Right, I have a I/O that needs to source 1.5A but be clamped at 5v as the external device it's conected to can have between 5-24v and itself can source 15A
Please help!!!
Steve
P.S. just re-looked at resistor and know I think even the 15ohm is too large!! should be 3ohm if it's 5v to be able to supply 1.5A, I'm getting confused
This is the voltage limiting bit I have cobbled to the circuit board. Am I on right lines thinking it's the low value resistor causing the diode to pop and that if I want to source 1.5A I need to either up the wattage of the diode or create the shunt power transistor you suggest?
P.S. Ignore the part number on the circuit it is a BZX84-C5V1 I'm using
I can only think it's the low value resistor allowing too much current to flow but I need this to be low to allow me to source 1.5A. the only other way (if I'm on right track) is to have a > 33.75w diode!
I have made a test probe for serial communications this test probe can monitor AND inject data to a USART line at 5v, it injects commands by forcing the line high (max 1.5A) and pulling it low as it requires to send the command, this ensures the command issued is not overridden by another device talking over it. However normally it sits and listens. It is connected using bipolar transistors so as not to intefere until we need to.
Whilst roaming around a board testing it, I sometimes hit a higher voltage line (24v max) by accident these lines and can supply many amps.
I know, I know, "be more carfull" but it happens and it blows a component, whilst this does not happen every day when it does it's a pain so I want to clamp this line to +5v somehow.
Hi Ericgibbs (and anyone else that may be able to answer this)
Eric, I didn't understand what you meant by "Its possible to use a standard zener to drive the base of a shunt power transistor" but I went looking and I found out what you meant it's called a 'amplified zener shunt stabilizer'
I think this will work great but I have one question why do we still need the resistor if the transistor now regulates the current stopping it blowing the zener?