JPS5842952B2 - Soft start circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a soft start circuit that uses Cyrisk to gradually shift the control phase of a circuit for controlling the phase of an electric furnace, etc. when starting the power supply and when there is a sudden change in the input signal. .

Molybdenum silicide (MoS l 2 )-based heating elements, which are generally used as heating elements in electric furnaces, have a specific resistance (, R-CrrL) vs. temperature (°C) graph in Figure 2, which shows the ratio at low temperatures. Since the resistance is very small, if an excessive voltage is applied when starting up the electric furnace, a current ten times higher than the steady operating current will flow through the heating element, causing deterioration of the heating element and causing damage to the heating element. There is a risk of destroying the controlled Cyrisk element.

Furthermore, since the furnace is at a low temperature when the power supply is started in a furnace using feedback control, the feedback signal will show the maximum value. be.

To protect these heating elements and cyrisk elements,
A soft-start circuit is used that gradually shifts the control phase of the thyrisk element when starting the power supply, but conventional soft-start circuits do not handle the sudden change in input signal that occurs when the temperature control is suddenly changed during operation. There is a problem that the soft start function does not operate in response to large fluctuations, and there is also a problem that the soft start function has an adverse effect on responsiveness during normal control.

The present invention has been made in view of the above points, and provides a soft start function even in response to sudden fluctuations in the input signal that occur when the temperature control of the temperature controller is suddenly changed.
Another object of the present invention is to provide a soft start circuit which does not have any influence on the control during normal control and is free from the risk of deterioration in responsiveness.

The illustrated embodiment in which the circuit according to the present invention is applied to feedback control of an electric furnace will be described below.

In the figure, reference numeral 1 denotes an electric furnace, and inside the electric furnace 1 there are installed a molybdenum silicide heating element 2 having a temperature-resistivity characteristic shown in FIG. 2, and a temperature detector 3 made of a thermoelectric element or the like.

The heating element 2 is connected to a power source 5 via a sirisk circuit 4 installed outside the furnace, and the detection signal from the temperature detector 3 is sent via a temperature controller 6 to a pulse generator having a soft start circuit. 7 is input.

Further, a synchronizing signal from the power source 5 is input to this pulse generator 7 via a synchronizing circuit 8, and a trigger pulse generated by the pulse generator 7 is input to the thyrisk circuit 4.

The pulse generator 7 has a circuit configuration as shown in FIG. terminal, 12 is an amplifier that amplifies the input signal, P
is PUT, L is relay 13, normally closed contact of the relay, Tr
is a transistor, R is a resistor, C is a capacitor, D is a diode that short-circuits the induced current of the coil, 14.15 is a power synchronization terminal connected to the synchronous circuit 8, 16 and 17 are PU
The output terminal from T is connected to the gate of the SIRISC circuit via a pulse transformer or the like.

To explain the operation of this circuit, first, when +Vcc is applied to the terminal 9, the transistor Tr1 is normally OFF.
Since the transistor Tr2 is in the FF state, a current flows through the base of the transistor Tr2 through the resistor R1.
2 is in the ON state.

Therefore, since current is flowing through the relay L via the resistor R2, the normally closed contact 13 of the relay L is open, and the capacitor C1 is sufficiently charged via the resistors R3 and R4. There is.

Since the base voltage of the transistor Tr3 is increased to the saturation region by this capacitor C1, the transistor Tr3 is turned on, and a sufficient current flows through the base of the transistor Tr4 controlled by this transistor Tr3. Therefore, the transistor T r 4 is in the ON state.

Therefore, the input amplified by the amplifier 12 is the transistor Tr.
4 and the time constant circuit's resistors R6 and R7, the capacitor C2 is charged, and the potential at point A, which is raised by charging the capacitor C2, that is, the anode potential of PUT, is divided by the resistors R8 and R9. When the potential at point G exceeds the gate potential of the PUT, the anode and cathode of the PUT are turned on, and the charge stored in the capacitor C2 is discharged through the resistor R1o. A potential is generated at both ends.

At this time of discharge, the charge in the capacitor C2 has not yet been completely discharged, so the PUT remains ON, and this state continues until the charge in the capacitor C2 is completely discharged by the power synchronization circuit 8, which will be described later. There is.

However, a signal from a power synchronization circuit is applied between the resistors R6 and R7, and this synchronization circuit 8 includes a bridge 18 for full-wave rectification of the alternating current of the power supply 5, as shown in FIG.
Resistor R111R12 that divides this full-wave rectified waveform
1R13 and two transistors Tr5+Tr6, and the transistor Tr5 is set to be turned ON above the vB point of the rectified waveform W1 shown in the waveform chart I of FIG.

Therefore, this transistor Tr5 is in the OFF state below the vB point, that is, near the zero potential of the waveform, and this transistor T
When the transistor Tr5 is in the OFF state, a current is applied to the transistor Tr6 controlled by the transistor r5 through the resistor R14, so that the transistor Tr6 is turned on.

The emitter terminal and collector terminal of this transistor Tr6 are connected to the power supply synchronizing terminals 14 and 15 of the pulse generator 7, respectively, so that the ON state of the transistor Tr6,
That is, near the zero potential of the power supply waveform, the charge in the capacitor C2 is completely discharged via the resistor R7.

This causes the capacitor C2 to lose its charge and is charged again through the transistor Tr5 and resistor R6°R7.
By repeating the above, continuous pulse waves W2 are obtained from the output terminals 16 and 17.

In addition, since charging of capacitor C2 is always performed starting from the point in time when the power supply waveform passes near zero potential, output terminal 1
The pulse wave W2 obtained from 6.17 is synchronized with the AC waveform of the power source 5.

To briefly explain the above operation using the waveform diagram I-V in FIG.
Charging of the capacitor C2 starts from point 1, and since the transistor T r 4 is in a low resistance state, the potential at the point A is as shown in the waveform diagram.
The battery is charged by drawing an inclination angle with a time constant T1 of 7.

As this charging progresses, at a point t2 where vA exceeds the VG point, the capacitor C1 is discharged by the PUT, and the potential at point A drops rapidly, and further reaches the conduction range t1 of the transistor Tr6, where it is completely discharged and the charge becomes zero. state, and charging is repeated again from this point.

Due to the discharge current at t1 mentioned above, a pulse wave W2 shown in the waveform diagram ■ is obtained between the output terminals 16 and 17, and this pulse wave W2 triggers the gate of the thyrisk circuit and the pulse wave W2 shown in the waveform diagram ■
The current W3 to the furnace 1 is controlled as shown in FIG.

Next, to explain the operation when the power is turned on from a state where the power is turned off, the normally closed contact 13 of the relay L is closed when the power is turned off, so the capacitor C1 is connected via the resistor R15. is in a short-circuited state.
When the power is turned on, the normally closed contact 13 is opened by the relay L, and the capacitor C1 and the resistor R3 are connected to the capacitor C1.
It is charged with a time constant of .

Since this charging starts with the capacitor C1 completely discharged, the capacitor C1 does not have the voltage to turn on the transistor Tr3 at the beginning of the charging (here, the transistor Tr3 is in an OFF state).

Therefore, since the emitter-collector of the transistor Tr4 controlled by the transistor Tr3 is in a high resistance state, the input from the amplifier 12 is hardly charged into the capacitor C2, and the small amount of charge that is charged operates the PUT. There is no pulse output since the discharge is previously caused by the synchronization signal, and therefore no current flows in the heating element 2 of the furnace 1.

Furthermore, the charging of the capacitor C1 progresses, and the transistor T
When the base voltage of r3 increases and the transistor Tr3 advances to the active region, a collector current according to the base voltage flows, and as a result, the base current of the transistor Tr4 flows, so that the emitter-collector resistance of the transistor Tr4 decreases. The capacitor C2 is charged with a time constant T2 including the resistance value of the transistor Tr4.

The time t3 at which the potential vA at point A reaches point vG due to this charging is determined by the time constant T2, as shown in the waveform diagram ■ in FIG.

Since this time constant T2 includes the resistance valve of the transistor Tr4, it is larger than the time constant T1 when the transistor Tr4 is completely conductive, and is delayed by a time proportional to the time constant. The pulse wave W2 is then oscillated.

Furthermore, as the capacitor C1 is charged, the resistance value of the transistor Tr4 decreases, so the pulse generation time advances, and when the capacitor C1 is finally fully charged, the transistor Tr4 becomes completely conductive, as described above. Oscillation is performed with a constant time constant T1 due to the state, that is, resistors R6 and R7, and thereafter the oscillation time is determined depending on the magnitude of the input signal.

Next, a description will be given of the circuit operation when the temperature adjustment of the temperature controller 6 is suddenly changed.

When a step-like input is applied to the input signal terminal 10.11 by changing the adjusted temperature, a trigger pulse corresponding to the step is generated by a differentiating circuit including a capacitor C3 and a resistor R16.

This trigger pulse is applied to the transistor T via the resistor R1□.
This pulse instantly turns on the transistor Tr1.

When this transistor Tr1 is in the ON state, the transistor Tr2 is in the OFF state, so the normally closed contact 13 of the relay L
is momentarily closed and the charge on capacitor C0 is transferred to resistor R1.
5.

The circuit operation after the capacitor C1 is discharged in this way is similar to the operation that occurs when the power is turned on from the power-off state.

In this embodiment, a relay L is used as a method of discharging the charge of the capacitor C1, but the circuit may be configured using a switching element such as a FET1 transistor.

As explained above, according to the present invention, there is provided a differentiating circuit that detects a sudden change in an input signal, a capacitor that is short-circuited via a relay by the output of the differentiating circuit, and a resistance value that changes as the voltage of the capacitor increases. A transistor is installed that is set so that the temperature gradually decreases, and this transistor is used as a resistor in a time constant circuit that determines the phase of the trigger pulse that activates the thyristor, so the temperature control of the controller can be changed. Even when the input signal suddenly fluctuates, such as during operation, the soft start function works, and has the effect of preventing deterioration of the heating element and destruction of the Cyrisk element.

In addition, its soft start function does not affect the control during normal control, that is, when the phase is controlled according to the magnitude of the input signal, and there is no risk of deterioration in response. effective.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a control system of a furnace equipped with a circuit according to the present invention, Fig. 2 is a graph showing the temperature-specific resistance characteristics of a heating element used in the furnace, and Fig. 3 is a diagram showing the control system of a furnace equipped with a circuit according to the present invention. A circuit diagram of a pulse generator having a soft start circuit according to the above, and FIG. 5 is a waveform diagram. 7... Pulse generator, Figure 4 is a synchronous circuit diagram, 10.11... Input signal terminal, R... Resistor, C... Capacitor, Tr... ...transistor.

Claims (1)

[Claims] 1 The cyrisk connected between the AC power source and the furnace heater,
A soft start circuit used in a pulse generator that performs ON-OFF operation based on the synchronization signal from the AC power supply and the furnace temperature detection signal, and when a step input signal is applied to the input signal terminals 10 and 11. Differentiating circuits C3 and R16 that generate trigger pulses, a relay L that is turned on and off by the output of the differentiating circuit, and this relay L.
The capacitor C1 is short-circuited by the capacitor C1, and the time constant circuit R6, R7, C2 that determines the phase of the trigger pulse that activates the cyrisk is connected between the input terminal 10°11, and as the voltage of the capacitor C1 increases, , and a transistor Tr4 whose resistance value is set to gradually decrease.