JP3030738B2 - Inverter control circuit - Google Patents

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 mainly used at home.

[0002]

2. Description of the Related Art In recent years, a system in which inverter control is directly performed by a microcomputer has become mainstream. FIG. 10 is a block diagram showing the configuration of a conventional inverter control circuit of this type, and its configuration and operation will be described below.

In FIG. 10, 1 is an AC power supply, 2 is an AC power supply 1
A zero point synchronization signal circuit for generating a signal synchronized with the zero point of
Is a rectifier circuit for rectifying the AC power supply 1, and 4 is an inverter circuit, which receives an output of the rectifier circuit 3 and drives a switching element to convert it into an AC power supply having a predetermined frequency. Reference numeral 5 denotes a voltage-controlled oscillation circuit that changes the oscillation frequency of an output signal according to the magnitude of the input voltage and drives the switching element of the inverter circuit 4. Reference numeral 6 denotes a D / A conversion circuit, which outputs an analog voltage to the voltage controlled oscillation circuit 5 according to data of an input digital signal.

A reference voltage setting circuit 7 sets a reference voltage corresponding to a constant peak voltage applied to the switching element of the inverter circuit 4. Reference numeral 8 denotes a switching element applied voltage detection circuit which detects a voltage applied to the switching element of the inverter circuit 4 and holds a peak value of the detected voltage. Adjustable to voltage. Reference numeral 9 denotes an A / D conversion circuit, which converts the output voltage of the switching element applied voltage detection circuit 8 into digital data.

Reference numeral 10 denotes a control circuit, which is a zero point synchronization signal circuit 2.
, The output signal of the reference voltage setting circuit 7, and A /
The output signal of the D conversion circuit 9 is input, the output signal of the reference voltage setting circuit 7 is compared with the output signal of the A / D conversion circuit 9, and the timing of the output signal of the zero-point synchronization signal circuit 2 is obtained based on the result. Thus, the digital signal data output to the D / A conversion circuit 6 is controlled in units of one least significant bit (LSB), and the peak voltage applied to the switching element of the inverter circuit 4 is controlled to be constant.

The main circuit of the control circuit 10 is generally a one-chip microcomputer, and the A / D conversion circuit 9
May be built into the microcomputer or an external circuit. When the A / D conversion circuit 9 is built in the microcomputer, the reference voltage setting circuit 7 is often built in the microcomputer and set by a program.

[0007]

In such a conventional inverter control circuit, when a microcomputer to be used does not include an A / D conversion circuit, an external A / D conversion circuit is used.
A / D conversion circuit is required, and the number of components is very large.
In addition, when the number of components increases, a large printed wiring board is required, which increases the cost and lowers the reliability. Further, when an A / D conversion circuit is built in the microcomputer to be used, a reference voltage setting circuit is also built in the microcomputer at the same time, and the reference voltage cannot be changed on the way because the reference voltage is set by a program. There were challenges.

The present invention has been made to solve the above-mentioned problems, and has a configuration in which the number of components can be reduced even if an A / D conversion circuit is not built in a microcomputer. It is a first object of the present invention to provide an improved inverter control circuit at a low cost.

Further, according to the present invention, the detection voltage of the peak voltage applied to the switching element of the inverter circuit can be easily set in several steps, and the voltage applied to the switching element of the inverter circuit and the oscillation frequency can be easily set in several steps. It is a second object of the present invention to provide an inverter control circuit which can be set to the following.

[0010]

In order to achieve the first object, the present invention provides a zero point synchronizing signal circuit for generating a signal synchronized with a zero point of an AC power supply, a rectifying circuit for rectifying the AC power, An output of the rectifier circuit is input, a switching element is driven, an inverter circuit that converts the power to an AC power having a predetermined frequency, and an oscillation frequency of an output signal is changed according to a magnitude of an input voltage. A voltage-controlled oscillation circuit that drives a switching element of an inverter circuit, a D / A conversion circuit that outputs an analog voltage to the voltage-controlled oscillation circuit in accordance with input digital signal data,
A reference voltage setting circuit that sets a reference voltage corresponding to a value of a peak voltage applied to the switching element of the inverter circuit; and a voltage applied to the switching element of the inverter circuit, and detects a peak value of the detected voltage. A switching element applied voltage detection circuit that holds and adjusts this value to a reference voltage set by the reference voltage setting circuit; an output signal of the switching element applied voltage detection circuit; and an output signal of the reference voltage setting circuit. And a voltage comparison circuit that outputs a comparison result, an output signal of the zero-point synchronization signal circuit, and an output signal of the voltage comparison circuit, and a voltage applied to a switching element of the inverter circuit is set. If the voltage is lower than the voltage, the digital signal output to the D / A conversion circuit is output at the timing of the output signal of the zero point synchronization signal circuit. The data plus 1LSB No., if high, the voltage applied to the switching elements of the inverter circuit after waiting a certain time is lower than the set voltage,
The digital signal output to the D / A conversion circuit is held, and when high, the data of the digital signal output to the D / A conversion circuit is reduced by 1 LSB at the timing of the output signal of the zero synchronization signal circuit. Control
A control circuit for setting a peak voltage applied to a switching element of the inverter circuit to a constant value set by the reference voltage setting circuit.

According to the present invention, in order to achieve the second object, in addition to the first configuration, a detection method for setting a detection voltage of a voltage applied to a switching element of the inverter circuit to several levels is provided. It has a voltage setting circuit.

[0012]

According to the first aspect of the present invention, the control circuit receives the output signal of the zero point synchronizing signal circuit and the output signal of the voltage comparison circuit, and applies the output signal of the voltage comparison circuit to the switching element of the inverter circuit. If the peak voltage is lower than the voltage determined by adjusting the reference voltage setting circuit and the switching element applied voltage detection circuit, the digital signal data output to the D / A conversion circuit is converted to the output signal of the zero point synchronization signal circuit. +1 LSB at the timing of (1) to change the input voltage of the voltage controlled oscillation circuit by +1 LSB,
Increase the oscillation frequency of the output signal of the voltage controlled oscillator by 1 L
By changing by SB, the peak voltage applied to the switching element of the inverter circuit can be increased.

Conversely, if the peak voltage applied to the switching element of the inverter circuit is higher than the voltage determined by the adjustment of the reference voltage setting circuit and the switching element applied voltage detection circuit, after waiting for a certain time, the switching of the inverter circuit If the voltage applied to the device is lower than the set voltage,
The peak voltage applied to the switching element of the inverter circuit can be kept constant by holding the data of the digital signal output to the D / A conversion circuit. If it is high, the data of the digital signal output to the D / A conversion circuit at the timing of the output signal of the zero point synchronizing signal circuit is reduced by 1 LSB, and the input voltage of the voltage controlled oscillation circuit is changed by 1 LSB. By changing the oscillation frequency of the output signal by -1 LSB, the peak voltage applied to the switching element of the inverter circuit can be reduced.

By the above operation, the peak voltage applied to the switching element of the inverter circuit can be kept constant at a voltage determined by adjusting the reference voltage setting circuit and the switching element applied voltage detection circuit.

According to the second aspect of the present invention, in the switching element applied voltage detection circuit, the magnitude of the detection voltage of the voltage applied to the switching element of the inverter circuit can be set in several steps. Can be set in several steps.

[0016]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIGS.

FIG. 1 is a block diagram of the inverter control circuit. In FIG. 1, reference numeral 11 denotes a voltage comparison circuit which compares the output signal of the switching element applied voltage detection circuit 8 with the output signal of the reference voltage setting circuit 7. And outputs the result of the comparison. The control circuit 10 receives the output signal of the zero-point synchronization signal circuit 2 and the output signal of the voltage comparison circuit 11 and, if the voltage applied to the switching element of the inverter circuit 4 is lower than the set voltage, At the timing of the output signal of the circuit 2, the data of the digital signal to be output to the D / A conversion circuit 6 is increased by 1 LSB. When it is low, the digital signal data output to the D / A conversion circuit 6 is held. When it is high, the digital signal data output to the D / A conversion circuit 6 at the timing of the output signal of the zero-point synchronization signal circuit 2 is minus one.
The control is performed such that the LSB is performed, and the peak voltage applied to the switching element of the inverter circuit 4 is controlled to be a constant value set by the reference voltage setting circuit 7. Other blocks having the same functions as those of the conventional example shown in FIG. 10 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 2 is a specific circuit diagram of FIG.
In FIG. 2, a capacitor 21 and a coil 22 are connected to the output side of the rectifier circuit 3 and input to the inverter circuit 4. The capacitor 21 and the coil 22 prevent the noise generated in the inverter circuit 4 from affecting the AC power supply 1. The inverter circuit 4 includes a noise prevention capacitor 4a,
It comprises a resonance capacitor 4b, a resonance coil 4c, an IGBT 4d as a switching element, and a protection diode 4e for a reverse voltage. The voltage controlled oscillation circuit 5 changes the oscillation frequency of the output signal according to the magnitude of the input voltage, and drives the IGBT 4 d that is a switching element of the inverter circuit 4.

The D / A conversion circuit 6 outputs an analog voltage to the voltage controlled oscillation circuit 5 according to the data of the input digital signal. The reference voltage setting circuit 7 sets a reference voltage corresponding to a constant value of the peak voltage applied to the IGBT 4d which is a switching element of the inverter circuit 4. The reference voltage setting circuit 7 is composed of a resistor 7a, a diode 7b for temperature compensation, a resistor 7c, and a resistor 7d. A resistor 7a and a diode 7b are connected in series, and a reference voltage V divided by the resistor 7c. _C1 is the voltage comparison circuit 11 (+)
Input to the terminal. The resistor 7d is connected between the (+) terminal of the voltage comparison circuit 11 and the output terminal of the voltage comparison circuit 11 in order to give the reference voltage a hysteresis characteristic.

The switching element applied voltage detection circuit 8
IGBT4 which is a switching element of inverter circuit 4
The voltage applied to d is divided by the resistors 8a and 8b, and the divided voltage is divided by the variable resistor 8c, the series resistor of the resistor 8d, and the resistor 8e, and this voltage is divided by the resistor 8f, the transistor 8g, It is input to a peak hold circuit composed of a resistor 8h and a capacitor 8i. The output voltage V _B1 of this peak hold circuit is input to the (−) terminal of the voltage comparison circuit 11. The microcomputer constituting the control circuit 10 uses the DC power supply circuit 24 as a power supply, inputs the output signal of the zero-point synchronization signal circuit 2 and the output signal V _D1 of the voltage comparison circuit 11,
The digital signal data is output to the D / A conversion circuit 6. The capacitor 23 is connected to prevent noise from the AC power supply 1. The DC power supply circuit 24 receives the AC power supply 1 and generates a stable DC power supply.

The operation of the above configuration will be described with reference to the flowchart of FIG. Step (hereinafter abbreviated as S) 30
Let us consider a cooking pot as a load placed on the resonance coil 4c of the inverter circuit 4. The power input to this pot is P _in , and the set power to be input to this pot is P _w . If the voltage P _in that is input to the pot is different from the set power P _w, the process proceeds to start from the fact that to adjust S31. In S31, the power P _in is input to the pot is larger than the set power P _w, the process proceeds to S32. In S32, the variable resistor 8c is adjusted to reduce the resistance value, the voltage V _B1 across the capacitor 8i is increased, the output of the voltage comparison circuit 11 is set to low level, and the process proceeds to S34. S34 is processed in subroutine A.

[0022] In contrast to S31, if the power P _in that is input to the pot is smaller than the set power P _w, the process proceeds to S33. In S33,
The variable resistor 8c is adjusted to increase the resistance value, reduce the voltage V _B1 across the capacitor 8i, set the output of the voltage comparison circuit 11 to a high level, and proceed to S34. S34
Is processed in the subroutine A. After S34, the process returns to S30.

[0023] In S30, and the power P _in that is input to the pot, if the same as the set power P _w, the process proceeds to S35, the adjustment of the variable resistor 8c is completed. The process proceeds from S35 to S36. S36 is processed in subroutine A, and this is continued.

Next, the operation of the subroutine A will be described with reference to the flowchart of FIG. In step S40, the control circuit 10 (hereinafter referred to as a microcomputer) changes the voltage V _B1 to the voltage V _B1.
Control if greater than _C1 . That is, if the output is at the low level of the voltage comparator circuit 11, a voltage V _B1 increases, the output of the voltage comparator circuit 11 if a high level, it is determined that the voltage V _B1 small. If the voltage V _B1 is higher than the voltage V _C1 in S40, the process proceeds to S41. In S41

[0025]

[Outside 1]

It is determined by the operating speed of the data 10.

Next, the process proceeds to S42. In S42, the microcomputer 10 determines whether the voltage V _B1 is higher than the voltage V _C1 . That is, when the output of the voltage comparison circuit 11 is at a low level, it is determined that the voltage V _B1 is large, and when the output of the voltage comparison circuit 11 is at a high level, the voltage V _B1 is determined to be small. If the voltage V _B1 is smaller than the voltage V _{C1 in} S42, the process proceeds to S43. In S43, the microcomputer 10 holds the digital signal data to be output to the D / A conversion circuit 6, and ends the subroutine A.

If the voltage V _B1 is higher than the voltage V _{C1 in} S42, the process proceeds to S44. In S44, the output signal (ZVP) of the zero point synchronizing signal circuit 2 maintains the state up to now except for the zero point of the AC power supply 1, and when a signal indicating the zero point comes,
Continue to 45. In S45, the microcomputer 10 sets the D /
The data of the digital signal output to the A conversion circuit 6 is changed by minus 1 LSB, and the process proceeds to S46. In S46, since the data of the input digital signal has decreased by -1 LSB, the output voltage of the D / A conversion circuit 6 decreases.

Next, the process proceeds to S47. In S47, since the voltage input to the voltage controlled oscillation circuit 5 increases, the voltage controlled oscillation circuit 5 increases the oscillation frequency f by keeping the off time of the output signal constant and shortening the on time. That is, the ON time of the IGBT 4d is shortened, and the power input to the pan is reduced. Next, the process proceeds to S48. In S48, S47
Then, by shortening the ON time of the IGBT 4d,
The peak voltage applied to the IGBT 4d decreases, and the voltage V _B1 across the capacitor 8i also decreases. The subroutine A ends from S48.

Next, if the voltage V _B1 is smaller than the voltage V _{C1 in} S40, the process proceeds to S49. In S49, the output signal (ZVP) of the zero-point synchronizing signal circuit 2 maintains the state up to now except for the zero point of the AC power supply 1, and when a signal indicating the zero point comes, the process proceeds to S50. In S50, the microcomputer 10
Changes the data of the digital signal output to the D / A conversion circuit 6 by 1 LSB, and proceeds to S51. In S51, since the data of the input digital signal has increased by 1 LSB, the output voltage of the D / A conversion circuit 6 increases.

Next, the process proceeds to S52. In S52, since the voltage input to the voltage controlled oscillation circuit 5 increases, the voltage controlled oscillation circuit 5 lowers the oscillation frequency f by making the off time of the output signal constant and lengthening the on time. That is, the ON time of the IGBT 4d becomes longer, and the electric power input to the pot increases. Next, the process proceeds to S53. In S53, S52
Then, because the on-time of the IGBT 4d is longer,
The peak voltage applied to the IGBT 4d increases, and the voltage V _B1 across the capacitor 8i also increases. Subroutine A is ended from S53.

With the above operation, the microcomputer
Even if the A / D conversion circuit 9 shown in FIG. 10 is not built in FIG. 10, the inverter circuit 4 is controlled by a simple circuit with a small number of parts, and the peak voltage applied to the switching element of the inverter circuit 4 is The reference voltage setting circuit 7 and the switching element applied voltage detection circuit 8 can maintain a constant voltage determined by the adjustment, can supply a constant power to the cooking pot, realize a small printed wiring board, It is intended to realize an inverter control circuit with improved reliability and low cost.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5, 6, 7, 8 and 9. FIG. 5 is a block diagram of the inverter control circuit. In FIG. 5, reference numeral 12 denotes a detection voltage setting circuit.
Of the voltage applied to the switching element is set to several levels. The control circuit 10 outputs an output signal to the detection voltage setting circuit 12, receives an output signal of the zero point synchronization signal circuit 2 and an output signal of the voltage comparison circuit 11, and outputs a voltage applied to a switching element of the inverter circuit 4. Is lower than the set voltage, the data of the digital signal output to the D / A conversion circuit 6 is increased by 1 LSB at the timing of the output signal of the zero point synchronization signal circuit 2; If the voltage applied to the switching element is lower than the set voltage, the data of the digital signal output to the D / A conversion circuit 6 is held,
When it is high, the digital signal output to the D / A conversion circuit 6 is controlled so as to be reduced by 1 LSB at the timing of the output signal of the zero point synchronization signal circuit 2 so that the peak voltage applied to the switching element of the inverter circuit 4 is reduced. It can be controlled so as to be a constant value set by the detection voltage setting circuit 12. Further, the constant value of the peak voltage applied to the switching element of the inverter circuit can be set in several steps. Other blocks having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 6 is a specific circuit diagram of FIG.
2 is similar to FIG. 2, except that a resistor 12a forms a detection voltage setting circuit 12, one terminal of the resistor 12a is a base terminal of the transistor 8g, and the other terminal is an output of the microcomputer 10. Connected to terminal. In accordance with the state of the output terminal of the microcomputer 10, the inverter circuit 4
The magnitude of the detected voltage that is obtained by detecting the voltage applied to the switching element is set in two stages.

The operation in the above configuration is shown in the flow chart of FIG. 7 and is the same as that of FIG. 3, wherein the voltage V _B1 is shown as the voltage V _B2 and the subroutine A is shown as B. S80
Consider a cooking pot with the inverter circuit 4 as a load placed on the resonance coil 4c. _Let P _in be the power input to this pot and P _wH be the set power you want to input to this pot. Here, the microcomputer 10 sets the output terminal to which the resistor 12a is connected to a low level, and sets a peak voltage applied to the switching element of the inverter circuit 4 in _accordance with the set power P _wH .

Next, the process proceeds to S81. If the power _Pin input to the pot is different from the set power _{PwH in} S81, the adjustment is started and the process proceeds to S82. In S82, the power P _in is input to the pot, when greater than the set power P _wH, the process proceeds to S83.
In S83, the variable resistor 8c is adjusted to reduce the resistance value, the voltage _VB2 across the capacitor 8i is increased, the output of the voltage comparison circuit 11 is set to low level, and the process proceeds to S85. S85 is processed in subroutine B.

[0037] In contrast to S82, the power P _in is input to the pot,
When it is smaller than the set power P _wH , the process proceeds to S84. In S84, the variable resistor 8c is adjusted to increase the resistance value, the voltage _VB2 across the capacitor 8i is reduced, and the voltage comparison circuit 11
Is set to the high level, and the process proceeds to S85. S85
Is processed in the subroutine B. After S85, the process returns to S81. In S81, and the power P _in that is input to the pot, set power P
If it is the same as _wH , the process proceeds to S86, and the adjustment of the variable resistor 8c is completed. The process proceeds from S86 to S87. S87 is processed in subroutine B, and this is continued.

Next, the operation of the subroutine B is shown in the flowchart of FIG. 8, which is the same as that of FIG.
_B1 is shown as voltage V _B2 , and voltage V _C1 is shown as voltage V _C2 . S90
The microcomputer 10 determines that the voltage V _B2 is equal to the voltage V _C2
Determine if it is greater than. That is, if the output is at the low level of the voltage comparator circuit 11, the voltage V _B2 increases, the output of the voltage comparator circuit 11 if a high level, it is determined that the voltage V _B2 small. In S90

[0039]

[Outside 2]

The machine is operated. The time t is as short as possible and is determined by the operating speed of the microcomputer 10.

Next, the process proceeds to S92. In S92, the microcomputer 10 determines whether the voltage V _B2 is higher than the voltage V _C2 . That is, when the output of the voltage comparison circuit 11 is at a low level, it is determined that the voltage V _B2 is large, and when the output of the voltage comparison circuit 11 is at a high level, the voltage V _B2 is determined to be small. If the voltage V _B2 is smaller than the voltage V _{C2 in} S92, the process proceeds to S93. S93
Then, the microcomputer 10 holds the data of the digital signal to be output to the D / A conversion circuit 6, and ends the subroutine B.

If the voltage V _B2 is higher than the voltage V _{C2 in} S92, the process proceeds to S94. In S94, the output signal (ZVP) of the zero point synchronizing signal circuit 2 maintains the state up to now except for the zero point of the AC power supply 1, and when a signal indicating the zero point comes, S94.
Go to 95. In S95, the microcomputer 10 sets the D /
The data of the digital signal output to the A conversion circuit 6 is changed by -1 LSB, and the process proceeds to S96. In S96, since the data of the input digital signal has decreased by -1 LSB, the output voltage of the D / A conversion circuit 6 decreases.

Next, the process proceeds to S97. In S97, since the voltage input to the voltage controlled oscillation circuit 5 increases, the voltage controlled oscillation circuit 5 increases the oscillation frequency f by keeping the off time of the output signal constant and shortening the on time. That is, the ON time of the IGBT 4d is shortened, and the power input to the pan is reduced. Next, the process proceeds to S98. In S98, S97
Then, by shortening the ON time of the IGBT 4d,
The peak voltage applied to the IGBT 4d decreases, and the voltage V _B2 across the capacitor 8i also decreases. The subroutine B is ended from S98.

If the voltage V _B2 is smaller than the voltage V _{C2 in} S90, the process proceeds to S99. In S99, the output signal (ZVP) of the zero point synchronizing signal circuit 2 maintains the state up to now except for the zero point of the AC power supply 1, and when a signal indicating the zero point comes, the process proceeds to S100. In S100, the microcomputer 10
Changes the data of the digital signal output to the D / A conversion circuit 6 by 1 LSB, and proceeds to S101. In S101,
Since the data of the input digital signal has increased by 1 LSB, the output voltage of the D / A conversion circuit 6 increases.

Next, the process proceeds to S102. In S102, since the voltage input to the voltage controlled oscillation circuit 5 increases, the voltage controlled oscillation circuit 5 lowers the oscillation frequency f by keeping the off time of the output signal constant and lengthening the on time. That is, the ON time of the IGBT 4d becomes longer, and the electric power input to the pot increases. Next, the process proceeds to S103. In S103,
In S102, since the on-time of the IGBT 4d is increased, the peak voltage applied to the IGBT 4d increases, and the voltage V _B2 across the capacitor 8i also increases. S103
From the subroutine B.

Next, the operation of the detection voltage setting circuit 12 will be described with reference to the flowchart of FIG. At S110, the input voltage P
_It is determined whether or not _in is set to the set power P _wH . Here the state of the inverter control circuit, the adjustment completion state of S86 in the flowchart of FIG. 7, the input power P _in is one that has been adjusted to the set power P _wH. When the input power _Pin is set to the set power _{PwH in} S110, the process proceeds to S111, and the microcomputer 10 sets the output terminal to which the resistor 12a is connected to a low level. Next, the process proceeds to subroutine B of S113. Here, the input power P _in is a set power P _wH. The process returns from S113 to S110.

When the input power _Pin is set to the set power _{PwL in} S110, the process proceeds to S112, where the microcomputer 10
Opens the output terminal to which the resistor 12a is connected. When open, the detection voltage of the voltage applied to the IGBT 4d, which is the switching element of the inverter circuit 4, in the switching element applied voltage detection circuit 8 increases, and the output voltage V _{B2 of the} switching element applied voltage detection circuit 8 increases.

The process proceeds from S112 to subroutine B of S113.
In the subroutine B of S113, since the output voltage V _{B2 of} the switching element applied voltage detection circuit 8 increases, the routine passes from S90 to S92 and S94 to S98 in FIG. As a result, the voltage applied to the IGBT 4d, which is the switching element of the inverter circuit 4, can be _reduced, and can be set to the set power P _wL smaller than the input voltage P _wH . Here, the detection voltage setting circuit 12 is set in two stages, but a resistor is added to the base terminal of the transistor 8g and another output terminal of the microcomputer 10 to increase the number of setting stages of the detection voltage setting circuit 12. It is also possible.

With the above operation, the microcomputer
Even if the A / D conversion circuit is not built in the inverter circuit 4, the inverter circuit 4 is controlled by a simple circuit having a small number of parts, and the peak voltage applied to the switching element of the inverter circuit 4 is changed by the reference voltage setting circuit 7. And the switching element applied voltage detection circuit 8 can be adjusted and the voltage determined by the detection voltage setting circuit 12 can be kept constant, a constant power can be supplied to the cooking pot, and the printed wiring board can be downsized. The present invention realizes an inverter control circuit with improved reliability and low cost.

Further, since the detection voltage of the peak voltage applied to the switching element of the inverter circuit 4 can be easily set in several steps, the voltage and the oscillation frequency applied to the switching element IGBT 4d of the inverter circuit 4 can be easily set in several steps. The present invention realizes an inverter control circuit that can be set to the following.

[0051]

As described above, the inverter control circuit according to the present invention can keep the peak voltage applied to the switching element of the inverter circuit constant with a simple circuit configuration, and can provide the microcomputer with an A / D conversion circuit. Therefore, even when the device is not built-in, the number of components can be reduced, so that the printed wiring board can be downsized, the reliability can be improved, and a low-cost inverter control circuit can be realized.

Further, the detection voltage of the peak voltage applied to the switching element of the inverter circuit can be set in several steps, and can be easily changed. The voltage applied to the switching element of the inverter circuit and the load applied to the load can be easily changed. It is possible to realize an inverter control circuit that can set the input voltage and the oscillation frequency in several steps and can easily change the input voltage and the oscillation frequency.

[Brief description of the 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 specific circuit diagram of the inverter control circuit of FIG.

FIG. 3 is a flowchart showing the operation of FIG. 2;

FIG. 4 is a flowchart showing an operation of a subroutine A of FIG. 3;

FIG. 5 is a block diagram of an inverter control circuit according to a second embodiment of the present invention.

FIG. 6 is a specific circuit diagram of the inverter control circuit of FIG.

FIG. 7 is a flowchart showing the operation of FIG.

8 is a flowchart showing an operation of a subroutine B of FIG.

FIG. 9 is a flowchart showing an operation of the detection voltage setting circuit of FIG. 5;

FIG. 10 is a block diagram showing a configuration of a conventional inverter control circuit.

[Explanation of symbols]

1: AC power supply, 2: Zero point synchronization signal circuit, 3: Rectifier circuit, 4: Inverter circuit, 5: Voltage controlled oscillator circuit,
6 D / A conversion circuit 7 Reference voltage setting circuit 8
... Switching element applied voltage detection circuit, 10 ... Control circuit
(Microcomputer), 11… voltage comparison circuit, 12…
Detection voltage setting circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05B 6/12 H02M 7/48

Claims (2)

(57) [Claims] 1. A zero point synchronizing signal circuit for generating a signal synchronized with a zero point of an AC power supply, a rectifier circuit for rectifying the AC power supply, an output of the rectifier circuit being input, a switching element being driven, and An inverter circuit that converts the frequency into AC power; a voltage-controlled oscillation circuit that changes the oscillation frequency of the output signal according to the magnitude of the input voltage to drive a switching element of the inverter circuit; A D / A conversion circuit that outputs an analog voltage to the voltage controlled oscillation circuit in accordance with signal data; and a reference voltage setting that sets a reference voltage corresponding to a peak voltage value applied to a switching element of the inverter circuit. Circuit, a voltage applied to a switching element of the inverter circuit is detected, and a peak value of the detected voltage is held;
A switching element applied voltage detection circuit whose value can be adjusted to a reference voltage set by the reference voltage setting circuit,
An output signal of the switching element applied voltage detection circuit;
A voltage comparison circuit that compares an output signal of the reference voltage setting circuit and outputs a comparison result, an output signal of the zero-point synchronization signal circuit, and an output signal of the voltage comparison circuit,
When the voltage applied to the switching element of the inverter circuit is lower than the set voltage, the data of the digital signal output to the D / A conversion circuit is increased by 1 LSB at the timing of the output signal of the zero-point synchronization signal circuit, and is increased. If the voltage applied to the switching element of the inverter circuit is lower than a set voltage after waiting for a certain time, the digital signal data to be output to the D / A conversion circuit is held. The digital signal data output to the D / A converter circuit at the timing of the output signal is set to minus 1 LSB, and the peak voltage applied to the switching element of the inverter circuit is set by the reference voltage setting circuit. And a control circuit for setting a constant value. 2. The inverter control circuit according to claim 1, further comprising a detection voltage setting circuit for setting a detection voltage obtained by detecting a voltage applied to a switching element of the inverter circuit to several levels. .