Thanks very much for the replies.
I have looked up Crowbar Circuits and found this example:
Practical Electronics/Crowbar circuit - Wikibooks, collection of open-content textbooks
- If I want to 'allow' up to 4.0A current, then would I replace the 250mA fuse in that example for a 4.0A fuse?
- It looks to me like I should use a 6V Zener (ZD1) to protect a circuit and supply that is rated at 5V. Is that correct?
- Can anyone help me understand how to select values for the Thyristor or Schottky diodes - Q1 and SD1?
If anyone has links to other clearer explanations of how Crowbar Circuits work, then I'd be very grateful - I'm still not completely clear on it.