JPS61237391A - Induction heater - 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 A) Field of Industrial Application The present invention relates to an induction heating device (:), and particularly (: its output control).

[Existing technology] The conventional induction heating device consists of a full-wave rectifier circuit that full-wave rectifies an AC power source, a coupled induction heating coil, and a resonant capacitor that forms a resonant circuit together with the induction heating coil. and a switching element which is connected to the resonant circuit and generates a resonant current in the resonant circuit, and by controlling the switching element ON and OFF, the resonant circuit (which generates an oscillating current) is connected. Induction heating coil (: A device that inductively heats objects placed in close proximity.

By the way, such an induction heating device, Tokko 2, household induction heating device, for example, is disclosed in Japanese Patent Publication No. 59-47877 4;
The ON/OFF states of the switching elements are controlled so that the AC input current is equal to a predetermined set level. This control method # Since the input voltage of the rectifying AC power source is constant, the AC input current is proportional to the AC input power, and this AC input power is approximately proportional to the absorbed power of the object to be heated, that is, the heating energy. By using this method, relatively easy heating control can be obtained.

c) Problems to be solved by the invention However, even in such an induction heating device f11,
When heating an object at the same setting level, the input power input by two people will differ slightly depending on the material of the object (and the actual power inside the device). For example, an enameled pot (enamel/iron/enamel) will vary from 1 to 100W. When heating 6-layer stainless steel M (18-8 stainless steel/iron/18-8 stainless steel) at a general constant level where an input of 1675 to 140 Qw is input, a phenomenon occurs. The increase in input power becomes stronger as the material of the object to be heated becomes weakly magnetic.

The cause of this is not well understood at present, but if the material of the heated object is weakly magnetic than ferromagnetic, the frequency will be higher (:), and - times of oscillation (:
less energy is supplied.

For this reason, the amplitude of the noise component superimposed on the AC input current (:) is also higher for a ferromagnetic heated object, and lower for a weakly magnetic heated object. It is thought that even if the input current is 1, the detection level detected by the current transformer will be lower when heating a weakly magnetic object, and the control will work to increase the input power. .

2) Means for Solving the Problems The induction heating device of the present invention includes an input current detection means for detecting the input current to the device, and a detection level of the input current detection means so as to be equal to a predetermined set level (2). A control circuit that controls the operating state of the switching element, and turning on the switching element.

and suppressing means for suppressing the input current to the device as the OFF period becomes shorter.

e) When a pot made of weakly magnetic three-layer stainless steel or the like is used as the object to be heated for flE, and the oscillation frequency of the induction heating device increases, the above-mentioned suppressing means suppresses the input current to the device. Differences (differences in heating input to the pot that occurred from the second point onwards are resolved.

Figure 1 shows an embodiment of the recirculation circuit (2) of the induction heating apparatus of the present invention.
) 2 connected choke coils, (4) is a full wave rectifier circuit (2E connected bypass capacitor) through this choke coil (3). (5) is a full wave rectifier circuit (2E connected bypass capacitor). Wave rectifier circuit (2) (two connected induction heating coils, (6) is a resonant capacitor forming a resonant circuit with this induction heating coil (5), (7) is this resonant capacitor (6) i: parallel (two connected (8) indicates a switching element (70: damper diode) connected to the inverter circuit (IN), such as a transistor. ) is formed. (9) is a control circuit that compares the voltages at both ends of the induction heating coil (5) to generate the ON timing of the switching element (7), which is detected by the current transformer. The detection level is set in this circuit (9) so that the O of the switching element (7) is
Control the N time length.

FIG. 2 shows a specific circuit diagram of the control circuit (9), where (lυ is a variable resistor that changes the detection level of the current transformer 4, (US is the current transformer α
A diode that rectifies the detection signal at 1, (L3 is a smoothing capacitor that smoothes the rectified voltage at this diode,
C14) indicates the first comparator which receives the smoothing capacitor α4 output at the e input terminal, and the voltage level adjusted by the output operation means (L51) is input to the input terminal. (LE9 is the above-mentioned A holding capacitor that holds the average voltage of the first comparator (14) output.

1'rI is a second comparator that inputs the holding voltage of this holding capacitor field to the e input terminal (:), and a time constant circuit (total) consisting of a resistor a8 and a capacitor (ll) is connected to the e input terminal. !21) indicates a sixth comparator that compares the voltage between both ends of the heating coil (5), and when the voltage at the terminal f is lower than the voltage at the terminal e, it receives a %L level signal, and when it is reversed, it gives a 1H level signal. Outputs a signal.+2
21 is (7)'L from this third comparator 1211
' indicates a transistor that is turned off by a level signal, and this comparator c! The capacitor member is discharged from the 5Hev Pell signal C2 from No. 11.

The connection is the output from the ON timing detection circuit (211)
This is a drive circuit that turns on the switching element (7) from the second comparator (one output is from 1H' to -
When Ler-changes, the switching element (7) is set to O.
Make it FF. +241 it above ON timing detection circuit! 21) Differentiating circuit that receives the output, (C) is an inverter that inverts the output of this differentiating circuit (Ii1), (■) receives this inverter output from base C2, and connects the holding capacitor (Ii1)
This is a transistor that discharges the charge voltage of 9 through a resistor (2), and these differentiating circuits @ ~ transistor 1261
To, more.

A suppression circuit (c) is configured to suppress the input current to this device.

Next, the operation will be explained. By turning on the power switch (not shown) of the device, AC power (1) is supplied, and the full-wave rectifier circuit (2) full-wave rectifies this and supplies it to the inverter (IN). At the same time, the power supply Vcc of the control circuit (9) also rises.

In the control circuit (9), the input current (2) is transmitted from the current transformer 4 through the terminals a and b and is accumulated in the capacitor a3. The signal level is compared by the first comparator (14), and when the setting signal is at a higher level than the input signal, the output of this comparator A4 is 1H-1. When the setting signal is lower than the input signal, the output of this comparator I is s [
, e. Therefore, the holding capacitor α2 is charged with an electric charge corresponding to the set signal level C2 set by the output operating means α9, and the holding capacitor (119 terminal voltage generated by this charging C2 is applied to the second comparator 17).
) e input terminal I: supplied. Also, the input terminal C2 of this second comparator σn is the ON state of the transistor.
, 0FFc supplies the capacitor (19 terminal voltage) of the time constant circuit (to) which repeats charging and discharging. Note that when this transistor (19 is turned OFF), the switching transistor (5) is turned off by the sixth comparator (21). The terminal voltage of the bypass capacitor (4) or less (
: Performed when something that has happened is detected. Also, at this time, the switching element (7) is turned ON from the drive circuit (23). After that, the second comparator ση compares the input terminal voltage with the e input terminal voltage, and the input terminal voltage with the e input terminal voltage. When it becomes lower than the voltage, a 1LI level signal is given to the drive circuit. From this (:), the drive circuit turns off the switching element. After that, the heating coil (5
) when the voltage at terminal f exceeds the voltage at terminal e, the third
The comparator Qυ outputs a 1H level, turns on the transistor, and discharges the capacitor (L→). By repeating this cycle, the inverter circuit (IN) continues to oscillate.

A outfit like this? =, when the level is set with the output operation means a9 and the enameled pot is heated, the inverter circuit (IN) is oscillated at a predetermined oscillation frequency based on the above set level and the material of the enameled pot. A heating input is applied. At this time, the ON timing detection circuit QU
ON timing detected at J (2 synchronously, the transistor (2) of the suppression circuit ball is turned on for a short time to discharge the voltage of the holding capacitor αe.

On the other hand, if a Stesonos three-layer pot with weak magnetism is used at the same setting level as above, the equivalent inductance of the heating coil (5) will be smaller than that of the enameled pot, and the switching element (7) During the OFF' period, the resonance period due to the heating coil (5) and the resonant capacitor (6E' is shortened, and the oscillation frequency of the inverter circuit (IN) is high.) Adjust the voltage level of the holding capacitor so that it is equal to the level set by the output control means 9,
Controls the ON time of the switching element (7). At this time, the oscillation frequency of the inverter circuit (IN) increases, and the input current detection sensitivity decreases due to the reasons mentioned above. As the voltage level of the capacitor H increases and the oscillation frequency of the switching circuit (' I N ) increases, the number of ON times of the transistor ■ of the above-mentioned suppression circuit (to) also increases, and the number of discharges of the holding capacitor e becomes as low as the hollow pot. The increase in the holding voltage of the holding capacitor αe is suppressed compared to the case of , the increase in the ON period of the switching element (7) is regulated, the input 1jLR, is prevented from increasing, and is maintained at the actual set level.

It should be noted that these operations (in addition, the sixth controller
l) Output (2), control voltage of switching element (7) (
d).

The input terminal voltage (h) of the second comparator 1η, the e input terminal voltage (wa, the output (j) of the differential circuit (2), and the base voltage (6) of the transistor (to)) are shown in FIG.

Here, the solid line is the enameled pot.The one-dot line is the operating chamber when a three-layer stainless steel pot is used.

In this embodiment C, a suppressor is provided to lower the holding voltage of the holding capacitor 4, but the oscillation frequency is increased 7IO (both of which increase the resistance value of υ on the variable resistor and reduce the input current detection. ■Input terminal' of the first comparator (I4) by increasing the sensitivity or operating the output operation means α4
C may be used to reduce the pressure.

G) Effects of the invention As described above, the induction heating apparatus of the present invention includes an input current detection means for detecting an input current, and a ζ2 upper switching so that the detection level of the input current detection means is equal to a predetermined set level. The control means for controlling the operating state of the element and the ON/OFF period of the switching element are shortened (:
In addition, since it has a suppressing means for suppressing the input current to this device, even if a pot with weak magnetism is used as the object to be heated, the increase in the input current can be suppressed, and the difference in material Regardless of the situation, a predetermined input can always be obtained and the device can be controlled accurately.

[Brief explanation of the drawing]

The first factor is the circuit block diagram of the induction heating device of the present invention. FIG. 2 is a circuit diagram of the control circuit, and FIG. 3 is an operation waveform diagram illustrating the operation of the apparatus of the present invention. (1)...AC power supply, (2)...full wave rectifier circuit, (
5)...Induction heating coil, (6)--Resonance capacitor, (71...Switching element, (8)...
Damper diode, (9)...Control circuit, CII...Current transformer, (lυ...Variable resistor. αri...Diode, aea...Capacitor,
Iα7) (2i) - Comparator, a... Output operation means, ■... Time constant circuit, @... Transistor, θ... Drive circuit, Problem... Suppression circuit.

Claims (1)

[Claims] 1) A DC power supply, an induction heating coil coupled to the DC power supply, a resonant capacitor forming a resonant circuit together with the induction heating coil, and switching connected to the resonant circuit to generate a resonant current in the resonant circuit. In an induction heating device that generates an oscillating current in the resonant circuit by controlling ON and OFF of the switching device, an input current detection means for detecting an input current to the device; control means for controlling the operating state of the switching element so that the detection level at the means becomes equal to a predetermined set level; and a control means for suppressing the input current to the device as the ON/OFF period of the switching element becomes shorter. An induction heating device comprising means.