Silicon-controlled-switch — Saturable-transformer current limit

THE INCREASING use of semiconductors in power circuits requires fast-responding and accurate current-limit circuits (CLs) with high efficiency and with a control circuit insulated from the power circuits. Inverter, converter, time-ratio-control (TRC), and power-switching circuits need CLs that can turn off the power semiconductor within a few microseconds (μsec) after over current occurs. The desire for small overload in semiconductors necessitates accurate CLs (1% to 5%). The current-sensing device should require very little expenditure of power; therefore, the power-wasting current-measuring shunts ought to be avoided.