 of the conventional one.
It can be set to 0 or less.

Table 1 Q,,Q,. The drive current that flows when turned on is mainly caused by the resistance R.
This is the current flowing through 3.

It should be noted that the above-mentioned embodiment is merely an example, and the present invention can be applied to various output elements and their drive circuits. The switch circuit and the second switch circuit section can also be modified as appropriate to suit their output elements and drive circuits. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with its gist.

1-1. Effects of the Invention As is clear from the above explanation, the electromagnetic cooker of the present invention provides the following effects.

(1) Power consumption in the standby state when the output element is turned off can be reduced, heat generation of parts can also be reduced, and reliability can be improved.

(2) Since the drive power of the output element is reduced, the cost of power supply circuit components can be reduced, and the efficiency of the entire device can be increased.

(3) Since the ratings of drive circuit components and power supply circuit components can be reduced, the board area and mounting space can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific circuit example of the main part of the above embodiment. 5...7t J circuit, 6...power supply detection circuit, 8...
- Oscillation circuit, 9... Drive circuit, IO... First switch circuit, 11... Second switch circuit, 12.
...Load detection circuit, 14...Time constant circuit, Ql...
Output transistor, L...work coil.

Claims (1)

[Claims] (1) In an electromagnetic cooker in which an output element controlled by a drive means using a positive power source and a negative power source causes a high-frequency current to flow through a work coil to perform induction heating, means for detecting a standby state in which the induction heating is stopped; , a means for separating the output element from the control by the drive means when the standby state is detected, and connecting the input terminal of the output element to the ground of the positive power supply and the negative power supply when the standby state is also detected. An electromagnetic cooker comprising a means for: