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Re: nice polyfuse

The series power resistor idea is interesting. Are you wanting to put the PTC in a circuit with voltage above its rating ?

If 1 Ohm 5 watts limits the voltage across the PTC then it's probably good.

0.07 Ohms, cold, is good.

We use a 250V 1/2 amp PTC as well as the 1206 size ones.

One problem we had with a 1206 15V PTC was that sometimes (rarely) it would burn through and short to the next layer down which was 5V. A thicker PCB should fix that as well as getting rid of copper just below the PTC on the next layer down.

boB

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boB
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One approach is to increase the thermal coupling between the resistor and the polyswitch.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

SW protection is nice, but what happens during power up or when the customer only applies power to the relay section, not the unit power. Then there's no protection.

What do you need the series resistor for, maybe I missed the point?

Looks nice. Now I have to buy one, hoarding instruments you know.

I have a lot of Siglent stuff.

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Good instruments, but horrible PC software.

Reply to
Klaus Vestergaard Kragelund

I was thinking, that you could do a solid state switch with current sensing for each wire, but that would probably be a nightmare in time and parts.

A PTC should work, if you have a trace which is a couple of mm wide, it can handle more than 10A at 60degrees delta. So you should be able to find a PTC that will protect the trace (I am guessing this is low voltage DC)

Reply to
Klaus Vestergaard Kragelund

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