What does the missing thermistor do? (PC power supply)
 

I have some 350W Fortron-Sparkle model FSP-350BU PSUs with empty spots
where a thermistor and fixed resistor would normally be connected in
series, and I'd like to know their purpose. I think that they connect
this way:

http://static.flickr.com/39/83308555_59e5e557a6_o.jpg

Capacitor C10 and pin 18 are on the small vertical circuit board
(beneath the removed fan controller board in the photo below) housing
the Fairchild KA3511DS PSU controller chip, and according to the
datasheet at

http://www.ortodoxism.ro/datasheets/...ild/KA3511.pdf

pin 18 is the Extra Protection (EP) input, which, when its voltage goes
high enough, is supposed to shut down the PSU. In other words, this
seems to rule out the thermistor being used as a overheat sensor
because the pin 18 is low anyway in normal operation.

Here are where the missing resistor and thermistor are located (circled
in red):

http://static.flickr.com/39/83310554_91d773cf62.jpg

This thermistor is not for fan speed control -- that's handled by
another thermistor (next to the screw on the heatsink, higher up in the
picture).

What does the missing thermistor do? (PC power supply)
 

On 7 Jan 2006 19:52:47 -0800, "larry moe 'n curly"
put finger to keyboard and composed:

I have some 350W Fortron-Sparkle model FSP-350BU PSUs with empty spots
where a thermistor and fixed resistor would normally be connected in
series, and I'd like to know their purpose. I think that they connect
this way:

http://static.flickr.com/39/83308555_59e5e557a6_o.jpg

Capacitor C10 and pin 18 are on the small vertical circuit board
(beneath the removed fan controller board in the photo below) housing
the Fairchild KA3511DS PSU controller chip, and according to the
datasheet at

http://www.ortodoxism.ro/datasheets/...ild/KA3511.pdf

pin 18 is the Extra Protection (EP) input, which, when its voltage goes
high enough, is supposed to shut down the PSU. In other words, this
seems to rule out the thermistor being used as a overheat sensor
because the pin 18 is low anyway in normal operation.

Here are where the missing resistor and thermistor are located (circled
in red):

http://static.flickr.com/39/83310554_91d773cf62.jpg

This thermistor is not for fan speed control -- that's handled by
another thermistor (next to the screw on the heatsink, higher up in the
picture).

I suspect the PT (extra protection) input may be a current sensing
input. I don't understand the purpose of the thermistor, though,
unless it is there to derate the PSU at higher temperatures.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.