Squib-firing circuit 2
Posted on May 2, 2012 8676
The LRC input network limits the anode dv/dt to a safe valueâ€”below 30 V/jus. Rl provides critical damping to prevent voltage overshoot. While a simple RC filter section could be used, the high current required by the squib would dictate a small value of resistance and a much larger capacitor. Resistor R3 provides dc bias stabilization, while C3 provides stiff gate bias during the transient interval when anode voltage is applied. The SCR is fired one second after arming by means of the simple R2C2Z1 time delay network.
R4 provides a load for the SCR for testing the circuit with the squib disconnectedâ€”limiting the current to a level well within the continuous rating of the SCR. The circuit can be reset by opening the +28 V supply and then re-arming.