KR0120227Y1 - Zero crossing control circuit for dielectric heating cooker - Google Patents

Abstract

The present invention relates to a dielectric heating cooker having a relay for controlling AC power supplied to both ends of a primary winding of a high voltage transformer for inducing high voltage for generating microwaves. The present invention is operated by a low voltage induced by a low voltage transformer and A driving instruction unit for generating a relay driving instruction signal indicating to drive the controller; a control unit for providing a relay driving unit with a control signal for driving the relay after a predetermined delay time has elapsed in response to the relay driving instruction signal; Detecting that the relay is 'ON' by the sensor to output a predetermined detection signal, and a timer for measuring the operation delay time of the relay from the moment the control unit outputs the control signal to the moment the monitoring signal is received from the detection unit Primary winding of the high voltage transformer It is characterized by an alternating current supplied to the stage so that the zero crossing is constituted by the delay time set to reset the delay time of the control.

Description

Zero-crossing control circuit of oil field heating cooker

1 is an overall circuit diagram of a dielectric heat cooker including the present invention.

2 is a flowchart illustrating a process of performing a function of a controller according to the present invention.

(A) to (d) of Figure 3 is a signal waveform diagram for explaining the operation of the present invention.

* Explanation of symbols for main parts of the drawings

10: control unit 11: timer

12: delay time setting unit 20: relay

30: driving instruction unit 40: relay driving unit

50: detection unit 61,62: constant voltage supply unit

The present invention relates to a cooker of a dielectric heating method using microwave electromagnetic energy, and in particular, an alternating current supplied to a transformer interrupted by a relay is zero-crossed. and a circuit for controlling the driving of the relay to be zero cross.

Dielectric heating type cooker is a cooker that applies the phenomenon that the frictional heat between molecules raises the temperature of the dielectric when the dielectric is placed on both ends of the alternating current. It is called a range and is a cooker equipped with a magnetron, which is a branching tube for generating microwaves having a frequency of about 2450 MHz.

In order for the magnetron to generate a high frequency of about 2450MHz, a high voltage of about 4000V is required. Such high voltage is provided from a high voltage transformer that boosts a normal voltage (110V or 220V).

The output control of the dielectric heating cooker is made by varying the supply cycle of the AC power provided to the primary winding of the high-voltage transformer, and is usually controlled by the interruption (ON / OFF) of a relay controlled by a microcomputer. The output is regulated.

As such, when a relay is used to interrupt an AC power supplied to an inductive load such as a transformer, a zero crossing of current does not occur at a moment when a contact of a relay is attached, so that a rush current flows into the transformer.

This inrush current instantly creates a large magnetic field, causing problems in the transformer, causing noise or unstable circuit operation.

In this way, the zero crossing of the current does not occur during operation of the relay, so that the inrush current induced by the transformer is the absolute value of the alternating current provided from the power supply to the transformer (current flow of about 15A to 20A in the case of a dielectric heating cooker). It has a maximum value when the relay is 'ON' in phase and has a minimum value when the relay is 'ON' in a phase where the absolute value of the AC current becomes minimum.

The minimum period of inrush current at 60Hz AC power is 1/120 seconds.

Accordingly, an object of the present invention is to provide a circuit for controlling the operation of the relay to minimize the generation of inrush current in the dielectric heating cooker interrupted by the relay.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 shows a circuit configuration of a dielectric heating cooker according to the present invention, wherein reference numeral 10 denotes a control unit realized by a microcomputer as a means for controlling the operation of various components, and reference numeral 20 denotes a microwave. A relay for interrupting the primary winding of a high voltage transformer (HVT) for inducing a high voltage to generate a voltage, and the reference numeral 30 is operated by a low voltage induced by a low voltage transformer (LVT) to A driving instruction unit for generating a predetermined driving instruction signal for instructing driving to the control unit 10, 40 is a relay driving unit controlled by the control unit 10 to drive the relay 20, and 50 is the relay 20 ) Detects 'ON' and provides a detection signal to the controller 10.

In addition, two constant voltage supply parts 61 and 62 are configured on the secondary side of the low voltage transformer LVT. The first constant voltage supply part 61 provides a DC voltage of 12V to the relay 20 and the second constant voltage supply part. 62 provides a DC voltage of 5V to the controller 10, the drive instruction unit 30, and the detector 50, respectively.

On the other hand, the control unit 10 according to the present invention is a relay driving unit 40 for driving the relay 20 after a predetermined internal delay time has elapsed in response to the relay driving command signal provided from the driving command unit 30. A timer for realizing a function of measuring the relay operation delay time from the moment of providing the control signal to the relay driver 40 and the moment of receiving the detection signal provided from the sensing unit 50 ( 11) and calculates an internal delay time such that the alternating current supplied to both ends of the primary winding of the high voltage transformer (HVT) makes a zero crossing when the relay 20 is 'ON' by the measured relay operation delay time. And a delay time setting section 12 for realizing the function of resetting as its own delay time.

Now, the operation of the present invention will be described in detail with reference to FIG. 2 showing the function performing process of the controller 10 and FIG. 3 showing the signal waveforms of the main components.

When the relay 20 is 'ON', power is supplied to the high voltage transformer (HVT) as shown in FIG. 3 (a). Since the transformer corresponds to an inductive load, the phase of the current is 90 ° behind the phase of the voltage. You lose.

The phase of the current and the voltage of the power source provided to the low voltage transformer LVT are also the same as in FIG.

The well-known driving signal generator 30 generates a square wave as shown in FIG. 3B as a driving instruction signal of the relay 30 when the voltage induced in the secondary winding of the low voltage transformer LVT has a positive value. To the control unit 10.

At this time, the controller 10 takes an interrupt at the falling edge of the square wave provided from the driving signal generator 30 and after the internal delay time T elapses, FIG. The same control pulse is provided as the base of the transistor TR1 in the relay driver 40 and the internal timer 11 is operated.

When the control unit 10 is provided (see (c) of FIG. 3), the transistor TR1 in the relay driver 40 is temporarily turned on so that the DC voltage from the first constant voltage supply unit 61 is relayed. Is supplied.

Therefore, a current flows through the movable coil of the relay 20 so that the movable contact of the relay 20 is connected to the fixed contact.

At this time, since the movable coil of the relay 20 is also an inductive load, after a predetermined delay time t has elapsed since the DC voltage is supplied from the first constant voltage supply unit 61 to the relay 20, the movable contact is connected to the fixed contact. Will blow.

That is, the relay 20 is in an 'ON' state after a predetermined time t has elapsed from the time when the voltage is supplied from the first constant voltage supply unit 61, and this operation delay time t is It depends on the type, and typical delay time of 7 ~ 9 mesc.

When the relay 20 is in an 'ON' state (i.e., when the movable contact is blown to the fixed contact), the photocoupler PC in the sensing unit 50 is activated to operate the low lever (or logical 0). The detection signal is provided to the controller 10. Therefore, the controller 10 measures the operation delay time t of the relay 20 through the timer 11.

Delay time setting unit 12 in the control unit 10 is the primary of the high-voltage transformer (HVT) during the operation of the relay 20 from the operation delay time (t) of the relay 20 measured by the timer 11 The delay time T1 for calculating zero crossing of the power current across the winding is calculated and reset as the internal delay time T.

Thereafter, the control unit 10 responds to the relay driving command signal provided from the driving command unit 30, and then after the internal delay time T1 newly set by the delay time setting unit 12 elapses, By generating a control pulse for controlling the operation (see (c) of FIG. 3), the moment when the movable contact of the relay 20 is attached to the fixed contact point and the time when the power current value becomes 0V are first, As described above, zero crossings of the power current are made at both ends of the high voltage transformer HVT.

According to the present invention as described above, since the zero crossing of the current in the transformer is accurately made by the operation control of the relay, it is possible to prevent the inrush current and the generation of noise due to this.

Therefore, the present invention can be applied to any device that requires a relay and minimizes inrush current.

Claims (1)

A relay for intermitting (ON / OFF) the AC power supplied to the primary winding of the first transformer for inducing high voltage for generating microwaves, and a low voltage induced by the second transformer to drive the relay. Means for generating a drive instruction signal, said control means being provided to the relay drive means for a control signal for driving said relay after a predetermined delay time T has elapsed in response to said drive instruction signal. In the heating cooker, sensing means for detecting that the relay is 'on' by the relay drive signal to output a predetermined detection signal, and from the detection means from the moment the control means outputs the control signal Timer means for measuring a relay operation delay time (t) up to the moment when a detection signal is provided; Dielectric heating including delay time setting means for resetting the delay time T of the control means such that an alternating current supplied across the primary winding of the first transformer is zero crossed by an operation delay time t. Cooker current zero crossing control circuit.