JPH0321193Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a thyristor ignition control device used in a resistance welding machine, etc., and particularly to an ignition control device using a timer IC to obtain an ignition signal in the positive and negative half cycles of alternating current. .

A conventional thyristor firing control device using a timer IC is shown in FIG.

In the figure, 1 is a timer IC (hereinafter referred to as a sequential timer circuit), which has a trigger terminal.
TR, reset terminal RS, control voltage terminal
It has CV, threshold voltage terminal TH, discharge terminal D, power supply terminal V ₊ , earth terminal GND, and output terminal OUT. The internal circuit of this is as shown in Figure 2, comparators 2 and 3, reset flip-flop 4, and discharge
It consists of FET 5, voltage dividing resistors 6, 7, 8, etc., and when the reset signal input to the RS terminal becomes high level, it receives a trigger signal, and when the trigger signal input to the TR terminal becomes low level, comparator 2 is activated. As a result, the flip-flop 4 is set, and the output signal from the OUT terminal rises to a high level. From then on, the output signal is maintained at a high level until the threshold voltage entering the TH terminal increases gradually and reaches the reference voltage (control voltage) set at the CV terminal. When the threshold voltage reaches the reference voltage, the output signal of comparator 3 Upon activation, flip-flop 4 is inverted and reset. As a result, the output signal falls to a low level, and at the same time, the discharge FET 5 is turned on to return the threshold voltage to OV.

In Figure 1, this sequential timer circuit 1
An integral capacitor 9 for supplying a threshold voltage, a volume resistor 10 for current adjustment, a volume resistor 11 for minimum current adjustment, a volume resistor 12 for standard voltage adjustment, a discharge resistor 13, and a differentiator circuit 14 are externally connected to the differentiater circuit 14. An ignition control device is constructed by connecting the output end of the ignition control device to the primary side of the pulse transformer 15.The energizing signal of the resistance welding machine is added as a reset signal, and a signal synchronized with the zero-crossing point of the AC power supply voltage is used as a trigger signal. The differential waveform at the fall of the output signal obtained from the OUT terminal when the signal is applied is taken out as ignition signals A and B by the pulse transformer 15, and this ignition signal is used to reverse the output signal to the primary side of the welding transformer 16 in the main circuit of the resistance welding machine. The thyristors 17A and 17B connected in parallel are alternately fired in positive and negative half cycles of the power supply voltage to energize the load. The level of the ignition signal is thyristor 17A, 1
If the signal is not sufficient for ignition of 7B, an auxiliary thyristor or the like may be used to amplify the signal. FIG. 3 shows voltage waveforms at various parts during normal operation.

In such a conventional thyristor firing control device, since both the reference voltage (control voltage) and the time constant of the threshold voltage are variable, the time T until the threshold voltage reaches the reference voltage can be adjusted. However, due to an incorrect adjustment or an abnormal rise in the power supply voltage V ₊ , the reference voltage may become too high.
If the time constant of the threshold voltage is too long,
As shown in FIG. 4, there are cases where the intersection of the threshold voltage and the reference voltage does not fall within a half cycle, and as a result, there is only one firing signal per cycle, and the thyristors 17A and 17B are fired on one side (the fourth In the example shown in the figure, only the negative half cycle is fired), resulting in biased magnetization of the welding transformer 16 and thyristors 17A and 1.
There was a risk that 7B would be destroyed.

An object of the present invention is to provide a thyristor ignition control device that eliminates the above-described drawbacks of the prior art and has improved reliability.

In order to achieve the above object, the present invention synchronizes the reference voltage (control voltage) of the sequential timer circuit with the AC power supply voltage and forcibly lowers it to OV once every half cycle, thereby reducing the difference between the threshold voltage and the reference voltage. The intersection point is always placed within a half cycle.

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 5 is a diagram showing one embodiment of the present invention, and the basic configuration of the ignition control circuit that uses a sequential timer circuit to generate an ignition signal is the same as Fig. 1, so the parts corresponding to Fig. 1 are shown. are given the same reference numerals and their explanations will be omitted.

Reference numeral 18 denotes a synchronous circuit provided to prevent single firing, and is constructed as follows. That is,
The AC power supply voltage stepped down by the control transformer 19 is full-wave rectified by the diode stack 20, and the part of the rectified waveform that exceeds a certain voltage is cut by the Zener diode 21 and sent to the plus side input (# ₁ ) of the operational amplifier 22.
Put it in. On the other hand, the DC voltage V ₊ is applied to the negative input (# ₂ ) of the operational amplifier 22 through resistors 23, 24, 2.
5 is input, and a square wave that falls to a low level (OV) just before the zero-crossing point of the AC power supply voltage and rises to a high level after passing the zero-crossing point is output to the output ( _# 3) of the operational amplifier 22. generate.

The output terminal of the operational amplifier 22 is connected to the cathode of the diode 26, and the anode of the diode 26 is the reference voltage point of the sequential timer circuit 1.
Connect to the CV terminal so that the output of the operational amplifier 22 is
The diode 26 is made conductive only when the voltage becomes OV.

In this way, as shown in the waveform diagram of FIG. 6, the output of the operational amplifier 22 is compared with the threshold voltage of the sequential timer circuit 1 once every half cycle, that is, immediately before the zero-crossing point of the AC power supply voltage. Reference voltage (control voltage)
Since is pulled down to OV, the threshold voltage always reaches the reference voltage within half a cycle, at which time comparator 3 shown in FIG. 2 operates to reset flip-flop 4. Therefore, the ignition signal is reliably generated every half cycle, and there is no single ignition as in the prior art.

The diode 26 is provided so as not to affect the reference voltage except when the output of the operational amplifier 22 becomes OV, and other elements may be used as long as they have the same function.

As explained above, according to the present invention, when a sequential timer circuit is used to generate an ignition signal, even if there is an abnormal rise in the power supply voltage or an adjustment error, the ignition signal is always generated within a half cycle. The welding transformer becomes polarized due to single ignition, and as a result, accidents such as a large current flowing through the primary side and destruction of the thyristor can be prevented.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a thyristor firing control device using a conventional sequential timer circuit, Figure 2 is an internal circuit diagram of the sequential timer circuit, Figure 3 is a voltage waveform diagram of each part during normal operation, and FIG. 4 is a diagram of voltage waveforms at various parts when single firing occurs, FIG. 5 is a circuit diagram showing an embodiment of the present invention, and FIG. 6 is a diagram of voltage waveforms at various parts thereof. 1...Sequential timer circuit, TR...Trigger terminal, RS...Reset terminal, CV...Control voltage terminal (reference voltage point), TH...Threshold voltage terminal, D...Discharge terminal,
OUT... Output terminal, 9... Integrating capacitor, 1
4...Differential circuit, 15...Pulse transformer, 18
...Synchronous circuit, 26...diode.

Claims (1)

[Claims for Utility Model Registration] A thyristor ignition control device that alternately controls ignition of a thyristor connected in antiparallel to a welding transformer in positive and negative half cycles of an AC power supply voltage that is synchronized with an AC power supply connected to the thyristor. When a trigger signal synchronized with the zero-crossing point of the AC power supply voltage is input to the trigger terminal, the output signal rises to a high level, and then the input voltage to the threshold voltage terminal, which gradually increases with a predetermined time constant, is input to the control voltage terminal. When the predetermined reference voltage is reached,
It has a sequential timer circuit in which the above output signal falls to a low level, and a differential waveform at the fall of the above output signal is applied to the primary side of the pulse transformer, and multiple ignition signals are generated on the secondary side of this pulse transformer. In the thyristor ignition control device that alternately fires the thyristor in the positive and negative half cycles of the AC power supply voltage, a full-wave rectifier circuit that full-wave rectifies the AC power supply voltage, and an output terminal of the full-wave rectifier circuit. A synchronous circuit includes Zener diodes connected in parallel and an operational amplifier that generates a square wave signal by comparing the voltage from the Zener diodes with a predetermined comparison voltage, and an output signal of the synchronous circuit becomes low level. 1. A thyristor ignition control device comprising a diode having one cathode connected to the output terminal of the synchronous circuit and the other anode connected to the control voltage terminal so as to be conductive only when the thyristor ignition control device is turned on.