Current limiter with PNP transistor

270

05:43:12

Used for limiting current output of positive voltage PSU. Very simple, two diodes in series provide fixed voltage difference for base-emitter diode and adjusting resistor. By lowering output load, current through adjusting resistor increases and when voltage on adjusting resistor and base-emitter equals voltage on diodes in series, current via adjusting resistor (÷output current) cannot increase anymore. With max. output current, voltage drop from PSU to output maybe asi high as 1 V, probably not suitable for low voltage PSU.

published 11 years ago

yashgumaste

11 years ago

You could add a switch at output which will demo a short circuit

Jizzer

11 years ago

Good idea, done. Thanks

JohnSmytheee

4 months ago

I know this is an old entry, and I kind of stumbled onto making this circuit mysel recently, and it seems to work well. One thing to note is you do need a well regulated voltage source to power it, or the current will not regulate well. The 19.4 ohm resistor seems to set the main current limiting, whereas the 33K resistor seems to set the "inflection point" of the divider that will bias the base on or off and keep your maximum current source to a fairly steady setpoint from your desired load to a low resistance fault / short. I like it because it is a true "High Side Source", which works better than a sink in some configurations where you cant split the low side to multiple current source return paths.

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.