JPH05343175A - Inverter control circuit - Google Patents

Abstract

PURPOSE:To perform a safe control even in the state with no load by providing a comparing circuit for comparing the output of a current detecting circuit with a fixed standard level and outputting the comparision result, an inverter circuit, and a control circuit. CONSTITUTION:A comparing circuit 15 is formed of a resistance for dividing the DC voltage of a DC power source for inputting an AC power source 10 and outputting DC voltage to set a standard voltage; and a voltage comparator for comparing the standard voltage with the output voltage of a current detecting circuit 14. When a control circuit 16 outputs a drive signal to an inverter circuit 12 in the case having no load, the value of the current supplied from the power source 10 by the circuit 14 is detected, and this detection signal is inputted to the circuit 15. The circuit 15 detects that the current value is smaller than a fixed level through the comparator, and stops the drive signal outputted to the circuit 12. Thus, a safe inverter control circuit can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control circuit for an electromagnetic cooker or the like.

[0002]

2. Description of the Related Art In recent years, electromagnetic induction heating has attracted attention as a safe heat source, and a method of directly controlling an inverter of an electromagnetic cooker by a microcomputer has become mainstream. In addition, the electric power input to the load is not constant but can be set in several steps, which is becoming the mainstream. Conventionally, this type of inverter control circuit has a configuration as shown in FIG. The configuration and operation will be described below with reference to FIG.

In FIG. 7, 1 is an AC power supply, 2 is a rectifier circuit for rectifying the AC power supply 1, 3 is an input of the output of the rectifier circuit 2, and a switching element is driven to provide a predetermined circuit by a resonance circuit of a heating coil and a capacitor. Inverter circuit for converting into AC power of frequency, 4 is a load that is induction-heated with constant power by the magnetic field of the heating coil of the inverter circuit 3, 5 outputs a drive signal to the inverter circuit 3, and inputs power to the load 4. It is a control circuit for controlling whether to input or not input.

[0004]

In the conventional inverter control circuit composed of such components, when the control circuit 5 outputs a signal for driving the inverter circuit 3 in the absence of the load 4, the inverter circuit 3 is driven. There is a problem that stress is applied to the circuit elements such as the switching element and the capacitor that compose the above, and in the worst case, the switching element may be destroyed and stop functioning, leading to an accident.

The present invention solves the above problems, and a first object of the present invention is to provide a safe inverter control circuit even when there is no load. A second object of the present invention is to provide a safe inverter control circuit even when there is no load when the power input to the load can be set in several steps.

[0006]

In order to achieve the first object, the present invention provides an AC power supply, a rectifying circuit for rectifying the AC power supply, and an input of the output of the rectifying circuit to drive a switching element. And a load that is induction-heated with constant power by the magnetic field of the heating coil of the inverter circuit, and is supplied from the AC power supply. Current detection circuit for detecting the current value, a comparison circuit for comparing the output of the current detection circuit with a constant reference level and outputting a comparison result, and an output of the comparison circuit for outputting a drive signal to the inverter circuit. If the current value supplied from the AC power supply is less than a certain value, it is determined that there is no load and the drive signal output to the inverter circuit is stopped. It has a configuration that includes a that control circuit.

In order to achieve the second object, the present invention provides an AC power supply, a rectifying circuit for rectifying the AC power supply,
An inverter circuit that inputs the output of the rectifier circuit and drives a switching element to convert into an AC power source of a predetermined frequency in several steps by a resonance circuit of a heating coil and a capacitor, and power of several steps by a magnetic field of the heating coil of the inverter circuit. A load that is induction-heated by the AC power supply, a current detection circuit that detects a current value supplied from the AC power supply, and a comparison circuit that compares the output of the current detection circuit with a reference level and outputs a comparison result. A reference setting circuit capable of setting the reference level of the comparison circuit in several stages corresponding to the power input to the load, and outputting the reference level of the comparison circuit to the power input to the load. The level is set, the drive signal is output to the inverter circuit, the output of the comparison circuit is input, and the current value supplied from the AC power supply is less than or equal to a set value. Ba said determined load is the absence has a configuration in which a control circuit for stopping the drive signal being output to the inverter circuit.

[0008]

According to the present invention, in the first configuration, when the control circuit provides the drive signal to the inverter circuit when there is no load, the current detection circuit detects the value of the current supplied from the AC power source. The detection signal is input to the comparison circuit, and the comparison circuit detects that the current value is smaller than a certain level,
The control circuit that receives the output of the comparison circuit determines that there is no load, and stops the drive signal that is output to the inverter circuit.

In the second structure of the present invention, the control circuit outputs a signal to the reference setting circuit and sets the reference level corresponding to the value of the electric power input to the load in the comparison circuit, and when there is no load. When the control circuit gives a drive signal to the inverter circuit, the current detection circuit detects the value of the current supplied from the AC power source, inputs this detection signal to the comparison circuit, and sets the reference level set by the reference setting circuit. The control circuit that has received the output of the comparison circuit determines that there is no load, and stops the drive signal output to the inverter circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIGS.

FIG. 1 is a first block diagram of the present invention.
In FIG. 1, 10 is an AC power supply, 11 is a rectifying circuit for rectifying the AC power supply 10, 12 is an input of the output of the rectifying circuit 11, drives a switching element, and uses a resonance circuit of a heating coil and a capacitor to provide an AC power supply of a predetermined frequency. An inverter circuit for converting into a load, 13 is a load that is induction-heated with a constant power by the magnetic field of the heating coil of the inverter circuit 12, 14 is a current detection circuit that detects the current value supplied from the AC power supply 10, and 15 is a current detection circuit 14 16 is a control circuit, which is a control circuit that compares the output of the
The drive signal is output to 12 and the output of the comparison circuit 15 is input, and if the current value supplied from the AC power supply 10 is below a certain value, it is determined that there is no load 13 and is output to the inverter circuit 12. The drive signal is controlled to stop.

FIG. 2 is a circuit diagram of the first embodiment of the present invention. In FIG. 2, 10 is an AC power supply, 11 is an AC power supply 10
A rectifier circuit for rectifying the current, 12 is an inverter circuit for inputting the output of the rectifier circuit 11, driving a switching element, and converting it into an AC power supply of a predetermined frequency by a resonance circuit of a heating coil and a capacitor (not shown), A load that is induction-heated with a constant electric power by the magnetic field of the heating coil of the inverter circuit 12, such as a stainless steel pot. Reference numeral 14 is a current detection circuit that detects the value of the current supplied from the AC power supply 10. The current transformer 14a is connected between one side of the AC power supply 10 and the rectifier circuit 11 and the resistor connected to the output of the current transformer 14a. 14b, a rectifier circuit 14c for rectifying the output voltage of the current transformer 14a, and a capacitor 14d for smoothing the output of the rectifier circuit 14c. 15 is a current detection circuit 14
Is a comparator circuit for comparing the output of the AC power supply 10 with a constant reference level and outputting a comparison result. The resistor 15a for setting the reference voltage by dividing the DC voltage of the DC power supply 19 that inputs the AC power supply 10 and outputs the DC voltage. , 15b, a voltage comparator 15c for comparing the output voltage of the current detection circuit 14 with a reference voltage set by the resistors 15a, 15b, and a pull-up resistor 15d.
Reference numeral 16 denotes a microcomputer, which outputs a drive signal to the inverter circuit 12 and inputs the output of the comparison circuit 15.
The capacitor 17 and the coil 18 reduce the influence of noise of the inverter circuit 12 on the AC power supply 10 side.

The operation of the first inverter control circuit including the above components will be described with reference to the flowchart of FIG. In step 20, the microcomputer
Reference numeral 16 gives a drive signal to the inverter circuit 12, operates the inverter circuit 12, and drives the switching element at a constant oscillation frequency by the resonance of the heating coil and the capacitor of the inverter circuit 12. So if there is a load 13,
The load 13 is induction-heated with constant power by the magnetic field of the heating coil, and current is supplied from the AC power supply 10. When there is no load 13, almost no current is supplied from the AC power supply 10. Then proceed to step 21. In step 21, when the load 13 is present, current is supplied from the AC power supply 10, so the output voltage of the current transformer 14a is equal to the flowing current value and the resistance.
The voltage is determined by the value of 14b. Rectifier circuit 14c
The voltage rectified by and smoothed by the capacitor 14d is compared with the comparison circuit 15
Is input to the positive terminal of the voltage comparator 15c and compared with the reference voltage set by the resistors 15a and 15b of the negative terminal. Here, the reference voltage is the minimum current value 11 flowing from the AC power supply 10 when the load 13 is present and the AC power supply 10 when the load 13 is not present.
Is set to a voltage at which the maximum current value 12 flowing from can be determined, and is usually set to a voltage corresponding to an intermediate value between the current values 11 and 12. Thus, when the load 13 is present, the voltage at the positive terminal of the voltage comparator 15c becomes higher than the voltage at the negative terminal, and the output of the voltage comparator 15c becomes high level. The microcomputer 16 inputs this signal, the current supplied from the AC power supply 10 is equal to or more than the set current value set in the negative terminal of the voltage comparator 15c, and the load 13
If so, the process proceeds to step 20 to continue the heating operation. When there is no load 13 in step 21, almost no current is supplied from the AC power supply 10, so the current transformer 14
The output voltage of "a" becomes a value close to 0 volt, and the voltage comparator 15c of the comparison circuit 15 has almost 0 at the positive terminal.
A value close to the bolt is input and the negative terminal resistance 15a, 15
It is compared with the reference voltage set in b. Here, the reference voltage is set to a voltage at which the minimum current value 11 that flows from the AC power supply 10 when there is a load 13 and the maximum current value 12 that flows from the AC power supply 10 when there is no load 13 are set. Normally, it is set to a voltage corresponding to an intermediate value between the current value 11 and the current value 12. As a result, when there is no load 13, the voltage comparator 15c
The voltage of the positive terminal of the voltage comparator 15c becomes lower than the voltage of the negative terminal, and the output of the voltage comparator 15c becomes low level. The microcomputer 16 inputs this signal, determines that the current supplied from the AC power supply 10 is smaller than the set current value set in the negative terminal of the voltage comparator 15c, and that the load 13 is not present. Go to 22 Inverter circuit 12
Stop the drive signal to and stop the heating operation.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4, 5 and 6. FIG. 4 is a second block diagram of the present invention. In FIG. 4, 30 is an AC power supply, 31 is a rectifier circuit that rectifies the AC power supply 30, and 32 is a rectifier circuit.
An inverter circuit that inputs the output of 31 and drives a switching element to convert it into an AC power supply of a predetermined frequency of several steps by a resonance circuit of a heating coil and a capacitor, 33 is a power of several steps by the magnetic field of the heating coil of the inverter circuit 32. Is a load that is induction heated by 34, 34 is a current detection circuit that detects the current value supplied from the AC power supply 30, 35 is a comparison circuit that compares the output of the current detection circuit 34 with a reference level, and outputs a comparison result, and 36 is a load A reference setting circuit that can set the reference level of the comparison circuit 35 in several stages corresponding to the power input to the 33, 37 is a control circuit, and outputs the reference level of the comparison circuit 35 to the load 33 by outputting to the reference setting circuit 36. Set to a level that corresponds to the input power,
The drive signal is output to the inverter circuit 32, the output of the comparison circuit 35 is input, and if the current value supplied from the AC power supply 30 is less than or equal to the set value, it is determined that there is no load 33, and the inverter circuit 32 is determined. The output drive signal is controlled to stop.

FIG. 5 is a circuit diagram of the second embodiment of the present invention. In FIG. 5, 30 is an AC power supply, 31 is an AC power supply 30.
A rectifier circuit for rectifying the input, 32 inputs the output of the rectifier circuit 31,
An inverter circuit that drives a switching element and converts into a two-stage AC power source of a predetermined frequency by a resonance circuit of a heating coil and a capacitor, and 33 is a load that is inductively heated by two-stage power by the magnetic field of the heating coil of the inverter circuit 32. Yes, such as a stainless steel pot. 34 is a current detection circuit that detects the current value supplied from the AC power supply 30.
A current transformer 34a connected between one side of 30 and the rectifier circuit 31, a resistor 34b connected to the output of the current transformer 34a, a rectifier circuit 34c for rectifying the output voltage of the current transformer 34a, and a rectifier circuit 34c. It is composed of a capacitor 34d for smoothing the output. Reference numeral 35 denotes a comparison circuit that compares the output of the current detection circuit 34 with a reference level and outputs a comparison result.The reference voltage is obtained by dividing the DC voltage of the DC power supply 40 that inputs the AC power supply 30 and outputs the DC voltage. Resistance to set
35a, 35b, the output voltage of the current detection circuit 34 and the resistor 35a,
Voltage comparator 35c for comparing with the reference voltage set by 35b
And a pull-up resistor 35d. 36 is a resistor, which corresponds to the power input to the load 33
It is a reference setting circuit capable of setting the reference level of 2 in two steps. Reference numeral 37 denotes a microcomputer, which determines the power input to the load 33, outputs a drive signal to the inverter circuit 32, outputs the drive signal to the reference setting circuit 36 corresponding to the power input to the load 33, and outputs the drive signal to the reference circuit 35. Set the reference level. Further, the output of the comparison circuit 35 is input. Capacitor 38 and
39 reduces the influence of the noise of the inverter circuit 32 on the AC power supply 30 side.

The operation of the configuration of the second embodiment will be described with reference to the flow chart of FIG. At step 50, the microcomputer 37 inputs the power P to the load 33.
W is determined, a signal is given to the inverter circuit 32 so that the electric power is input to the load 33, and the oscillation frequency of the inverter circuit 32 is set. Here, the power that can be input to the load 33 is P
There are two types, W1 and PW2, and PW1> PW2. Then proceed to step 51. In step 51, the microcomputer 37 outputs a signal to the reference voltage setting circuit 36 in response to the power determined in step 50. Ie step 50
If the power determined in step PW1 is set, the output connected to the resistor 36 is opened, and the power determined in step 50 is set to PW1.
If it is W2, the output connected to the resistor 36 is set to low level. At this time, the reference voltage of the comparison circuit 35 is the AC power source when the load 33 is present when the power is PW1 and the PW1 is input.
The minimum value of the current that flows from 30 and the maximum value of the current that flows from the AC power supply 30 when there is no load 33 are set to a voltage that can be discriminated.Normally, the voltage corresponding to the intermediate value of these current values is set. It is set. When the power is PW2,
The minimum value of the current that flows from the AC power supply 30 when there is a load 33 and PW2 is input, and the AC power supply 30 when there is no load 33
Is set to a voltage that can be discriminated from the maximum value of the current flowing from the device, and is usually set to a voltage corresponding to an intermediate value of these current values. Then proceed to step 52. Step 52
Then, the microcomputer 37 gives a drive signal to the inverter circuit 32, operates the inverter circuit 32, and drives the switching element at a constant oscillation frequency by the resonance of the heating coil and the capacitor of the inverter circuit 32. Thus, when there is the load 33, the load 33 is induction-heated by the constant electric power determined in step 50 by the magnetic field of the heating coil, and the AC power supply 30 supplies a current according to the electric power. load
When there is no 33, almost no current is supplied from the AC power supply 30. Then proceed to step 53. Load in step 53
When there is 33, current is supplied from the AC power supply 30, so the output voltage of the current transformer 34a is
The voltage is determined by the resistor 34b. This voltage is rectified by the rectifier circuit 34c
The voltage rectified by and smoothed by the capacitor 34d is compared with the comparison circuit 35.
Is input to the positive terminal of the voltage comparator 35c and compared with the reference voltage set by the resistors 35a, 35b and the resistor 36 at the negative terminal. Here, the reference voltage is the voltage set in step 51, and when the load 33 is present, the voltage at the positive terminal of the voltage comparator 35c becomes higher than the voltage at the negative terminal, and the output of the voltage comparator 35c becomes , High level. The microcomputer 37 inputs this signal, the current supplied from the AC power supply 30 is equal to or more than the set current value set in the negative terminal of the voltage comparator 35c, it is determined that there is a load 33, and the process proceeds to step 50. Continue heating operation. When there is no load 33 in step 53, almost no current is supplied from the AC power supply 30, so the output voltage of the current transformer 34a becomes a value close to 0 volt, and the positive terminal of the voltage comparator 35c of the comparison circuit 35 is A value close to 0 volt is input and compared with the reference voltage set by the resistors 35a, 35b and the resistor 36 at the negative terminals. Here, the reference voltage is the voltage set in step 51, and the load 33
When there is no voltage, the voltage at the positive terminal of the voltage comparator 35c becomes lower than the voltage at the negative terminal, and the output of the voltage comparator 35c becomes low level. This signal is sent to the microcomputer
37 is input, the current supplied from the AC power supply 30 is smaller than the set current value set in the negative terminal of the voltage comparator 35c, and it is determined that the load 33 is not present.
Proceeding to 54, the drive signal to the inverter circuit 32 is stopped, and the heating operation is stopped. In the present embodiment, the electric power input to the load 33 is described as two kinds, but any kind of electric power may be used, and the resistance of the reference setting circuit 36 is added to correspond to each electric power, and the reference voltage of the comparison circuit 35 is added. Can be set.

[0017]

As is apparent from the first embodiment described above, according to the present invention, the current value supplied from the AC power supply is detected by the current detection circuit, and this value is compared with the reference voltage by the comparison circuit. As a result, it is possible to provide a safe inverter control circuit by detecting the absence of load and stopping the drive signal to the inverter circuit.

Further, as is apparent from the second embodiment, according to the present invention, when the electric power input to the load can be set in several steps, the reference voltage of the comparison circuit corresponds to the electric power by the reference setting circuit at any electric power. The current value supplied from the AC power supply is detected by the current detection circuit and this value is compared with the reference voltage of the comparison circuit to detect the absence of load and stop the drive signal to the inverter circuit. And a safe inverter control circuit can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an inverter control circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of the inverter control circuit.

FIG. 3 is a flowchart showing the operation of the inverter control circuit.

FIG. 4 is a block diagram of an inverter control circuit according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of the inverter control circuit.

FIG. 6 is a flowchart showing the operation of the inverter control circuit.

FIG. 7 is a block diagram of a conventional inverter control circuit.

[Explanation of symbols]

 10 AC power supply 11 Rectifier circuit 12 Inverter circuit 13 Load 14 Current detection circuit 15 Comparison circuit 16 Control circuit

Claims (2)

[Claims] 1. An AC power supply, a rectifier circuit for rectifying the AC power supply, and an output of the rectifier circuit is input to drive a switching element to replace the AC power supply with a predetermined frequency by a resonance circuit of a heating coil and a capacitor. An inverter circuit,
A load that is induction-heated with constant power by the magnetic field of the heating coil of the inverter circuit, a current detection circuit that detects a current value supplied from the AC power supply, and an output of the current detection circuit and a constant reference level. If the current value supplied from the AC power supply is less than a certain value, the load is output if the drive circuit outputs a drive signal to the inverter circuit and inputs the output of the comparison circuit to And a control circuit that determines that the drive signal is being output to the inverter circuit. 2. An alternating current power supply, a rectifying circuit for rectifying the alternating current power supply, and a switching element driven by inputting the output of the rectifying circuit to form an alternating current power supply having a predetermined frequency in several stages by a resonance circuit of a heating coil and a capacitor. An inverter circuit for conversion, a load that is induction-heated with electric power of several stages by a magnetic field of a heating coil of the inverter circuit, a current detection circuit that detects a current value supplied from the AC power supply, and an output of the current detection circuit. A reference setting circuit that compares the reference levels and outputs a comparison result; and a reference setting circuit that can set the reference level of the comparison circuit in several stages corresponding to the power input to the load; and output to the reference setting circuit Then, the reference level of the comparison circuit is set to a level corresponding to the power input to the load, a drive signal is output to the inverter circuit, and the output of the comparison circuit is output. And a control circuit for stopping the drive signal being output to the inverter circuit when the load is input and the current value supplied from the AC power source is less than or equal to a set value. Inverter control circuit.