This part is used across the biasing transistor of APT 1 amplifiers to reduce gain if the heatsink exceeds 85 deg. C, in which the resistance falls from 130-150kOhms to less than 100 Ohms, to reduce the input signal.
Of course, the part is no longer produced, and my attempts to get one of the original manufacturers to help me find a suitable replacement haven't yielded results. Is anyone familiar with a replacement to this part, which is missing from the amps I'm working on? The original is the one with the tab, but I can adapt mounting for other types if they are electrically similar.
Thanks!
Of course, the part is no longer produced, and my attempts to get one of the original manufacturers to help me find a suitable replacement haven't yielded results. Is anyone familiar with a replacement to this part, which is missing from the amps I'm working on? The original is the one with the tab, but I can adapt mounting for other types if they are electrically similar.
Thanks!
Hello GKTAUDIO,
I had some difficulty finding an equivalent for a different PTC thermistor, however what I found was the EPCOS/TDK Series B59052D1. The case has a metal tag for mounting to heatsink, would this work for you?
According to TDK's product brochure attached, the B59052D1080A040 has a T Sense of 80 Deg C while the B59052D1090A040 has a T Sense of 90 Deg C, both devices advertise the resistance dropping rapidly to below 100 ohms.
Either of these devices seem to be available in any quantity from the reputable suppliers, for my application I ordered a set of 4 of the B59052D1080A040 (80 Deg C) PTC thermistors, please see image attached.
Hope this helps.
Thanks,
John
I had some difficulty finding an equivalent for a different PTC thermistor, however what I found was the EPCOS/TDK Series B59052D1. The case has a metal tag for mounting to heatsink, would this work for you?
According to TDK's product brochure attached, the B59052D1080A040 has a T Sense of 80 Deg C while the B59052D1090A040 has a T Sense of 90 Deg C, both devices advertise the resistance dropping rapidly to below 100 ohms.
Either of these devices seem to be available in any quantity from the reputable suppliers, for my application I ordered a set of 4 of the B59052D1080A040 (80 Deg C) PTC thermistors, please see image attached.
Hope this helps.
Thanks,
John
I think you have a problem. Assuming that R25 = 150k and R85 = 1.5k (based on your comment and the datasheet excerpt),
B25/85 = 1779.7 * ln (R25/R85) ~ 8200, which is much lower than the values shown for NTCs available from Digikey/Mouser. You can get NTCs that have an R25 value of 150k typical (so you start out OK) but the resistance does not drop far enough at 85C to be comparable.
B25/85 = 1779.7 * ln (R25/R85) ~ 8200, which is much lower than the values shown for NTCs available from Digikey/Mouser. You can get NTCs that have an R25 value of 150k typical (so you start out OK) but the resistance does not drop far enough at 85C to be comparable.
How about this as a solution:
Fit F20B065053600060 on the heatsink. And wire a 100R resistor in series. When the thermal switch gets to 65degC it goes from open to closed and you get your 100R connected from the base to ground of Q1.
I suggest 65degC because that would meet the CE standard for safety.
Fit F20B065053600060 on the heatsink. And wire a 100R resistor in series. When the thermal switch gets to 65degC it goes from open to closed and you get your 100R connected from the base to ground of Q1.
I suggest 65degC because that would meet the CE standard for safety.
Hey there, @VivaVee. That sounds like a very suitable solution. It will be a more noticeable error correction, as well, since it will be passing either full signal or severely reduced at 100R to ground. I will get a couple of these and give them a try.
Thank you for your continued noodling on this - very much appreciated!
Cheers,
Greg
Thank you for your continued noodling on this - very much appreciated!
Cheers,
Greg
