• Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
    Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.

Missing thermistor from Fortron PSU

L

larrymoencurly

[H]ard|Gawd
Joined
Jul 18, 2002
Messages
1,635
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:

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 URL=http://www.ortodoxism.ro/datasheets/fairchild/KA3511.pdf]Data sheet for KA3511DS[/URL], pin 18 is the Extra Protection (EP) input, which is supposed to shut down the PSU if its voltage goes high. 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):

83310554_91d773cf62.jpg
 
Given the diagram, and the thermistor's proximity to the secondary heatsink, it's gotta be overtemp protection - it's the only thing I can think of anyway. The thermistor (PTC type anyway) should allow voltage at pin 18 to increase as it heats up based on that schematic and the setting of the pot. With the thermistor absent, it seems logical to me the pot is set just below the value pin 18 requires to trip. Otherwise, in normal operation the thermistor would bleed off some power to ground (and less as it heats up and increases in resistance).
 
You must log in or register to reply here.
Back
Top