Operational Characteristics of a SCR-based Pulse Generating Circuit

LCDR Christopher Chang, Singapore Navy

A commercial off-the-shelf silicon controlled rectifier (SCR) was connected in series with a parallel RC load under DC bias to produce self-terminating pulses. The physics underlying the switching mechanism of the SCR in such circuit was investigated and the values of load resistance and capacitance varied to ascertain their role on the pulse generating capability of the circuit. When pulsing was successfully achieved, a reverse recovery current was always present to return the SCR from its “on” state to its “off” state. In addition, the regenerative process by which charges were avalanched into the circuit each time the SCR was turned on appeared to be independent of the mode of triggering, either by increasing DC bias or using a current at the gate. Significantly, pulsing was discovered to be sustainable for a specific range of RC values that depends on the SCR’s intrinsic turn-off time. Specifically, it was found that without making modifications to the SCR itself, the minimum dead time achievable between pulses was essentially the turn-off time of the SCR. The findings of the research will help to design optimum SCR based circuits for pulse mode detection of light and ionizing radiation without external amplification circuitry.

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Jan 04, 2015

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