How to Discharge a Capacitor Into a Coil Using SCR Without Latching From Charging Path?

The discussion addresses the challenge of discharging a large electrolytic capacitor (10,000 µF) into a small coil using an SCR (Silicon Controlled Rectifier) as a switch without the SCR latching due to current from the charging path. The original circuit uses a resistor (R1) to limit charging current; however, lowering R1 to speed capacitor charging causes the SCR to remain latched because of holding current from the supply. The goal is to isolate the capacitor charging path from the SCR and coil discharge path without adding complex switching elements. Suggestions include using a small pass transistor to interrupt the charging supply during SCR conduction, employing low-voltage AC with a diode to create pulsed DC for capacitor charging, and adjusting gate-to-cathode resistor values to modify SCR holding current. Alternative solutions proposed are using a larger SCR with higher holding current or replacing the SCR with a transistor or MOSFET for better control and simpler switching. A more complex transistor arrangement was suggested to isolate the capacitor and SCR during discharge, but this increases circuit complexity. The consensus leans toward using a MOSFET switch due to its ruggedness and ease of control, especially given the large capacitor size and energy involved. Reference is made to R.M. Marston's "110 Thyristor Projects" as a useful resource for SCR applications. Proper trigger pulse amplitude and duration are emphasized for reliable switching, particularly with MOSFETs. The discussion also touches on practical considerations such as protecting FETs from damage during assembly and the importance of grounding.
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