Published:2009/7/8 22:13:00 Author:May | From:SeekIC
A basic circuit to trigger an SCR is shown in Fig. 67-1A. This circuit has the disadvantage that the blocking voltage of the photoncoupler output device determines the circuit-blocking voltage, irrespective of higher main SCR capability.
Adding capacitor C1 to the circuit, as shown in Fig. 67-1B, will reduce the dV/dt seen by the photon-coupler output device. The energy stored in C1, when discharged into the gate of SCR1, will improve the di/dt capability of the main SCR.
Using a separate power supply for the coupler adds flexibility to the trigger circuit; it removes the limitation of the blocking voltage capability of the photon-coupler output device. The flexibility adds cost and more than one power supply nftght be necessary for multiple SCRs if no common reference points are available.
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