2N2646 based Voltage controlled SCR Pulser

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A Center tap 50Hz Step Down Transformer with two diodes is used to get a train of Positive Sine Pulses at 100Hz which is applied to Q6 base via R51.

2N2646 is a unijunction transistor(UJT) in a TO-18 metal package. The control voltage or voltage proportional to error is fed to R56-Q3, The UJT drives a pulse transformer which provides isolation from the Load which the SCR bridge is controlling.

This phase angle control gives a near Linear closed loop control for a SCR bridge which may be used in Electroplating or a Preregulator of a big power supply.

High Energy Circuits

MOSFET and IGBT based systems are now more in use than Thyristor – Triac – SCR based designs in power electronics. Thyristors are more robust than many power devices.

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