Hi,
What if to use these PTCs instead of traditional fuses in amp power rails, but use these thermally coupled to ensure they're share the same temp and will open together at once. To be sure they specs are close enough to act simultaneously, cutting both rails at once, it could be possible to match every pair using powerful lab power supply to measure current pass ability of each one before they'll open and make a pairs based on these results.
There are not much high voltage high current ones available on the market, but there are some that could be used in up to 100W class AB amps I suggest. There are numbers of PTCs offering quite low initial resistance, but I don't know how far it will rise in case of significant current will flow.
I suggest also matched ones possibly could be used as pairs in each of power rail to double max current or to cut resistance.
What you think?
What if to use these PTCs instead of traditional fuses in amp power rails, but use these thermally coupled to ensure they're share the same temp and will open together at once. To be sure they specs are close enough to act simultaneously, cutting both rails at once, it could be possible to match every pair using powerful lab power supply to measure current pass ability of each one before they'll open and make a pairs based on these results.
There are not much high voltage high current ones available on the market, but there are some that could be used in up to 100W class AB amps I suggest. There are numbers of PTCs offering quite low initial resistance, but I don't know how far it will rise in case of significant current will flow.
I suggest also matched ones possibly could be used as pairs in each of power rail to double max current or to cut resistance.
What you think?
That is what I would also answer.
They are good if:
Automatic reset is required.
You can afford the V drop.
You don't need fast protection.
They are rated for the voltage that they see when open. (I not only let the smoke out once but some internal bits as well)
If you have a fault, or even a bass note of low enough frequency, the two rails will not have equal current and will not open simultaneously. It depends on your amplifier topology as if this is important or not, but the hypothesis of both acting simultaneously is false.
To be on the safe side, I'll be the third no.
To be on the safe side, I'll be the third no.
Thanks for the input guys, that was just a theory that have to be checked. I've found this paper http://old.iihr.uiowa.edu/~hml/people/kruger/Publications/ChipCenter/pptc01.pdf there is mentioned that there are some of PPTC with a fast reaction time of a few milliseconds, but I haven't found these yet, would be cool to check them in practice if these are exist.
I found such type fuses are been used in amps. I remember some time ago I had a commercial integrated amp Atoll IN50, which had a resettable fuse in it, after pushing it hard for some time it cuts the output and then reset after a several seconds of cooling if turn the volume down. Don't remember where it was located, at the speaker output or at trafo's primary, but if I can remember it was rated 3A, so mostly like to be in the OP as it has 160VA 2x30 or 2x35v trafo which is far lower consumption for that.
I found such type fuses are been used in amps. I remember some time ago I had a commercial integrated amp Atoll IN50, which had a resettable fuse in it, after pushing it hard for some time it cuts the output and then reset after a several seconds of cooling if turn the volume down. Don't remember where it was located, at the speaker output or at trafo's primary, but if I can remember it was rated 3A, so mostly like to be in the OP as it has 160VA 2x30 or 2x35v trafo which is far lower consumption for that.
Probably in the speaker feed to make it "punter proof"
A common use for these polyswitches was in satellite receivers in the feed to the LNB on the dish. If a short occured in the wiring then the supply was protected and when the fault was cleared so the supply came back up. Thats really their intended type of application.
A common use for these polyswitches was in satellite receivers in the feed to the LNB on the dish. If a short occured in the wiring then the supply was protected and when the fault was cleared so the supply came back up. Thats really their intended type of application.
The more overcurrent they are heated by the faster they open...all fuses are like that.
What if the high current were a short. The relay would then try and re-connect the rails into that short. Also the relay control circuit would need to be fed from a reliable independent supply.
I agree....... but then we have slow blow fuse too. and if the slow blow fuse too blows off then, we can feel sure that it is dead short. ( the slow blow fuse will blow off after couple of relay resets.)
Add: OR we can say, depending on the current flow , relay should determine, if it should reset.
Add: OR we can say, depending on the current flow , relay should determine, if it should reset.
If you have a fast acting circuit disconnect then how are you going to set off a slow blow fuse?
Have you ever had a computer power supply that just kept chirping every second or two?
That is an automatic retry on an over current or short circuit situation.
With analog circuitry you can do as I suggested in post #5 and with added digital decision making (4 tries and stop) you can stop it from starting again until an operator reset occurs.
Nothing new here.
But do you need it in your amp?
If you really do then go for it...I will help where I can.
Have you ever had a computer power supply that just kept chirping every second or two?
That is an automatic retry on an over current or short circuit situation.
With analog circuitry you can do as I suggested in post #5 and with added digital decision making (4 tries and stop) you can stop it from starting again until an operator reset occurs.
Nothing new here.
But do you need it in your amp?
If you really do then go for it...I will help where I can.
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