Hey guys,
So I have a small PCB mount DC-DC converter, which takes any DC input from 18-30V DC and converts it into 5V, with a max output of 300mA. It's a pretty neat device, but it has no over-voltage handling. I'm planning to add a resettable fuse for over-current protection, but I also would like the fuse to blow when there is over-voltage (from environmental factors, or from user errors of inputting >30V DC).
I've read quite a bit online about over-voltage protection and it seems the common thing to do is build a crowbar circuit.
I'm a little confused as to why I can't just put a fuse in series with the source, and then a zener diode to ground? For example, use a 250mA fuse and a 33V zener diode? Under normal voltages, the diode will act as a normal diode and block current flow to ground. When the voltage reaches 33V, the diode will act as a short circuit. There will be a voltage drop of 33V over a tiny resistance, which will probably blow the fuse immediately. I assume the problem would be finding a zener diode which can withstand this high current surge. I know that some zener diodes have very high surge current ratings though. Will it work with just a zener diode and fuse? I may be misunderstanding something and I hope someone can help clear it up.
Thanks.
So I have a small PCB mount DC-DC converter, which takes any DC input from 18-30V DC and converts it into 5V, with a max output of 300mA. It's a pretty neat device, but it has no over-voltage handling. I'm planning to add a resettable fuse for over-current protection, but I also would like the fuse to blow when there is over-voltage (from environmental factors, or from user errors of inputting >30V DC).
I've read quite a bit online about over-voltage protection and it seems the common thing to do is build a crowbar circuit.
I'm a little confused as to why I can't just put a fuse in series with the source, and then a zener diode to ground? For example, use a 250mA fuse and a 33V zener diode? Under normal voltages, the diode will act as a normal diode and block current flow to ground. When the voltage reaches 33V, the diode will act as a short circuit. There will be a voltage drop of 33V over a tiny resistance, which will probably blow the fuse immediately. I assume the problem would be finding a zener diode which can withstand this high current surge. I know that some zener diodes have very high surge current ratings though. Will it work with just a zener diode and fuse? I may be misunderstanding something and I hope someone can help clear it up.
Thanks.