Posted on Jun 13, 2012 7052
The adjustable circuit breaker responds in 0.02 sunder all conditions-provided you select a fast relay for Kl. For moderate overload conditions, it`s preferable to use the fuse or the fast-acting breaker. Toroid transformer Tl senses ac load current and produces an ac signal at the wiper of Rl, when switch S3 is closed. Diode Dl rectifies this signal to produce a positive voltage at test point TPl. Because Rl allows you to calibrate this voltage, the circuit accommodates a variety of current-sense transformers.
To calibrate the trip threshold, apply the maximum expected overload and adjust Rl until the TPl voltage is 0. 7 V below the positive saturation level for ICl. Then adjust R4 for the desired trip point. To reset the circuit breaker after it has tripped, open Sl or S2.