JPH0715831B2 - Induction heating device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an induction heating device, and more particularly to an induction heating device having an improved power supply.

[Conventional technology]

FIG. 3 is a block diagram showing an example of a conventional induction heating device disclosed in, for example, Japanese Patent Publication No. 61-55234, and FIG. 4 is a signal waveform diagram of each part of the induction heating device shown in FIG. In the figure, (1) is a commercial power source, (2) is this commercial power source (1)
A fuse connected to one end of the commercial power supply and automatically shut off at the time of device failure, (3) a use selection switch connected to the other end of the commercial power source (1), and (4) a fuse selection (2) and a use selection switch ( 3) a first rectifier connected to, for example, a mixed bridge of thyristors and diodes,
(5) is a power supply circuit whose one end on the input side is connected to the output side of the fuse (2) and the other end is connected to the output side of the use selection switch (3). It supplies power for ICs and DC power for base drives. (6) is a first reactor for suppressing inrush current, which is connected to one end on the output side of the first rectifier (4), (7)
Has one end on the first reactor (6) and the other end on the first
The first smoothing capacitor (8) connected to the other end on the output side of the rectifier (4) is a first heating coil connected to one end of the first smoothing capacitor (7), and (9) is First
A first resonance capacitor (10) connected in parallel with the heating coil (8) of (1) is a first CT for detecting the zero point and the average value of the current flowing through the first heating coil (8). The first rectifier (4), the first reactor (6), the first smoothing capacitor (7), the first resonance capacitor (9), and the first CT (10) are used for the first rectification. A heating circuit is constructed. (11) is a switching transistor (11
a) and a protection diode (11b), the switching transistor (11a) has its collector terminal connected to the connection point (P) and its emitter terminal connected to the other end of the first smoothing capacitor (7). The protection diode (11b) has its cathode and anode connected to the collector terminal and the emitter terminal of the switching transistor (11a), respectively. (12) is an output control circuit which is connected to the first CT (10), has a comparator, and does not output the comparator output until it matches a preset target output, and (13) is the output control circuit ( 12), connected to the collector terminal and the emitter terminal of the switching transistor (11a), has a comparator, and outputs the comparator output when the correct collector-emitter voltage for the rating of the switching transistor (11a) is exceeded. The V _CE limiting circuit (14) is connected to the first CT (10) and forcibly resets (triggers) the sawtooth wave oscillation at the timing of the zero point of the output current of the first heating coil (8). Trigger circuit, (15) is an oscillator circuit connected to this trigger circuit (14) and constantly generates a sawtooth wave by resetting at the maximum period, and (16) is a signal for turning on the switching circuit (11). Is an on-pulse generation circuit that produces a signal, one input of which is connected to the oscillation circuit (15) and the other input of which is connected to the connection point (Q) via the resistor (16b) and the resistor (R) ( 16a), a resistor (16c) and a diode (16d) which are connected to the other input of the comparator (16a) and a connection point (T) of the resistor (16b) and are connected in series, and an input of the comparator (16a) It is composed of a resistor (16e) connecting the side and the output side and a resistor (16f) connected between the connection point (U) and the circuit power supply. Reference numeral (17) is a base drive circuit connected to the on-pulse generation circuit (16), which is connected to the base terminal of the switching transistor (11a) in the switching circuit (11). The power supply circuit (5), trigger circuit (14), oscillation circuit (15), on-pulse generation circuit (16), and base drive circuit (17) are connected to a common line (COM). (18) is connected to this common line (COM) and the output side is an on-pulse generation circuit (1
It is an interface circuit connected to the diode (16d) in 6) and includes a first photocoupler (18a) and a second photocoupler (30a). The device is remotely operated from the outside via the interface circuit (18). The soft start / limiter circuit (19) is connected to the common line (COM) and the input side is connected to the connection point (S), and this is a resistor (19) connected to the connection point (S).
a), a diode (19b) connected in series to this, a resistor (19c) connected between the circuit power supply and the connection point (V), one end connected to the connection point (V) and the other end grounded It includes an electrolytic capacitor (19d), a resistor (19e) connected between the connection point (W) and the circuit power supply, and a resistor (19f) having one end connected to the connection point (W) and the other end grounded. (20a) has a first operation switch whose one end is connected to the cathode of the diode in the first photocoupler (18a), and (21a) has one end connected to the collector terminal of the transistor in the second photocoupler (30a). The first display unit (22) is an external operating power supply, and its anode is the first photocoupler (18a).
Connected to the anode of the diode inside and the other end of the indicator (21a), and its cathode is connected to the other end of the first operation switch (20a) and the emitter terminal of the transistor in the second photocoupler (30a). Connected to. The oscillation control circuit includes the power supply circuit (5), the output control circuit (12), the V _CE limiting circuit (13), the trigger circuit (14),
It includes an oscillator circuit (15), an on-pulse generation circuit (16), a base drive circuit (17) and a soft start / limiter circuit (19). The high frequency power source is the commercial power source (1), fuse (2), use selection switch (3), first heating coil (8), first operation switch (20a), first display of the above components. Device (21a) and external operation power supply (22)
It is composed by excluding.

The conventional induction heating device is configured as described above, and its operation will be described below. FIG. 4 shows the waveforms of the signals (a) to (f) such as voltage at the main points (a) to (f) in FIG. 3. First, the external first operation switch (20a) When it is open, the potential of the part indicated by zone (a) in Fig. 4 (c) is on the positive side, so the control signal voltage is clamped to zero volt through the diode (16d) built in the on-pulse generation circuit (16). Has been done. Therefore, the output that is the result of comparison with the sawtooth wave signal given to the other terminal of the comparator (16a) of the on-pulse generation circuit (16) is at "L" level. Therefore, the oscillation operation is not performed, and the oscillation wait state is set.

Next, after closing the first operation switch (20a) for a while, the zone (b) in Fig. 4 shows the period for a while, and the zero volt clamp of the control signal voltage is released because the potential of (C) drops, so the soft The control signal voltage gradually rises as shown in FIG. 4 (b) due to the CR time constant of the capacitor and resistor in the start / limiter circuit (19). Then, when the on-pulse generation circuit (16) outputs an on-pulse having a waveform as shown in FIG. 4 (d) at the crossing point with the sawtooth wave, the base drive circuit (17) operates and the switching circuit (11).
Since the switching transistor (11a) is turned on and off, as shown in FIG. 4 (e), the first heating coil (8)
It oscillates with the coil current flowing through the coil and the coil voltage applied to the first heating coil (8). Once oscillated and the coil current flows, the first CT (10) detects the coil current, so the trigger circuit (14) operates and the sawtooth wave is forcibly reset. Therefore, when the width of the on-pulse is narrow, the coil current is small and the current zero point is reached in a short time, so that the trigger circuit (14) interrupts and resets the sawtooth wave so that the oscillation frequency is high.

Next, the stable state after the CR time constant of the soft start / limiter circuit (19) has elapsed is shown in the zone (c) of Fig. 4,
The output comparator of the output control circuit (12) is properly turned ON-OF.
Since the control signal voltage is controlled to be almost constant by repeating F, the on-pulse generation circuit (16) outputs a pulse of a constant width as shown in FIG. 4 (d), and thus FIG. 4 (e).
The coil voltage and current are maintained at desired constant values as indicated by. When the load supported by the first heating coil (8) suddenly decreases, the coil voltage rises rapidly, so that the voltage between the collector terminal and the emitter terminal of the switching transistor (11a) also rises, and V _CE Limiting circuit (13)
The comparator of turns on and works to lower the control signal voltage (b). This protects the switching transistor (11a) from being damaged by an overvoltage caused by a sudden change in load. FIG. 4 (f) shows how the output of the induction heating device changes with time after the first operation switch (20a) is closed and the induction heating device starts operating.

[Problems to be solved by the invention]

In the conventional induction heating device as described above, a plurality of high-frequency power supplies are required in an application in which a plurality of first heating coils (8) are required, which causes problems such as increase in equipment cost and space. I got it.

The present invention has been made in order to solve such a problem, and an object thereof is to obtain an induction heating device capable of reducing equipment cost and space even in an application using a plurality of heating coils.

[Means for solving problems]

The induction heating device according to the present invention includes a plurality of heating coils that supply thermal energy to an external load, and a plurality of heating coils that are provided corresponding to each of the heating coils and that are connected in parallel with each other and that each include a controllable rectifier and a commercial power A plurality of rectification heating circuits that rectify and generate the thermal energy in the heating coil, a switching circuit that is connected to these rectification heating circuits and turns ON / OFF the oscillation of the heating coil, and is connected to the switching circuit and the rectification heating circuit. Is
The oscillation is caused by the magnitude of the current flowing through the heating coil.
An oscillation control circuit that is turned on / off and accordingly turns on / off the switching circuit, and means for controlling application of a rectification / smoothing voltage to the heating coil and the switching circuit by controlling the rectifier are provided. It is a thing.

[Action]

In the present invention, a plurality of rectification heating circuits can be turned ON / OFF, and the outputs of the heating coils provided corresponding to these can be independently controlled.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the induction heating device of the present invention, and FIG. 2 is a signal waveform diagram of each part of FIG.
(1)-(11), (11a), (11b), (13), (15)-
Since (17), (19), (20a), and (21a) are exactly the same as the conventional example, the description is omitted. In this embodiment, the rectification heating means in which the first rectification heating circuit of the conventional example and the second rectification heating circuit having exactly the same configuration as this are connected in parallel has one end and the other end on the output side. Are connected to the collector terminal and the emitter terminal of the switching transistor (11a) in the switching circuit (11), respectively. In detail,
(4a) is a second rectifier connected to the other end of the fuse (2) and the other end of the use selection switch (3), and (6a) is connected to one output terminal of the second rectifier (4a). Second
, (7a) is a second smoothing capacitor whose one end is connected to this second reactor (6a) and the other end is connected to the other output terminal of the second rectifier (4a), and (8a) is a second smoothing capacitor. Second heating coil connected to the reactor (6a) of (9
a) is a second resonance capacitor connected in parallel with this second heating coil (8a), and (10a) is the second heating coil (8a).
It is the second CT that is connected to a) and detects the current flowing through it. One end thus connected in parallel serves as a connection point (P) and is connected to the collector terminal of the switching transistor (11a) in the switching circuit (11). (12A) is connected to the first CT (10) and the second CT (10a) and has, for example, an OR circuit, and the output control circuit (14A) used in the present invention is the first CT (10A). ) And a second CT (10a), for example a trigger circuit having an OR circuit, (18A)
Is the interface circuit used in this invention,
A third photo coupler (18b) and a fourth photo coupler (30b) are newly added. (20b) is a second operation switch used in the present invention, one end of which is connected to one end of the first operation switch (20a) and the negative side of the external operation power source (22), and the other end of which is the third operation switch. Photo coupler (18
It is connected to the diode in b). (21b) is a second indicator used in the present invention, one end of which is connected to one end of the first indicator (21a) and the positive electrode side of the external operating power source (22), and the other end of which is the fourth indicator. It is connected to the collector terminal of the transistor in the photo coupler (30b).

The induction heating device configured as described above operates as follows. First operation switch (20
a) When the second operation switch (20b) is OFF, the interface circuit (18A) does not output the ON signal to the controllable first rectifier (4) and second rectifier (4a). , The first reactor (6), the first smoothing capacitor (7), the second reactor (6a), the second smoothing capacitor (7a) rectified voltage output to the DC smoothing section is not output .

On the other hand, since the zero-pulse clamp level signal is also sent to the on-pulse generation circuit (16), the output control circuit (12
The control signal voltage applied to the line connecting A), the V _CE limit circuit (13) and the soft start / limiter circuit (19) is still zero volt, so the on-pulse with the sawtooth wave generated in the oscillator circuit (15) Since the output of the comparator of the generation circuit (16) as a comparison result is always "L", the base drive signal is not output. Therefore, since there is no voltage in the first heating coil (8) and the second heating coil (8a) and the switching transistor (11a) does not turn on, the oscillation is stopped in this state and the first operation switch is turned on. (20a) and the second operation switch (20b) are in the standby mode. At this time, as shown in FIG. 2, the cathode voltages (C ₁ ) of the first and third photocouplers (18a) and (18b),
Both (C ₂ ) are at “H” level.

Next, when the first operation switch (20a) is turned on, the cathode voltage (C ₁ ) of the first photocoupler (18a) becomes low level, and the interface circuit (18A) moves to the first rectifier (4). Since an ON signal is output, a current flows through the first reactor (6) and the first smoothing capacitor (7), the output (f ₁ ) of the first rectifier (4) rises, and the smoothed voltage becomes the first It is added to the series portion of the heating coil (8) and the switching transistor (11a). Interface circuit (18
Since the signal voltage from A) to the on-pulse generation circuit (16) is released from zero volt, the output control circuit (12A), V _CE
The control signal voltage applied to the line connecting the limiting circuit (13) and the soft start / limiter circuit (19) rises according to the CR time constant of the soft start / limiter circuit (19). Then, while the control signal voltage is higher than the lower peak value of the sawtooth wave coming from the oscillation circuit (15), the on-pulse generation circuit (16) outputs “H” level, so that the base drive circuit (17) A switching transistor (11
Pace drive so that a) is turned on and turned off during the “L” level period. As a result, a current flows through the first heating coil (8) and the switching transistor (11a), and then is cut off.
Vibration is generated at a frequency determined by the inductance of the heating coil (8) and the capacitance of the first resonance capacitor (9), and the coil voltage and coil current also change according to the vibration. At this time, the first CT (10) gives a voltage signal corresponding to the coil power supply to the output control circuit (12A) and the trigger circuit (14A) by the added resistance. Then, the interface circuit (18A) drives the first display (21a). The output control circuit (12A) averages this coil current signal,
When the average value exceeds the output setting reference as compared with the preset output setting reference, the comparator output of the output control circuit (12A) operates so as to become the “L” level. Also, the trigger circuit (14A) catches the zero point of the coil current signal and resets (triggers) the oscillator circuit (15) at that timing.
To act like. Therefore, the ON pulse width, coil current, and coil voltage increase in accordance with the gradually increasing control signal voltage, and the output of the comparator of the output control circuit (12A) repeats the "L" level and "H" level properly. Stable oscillation continues with the control signal voltage kept almost constant. In this state, the second operation switch (20
When b) is turned on, the cathode voltage (C ₂ ) of the third photo coupler (18b) becomes “L” level, and the interface circuit (18A) stops the ON signal of the first rectifier (4) for a predetermined time. , The zero volt clamp signal to the on-pulse generation circuit (16) is output, so the first rectifier (4) is turned off,
Since the switching transistor (11a) will not turn on, oscillation will stop. However, when a predetermined time passes, an ON signal is output to each of the first rectifier (4) and the second rectifier (4a) [the respective outputs (f ₁ ) and (f ₂ ) rise],
Since the zero volt clamp signal to the on-pulse generation circuit (16) is released, this time the parallel circuit formed by the first heating coil (8) and the second heating coil (8a) and the switching transistor (11a) are connected. An electric current flows through the configured series circuit, and the oscillation operation is performed in the same manner as when the first operation switch (20a) is turned on by itself, and the interface circuit (18A) causes the first and second display devices (21a) to operate. ), (21b) are driven. At this time, the first CT (10) and the second CT (10
The coil current signal from a) is given to the output control circuit (12A) and the trigger circuit (14A). Since both circuits have the function of selecting and using the one with the largest value of the two coil current signals, O of switching transistor (11a)
The timing of N and OFF does not go wrong.

Although the commercial power source (1) has a single phase in the above embodiment, it may have three phases. In addition, the oscillation control circuit does not use the trigger circuit (14A) and the oscillation circuit (15), and the first CT (1
0), the current waveform of the second CT (10a) may be changed to a sawtooth wave, and the on-pulse generating circuit (16) may be provided with a circuit configuration to improve the accuracy of current control.

[Effects of the Invention] As described above, the present invention includes a plurality of heating coils that supply heat energy to an external load, and a rectifier that is provided corresponding to each of the heating coils and that is connected in parallel with each other and that is controllable. A plurality of rectification heating circuits for rectifying a commercial power source and generating the thermal energy in the heating coil, a switching circuit connected to these rectification heating circuits to turn on / off the oscillation of the heating coil, the switching circuit and the rectification Connected to the heating circuit,
The oscillation is caused by the magnitude of the current flowing through the heating coil.
An oscillation control circuit which is turned on / off and accordingly turns on / off the switching circuit, and means for controlling application of a rectification / smoothing voltage to the heating coil and the switching circuit by controlling the rectifier are provided. Therefore, the device can be manufactured at low cost, the required space is small, and more detailed output control can be performed.

[Brief description of drawings]

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part of FIG. 1, FIG. 3 is a block diagram showing a conventional induction heating device, and FIG. 4 is FIG. 3 is a signal waveform diagram of each part of FIG. In the figure, (1) is a commercial power source, (4) is a first rectifier, (4a) is a second rectifier, (5) is a power supply circuit, and (6).
Is the first reactor, (6a) is the second reactor,
(7) is the first smoothing capacitor, (7a) is the second smoothing capacitor, (8) is the first heating coil, (8a) is the second heating coil, (9) is the first resonance capacitor, (9a) is the second resonance capacitor, (10) is the first CT, (10a) is the second CT, (12A) is the output control circuit, (13) is the V _CE limiting circuit, and (14A) is the trigger. Circuit, (15) oscillator circuit, (16)
Is an on-pulse oscillator circuit, (17) is a base drive circuit,
(18A) is an interface circuit, and (19) is a soft start / limiter circuit. In each drawing, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A plurality of heating coils for supplying heat energy to an external load, corresponding to each of these heating coils and connected in parallel with each other, each including a controllable rectifier,
A plurality of rectification heating circuits for rectifying a commercial power source and for generating the thermal energy in the heating coil, a switching circuit connected to these rectification heating circuits to turn ON / OFF the oscillation of the heating coil, the switching circuit and the rectification heating An oscillation control circuit that is connected to a circuit and that turns on / off the oscillation according to the magnitude of the current flowing through the heating coil and turns on / off the switching circuit accordingly; and the heating coil by controlling the rectifier. An induction heating apparatus comprising means for controlling application of rectification / smoothing voltage to the switching circuit. 2. The induction according to claim 1, wherein the number of heating coils is two, the rectification heating circuit includes first and second rectifiers, and each rectifier is a mixed bridge of thyristors and diodes. Heating device. 3. The induction heating device according to claim 1, wherein the switching circuit is turned off when either one of the peak values of the current flowing through each heating coil matches a preset predetermined value.