digitally controlled ckt breaker

Thread Starter


Joined Jun 24, 2011
Hi guys ,

My question is regarding a design for an electronically (digitally) controlled circuit breaker.

I have a pulse generator based on a high power pnp transistor whose source is connected to Vcc rail and its drain connected to the load. Once the base is driven low enough, the drain is "shorted" to the source and the output load sees a pulse.

The problem i would like to address occurs when the user shorts the output (he might not do it on purpose but the load is typically a solution with salts and due to electrochemical effects, some shorts might occur at times). I would like to protect my circuit from this situation, and also get some notification about this situation as it occurs.

A few constraints : the pulses i use are typically on the order of 100us.
the voltages were are talking about are 40v-200v dc. My loads could be on
the order of 10 ohm or so.

The solution i came up with until now, is have my own "sense" resistor - 1ohm which gets all the pulse if the user shorts the output. This way, i can stay within the current limitations of my transistor, but i lose some of the output voltage (which is important, i need as much of it as i can get).

I also thought about running the circuit through an external circuit breaker,but i am not sure what are the typical resistances of these devices, and also - they are mechanical, so i will have to manually bring them up when they trip - ideally i want an electronically controlled system, which detects a short (quickly - in less than 100us), and prevents damage before resuming normal operation.

Would appreciate design advice if you guys ran into similar issue.

Kind regards,

Ron H

Joined Apr 14, 2005
I don't see how 1 ohm will protect your circuit. If it gets the entire 200V, your switch draws 200A. Can it handle this? Can the 1 ohm resistor handle 40kW? I think we're missing something.


Joined Jun 7, 2009
if your fault condition is abnormal, than intervention should be required, ie; replacing a semiconductor fuse. If the 'fault' is not abnormal, then select devices that can withstand such short term values.