DESCRIPTION OF OPERATION
The Thyristor is triggered by deriving the gate current from the anode of the device, thus a small electrically-isolated control current initiates a large gate current without the need for a gate drive power supply. Upon application of the control current, the thyristor receives a fast-rising gate current which is fully maintained until the anode voltage of the thyristor collapses below the threshold voltage after it is triggered. This method of operation accounts for the low power dissipation of the trigger unit. Current flow is initiated by an opto-coupler which provides the electrical isolation. By maintaining the gate current long enough to reach the latching current the system can be safely used in applications with large inductive loads. The anode voltage of the thyristor must be at least 14V before the gate current reaches 200mA.
The full gate current is maintained until the when the anode voltage goes below 14V. The rise-time of the gate current is approximately proportional to the supply voltage and is typically 2A/µs. With the 12mA signal applied, there is a small turn-on delay of approximately 30µs and the full dv/dt can only be re-applied 100µs after removing the trigger signal from the control terminals. The turn-on delay tdi, can be reduced by pulse shaping because it is inversely proportional to the control current. The envelope of the voltage across the thyristor can have any desired shape provided the rms value is below Vm and the peak value does not exceed Vp.