JP2976632B2 - 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 method of directly controlling an inverter by a microcomputer has become mainstream.

Conventionally, this kind of inverter control circuit is shown in FIG.
The configuration is as shown in FIG. Hereinafter, the configuration and operation will be described with reference to FIG.

As shown in FIG. 5, reference numeral 2 denotes a zero point synchronization signal circuit for generating a signal synchronized with the zero point of the AC power supply 1. The output of the rectifier circuit 3 for rectifying the AC power supply 1 is input to the inverter circuit 4. The inverter circuit 4 receives the output of the control circuit 3 and drives the switching element to convert the switching element 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 controls a voltage-controlled oscillation circuit 5 in accordance with data of an input digital signal.
Output analog voltage. Reference numeral 7 denotes a reference voltage setting circuit that sets a reference voltage corresponding to a constant peak voltage applied to the switching element of the inverter circuit 4. 8
Is 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, and this value is a reference voltage set by the reference voltage setting circuit 7. Can be adjusted. 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 includes an output signal of the zero-point synchronization signal circuit 2, an output signal of the reference voltage setting circuit 7, and an A / D
The output signal of the conversion circuit 9 and the reference voltage setting circuit 7
Is compared with the output signal of the A / D conversion circuit 9, and based on the result, the data of the digital signal output to the D / A conversion circuit 6 is output at the timing of the output signal of the zero point synchronization signal circuit 2. Control is performed in units of 1 LSB (the bit having the smallest weight), and control is performed so that the peak voltage applied to the switching element of the inverter circuit 4 becomes constant. Here, the main circuit of the control circuit 10 is generally a one-chip microcomputer, and the A / D conversion circuit 9 may be built in the microcomputer or may be an external circuit. When the A / D conversion circuit 9 is built in the microcomputer, the reference voltage setting circuit 7 is also built in the microcomputer and is often set by a program.

[0005]

In such a conventional inverter control circuit, the reliability is improved and the cost is reduced.
There was a problem in providing an inverter control circuit.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an inverter for supplying commercial power to high-frequency power.
And a switching element of the inverter circuit.
A voltage-controlled oscillation circuit that operates, and
A D / A conversion circuit for outputting a analog voltage;
And a control circuit that outputs a digital signal to the conversion circuit,
The control circuit includes a pin applied to the switching element.
According to the peak voltage.
The signal is controlled to increase or decrease in units of 1 LSB.

[0007]

According to the present invention, reliability can be improved by the above configuration.
It is possible to provide a low-cost inverter control circuit
Become.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. 1, 2, 3 and 4. FIG.

FIG. 1 is a block diagram of the present invention. In FIG. 1, reference numeral 12 denotes a zero-point synchronization signal circuit that generates a signal synchronized with the zero point of the AC power supply 11. The output of the rectifier circuit 13 for rectifying the AC power supply 11 is input to the inverter circuit 14. The inverter circuit 14 receives the output of the rectifier circuit 13 and drives the switching element to convert the output into an AC power supply having a predetermined frequency. Reference numeral 15 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 14. Reference numeral 16 denotes a D / A conversion circuit, which outputs an analog voltage to the voltage control oscillation circuit 15 in accordance with the data of the input digital signal. 17 is a reference power setting circuit,
A reference voltage corresponding to a constant value of the peak voltage applied to the switching element of the inverter circuit is set. 18
Is a switching element applied voltage detection circuit which detects the voltage applied to the switching element of the inverter circuit 14 and holds the peak value of the detected voltage. This value is the reference voltage set by the reference voltage setting circuit 17. Can be adjusted. Reference numeral 19 denotes a voltage comparison circuit, which outputs an output signal of the switching element applied voltage detection circuit 18 and a reference voltage setting circuit 1
7, and outputs the result of the comparison as an interrupt signal. Reference numeral 20 denotes a control circuit, which receives an output signal of the zero-point synchronization signal circuit 12 and an output signal of the voltage comparison circuit 19, and outputs the output signal of the voltage comparison circuit 19 at the timing of the output signal of the zero-point synchronization signal circuit 12. The digital signal data output to the D / A conversion circuit 16 is 1 LSB
And the control is performed such that the peak voltage applied to the switching element of the inverter circuit 14 is constant.

FIG. 2 is a circuit diagram of one embodiment of the present invention.
In FIG. 2, reference numeral 11 denotes an AC power supply, and 12 denotes a zero-point synchronization signal circuit which receives the AC power supply 11 and generates a signal synchronized with a zero point of the AC power supply 11. A rectifier circuit 13 rectifies the AC power supply 11. A capacitor 21 and a coil 22 are connected to the output of the rectifier circuit 13 and input to the inverter circuit 14. The capacitor 21 and the coil 22 prevent the noise generated in the inverter circuit 14 from affecting the AC power supply 11. The inverter circuit 14 includes a noise prevention capacitor 14a, a resonance capacitor 14b, a resonance coil 14c, and an IGBT 14 as a switching element.
d, protection diode 14e at the time of reverse voltage. Reference numeral 15 denotes a voltage-controlled oscillation circuit that changes the oscillation frequency of an output signal in accordance with the magnitude of the input voltage, and controls the switching element IG of the inverter circuit 14.
The BT 14d is driven. 16 is a D / A conversion circuit,
An analog voltage is output to the voltage controlled oscillation circuit 15 according to the data of the input digital signal. A reference voltage setting circuit 17 sets a reference voltage corresponding to a constant peak voltage applied to the IGBT 14d, which is a switching element of the inverter circuit 14. The reference voltage setting circuit 17 includes a resistor 17a, a diode 17b, a resistor 17c,
The reference voltage VC is composed of a resistor 17d, in which a resistor 17a and a diode 17b are connected in series, and a reference voltage VC divided by the resistor 17c is input to the + terminal of the voltage comparison circuit 19.
The diode 17b is a diode for temperature compensation. The resistor 17d is connected between the + terminal of the voltage comparison circuit 19 and the output terminal of the voltage comparison circuit 19 so that the reference voltage has a hysteresis characteristic. Reference numeral 18 denotes a switching element applied voltage detection circuit, which detects a voltage applied to the IGBT 14d, which is a switching element of the inverter circuit 14, by a resistor 1
8a and a resistor 18b, and further divides the voltage into a series resistor of a variable resistor 18c, a resistor 18d, and a resistor 18e.
The voltage is divided by the resistor 18f and the transistor 18
g, a resistor 18h, and a capacitor 18i. The output voltage VB of the peak hold circuit is input to the negative terminal of the voltage comparison circuit 19. Reference numeral 20 denotes a microcomputer which uses a DC power supply circuit 24 as a power supply,
The output signal of the voltage comparison circuit 19 is input, and based on the output signal of the voltage comparison circuit 19, the data of the digital signal to be output to the D / A conversion circuit 16 at the timing of the output signal of the zero point synchronizing signal circuit 12 in units of 1 LSB. Control. The capacitor 23 is connected to prevent noise from the AC power supply. The DC power supply 24 receives the AC power supply 11 and generates a stable DC power supply.

The operation of the above configuration will be described with reference to the flowchart of FIG. In step 30, as a load placed on the resonance coil 14c of the inverter circuit 14,
Consider a cooking pot. The power input to this pot is Pi
n, assuming that the set power to be input to the pan is Pw, and the power Pin input to the pan is different from the set power Pw, start the adjustment and proceed to step 31. In step 31, the power Pin input to the pan is set to the set power Pw
If greater, go to step 32. In step 32, the variable resistor 18c is adjusted to reduce the resistance value,
Step 34: The voltage VB across the capacitor 18i is increased so that the output of the voltage comparison circuit becomes low level.
Proceed to. Step 34 is processed by subroutine A. Conversely, in step 31, the power Pin input to the pan
Is smaller than the set power Pw, the routine proceeds to step 33. In step 33, the variable resistor 18c is adjusted to increase the resistance value, reduce the voltage VB across the capacitor 18i, and set the output of the voltage comparison circuit to a high level. Step 34 is processed by subroutine A. After step 34, step 3
Return to 0. In step 30, the power Pin input to the pan
And the same as the set power Pw, the process proceeds to step 35,
Adjustment of the variable resistor 18c is completed. From step 35,
Proceed to step 36. Step 36 is a subroutine A
And continue this. Next, the operation of the subroutine A will be described with reference to the flowchart of FIG. In step 40, the microcomputer 20 determines whether the voltage VB is higher than the voltage VC. That is, if the output of the voltage comparison circuit 19 is low, it is determined that VB is large, and if the output of the voltage comparison circuit 19 is high, it is determined that VB is small. In step 40, the voltage VB is equal to the voltage VC.
If it is larger, the process proceeds to step 41. In step 41, the output signal of the zero-point synchronization signal circuit 12 maintains the current state except for the zero point of the AC power supply 11,
When a signal indicating the zero point comes, the process proceeds to step 42. In step 42, the microcomputer 20 converts the digital signal data output to the D / A conversion circuit 16 into 1 LSB.
Then, go to step 43. In step 43, the data of the input digital signal is reduced by 1 LSB, so that the output voltage of the D / A conversion circuit 16 is reduced.
Next, the routine proceeds to step 44. In step 44, since the voltage input to the voltage controlled oscillation circuit 15 decreases, the voltage controlled oscillation circuit 15 increases the oscillation frequency by keeping the off time of the output signal constant and shortening the on time. That is, the ON time of the IGBT 14d is shortened,
The power input to the pot is reduced. Next, the routine proceeds to step 45. In step 45, in step 44, the IGBT1
Since the ON time of 4d is shortened, the IGBT 14
d decreases the peak voltage applied to the capacitor 1
8i also decreases. Conversely, if the voltage VB is smaller than the voltage VC in step 40,
Proceed to 6. In step 46, the output signal of the zero point synchronizing signal circuit 12 maintains the state up to now except for the zero point of the AC power supply 11, and when a signal indicating the zero point comes,
Proceed to step 47. In step 47, the microcomputer 20 changes the data of the digital signal output to the D / A conversion circuit 16 by +1 LSB, and proceeds to step 48. In step 48, the data of the input digital signal is increased by +1 LSB, so that the output voltage of the D / A conversion circuit 16 is increased. Next, the routine proceeds to step 49. In step 49, since the voltage input to the voltage controlled oscillation circuit 15 increases, the voltage controlled oscillation circuit 15
The oscillation frequency is lowered by keeping the off time of the output signal constant and lengthening the on time. That is, IGBT1
The on-time of 4d becomes longer, and the electric power input to the pan becomes larger. Next, the routine proceeds to step 50. In step 50,
In step 49, the peak voltage applied to the IGBT 14d increases because the ON time of the IGBT 14d increases, and the voltage VB across the capacitor 18i also increases. From step 45 and step 50 to step 5
Proceed to 1 and end subroutine A.

[0012]

More good urchin, according to the present invention, according to the present invention, Ru <br/> shall der to provide an inverter control circuit reliability improvement and cost.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of an inverter control circuit showing one embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of the inverter control circuit according to the embodiment of the present invention;

FIG. 4 is a flowchart showing an operation of the inverter control circuit according to the embodiment of the present invention;

FIG. 5 is a block diagram of a conventional inverter control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 AC power supply 12 Zero point synchronizing signal circuit 13 Rectifier circuit 14 Inverter circuit 15 Voltage control oscillation circuit 16 D / A conversion circuit 17 Reference voltage setting circuit 18 Switching element applied voltage detection circuit 19 Voltage comparison circuit 20 Microcomputer

──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Shinichi Sato 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-house (56) References JP-A 62-74783 (JP, U) JP-A 62-2181 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 6/12

Claims (1)

(57) [Claims] An inverter for supplying high frequency power from a commercial power supply.
And a switching element of the inverter circuit.
A voltage-controlled oscillation circuit to be driven;
A D / A conversion circuit for outputting an analog voltage;
And a control circuit that outputs a digital signal to the conversion circuit.
The control circuit is applied to the switching element.
According to the peak voltage of the commercial power supply,
Electromagnetic cooking by controlling the digital signal in 1LSB increments
Vessels of the inverter control circuit.