Author Topic: Understanding a fan controller to adjust the temperature response  (Read 149 times)

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Offline Agent24

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  • Country: nz
I have an Anteq Basiq 350 Watt power supply. I've just replaced the capacitors as most of them had failed.
I want to modify the fan controller circuit so that the fan runs faster, but preferably keep some kind of dynamic control so it doesn't just run at full speed all the time.

I've seen a basic modification which is to add a 2k2 resistor in parallel with the thermistor, but I don't know if this will do what I want. I'd also like to understand the circuit in more detail anyway, for my own curiosity.

The schematic I've reverse engineered from the fan controller PCB is attached.
I think I understand most of it, except how to actually adjust it.

Here's how I think it works - if I've made any errors please correct me and explain!...

The 150R resistor provides a minimum voltage to the fan so it cannot stall, even if the controlling transistor is in cutoff.

C1 provides a kick-start feature to ensure the fan runs at full speed for a few seconds at power up, and won't stall if the controller is at minimum speed
(Voltage across the fan was only about 3v when cold)

Once C1 charges, the controller takes effect. However, C1 must be discharged when the PSU shuts down, to ensure the kick-start feature works on next power up.
This is done via D1 and the 3k resistor, while the 300R resistor, R6, keeps D1 reversed biased when power is applied, to prevent discharging of C1 during operation.

I assume R5, being 1%, had something to do with the actual temperature/speed curve. I am not so sure. Some quick research on thermistor circuits suggests this resistor is there to linearise the thermistor's response in the targeted working range.

I wonder now if R1 and R2 may have something more to do with the actual parameters of the fan controller, since the base drive to the A733 transistor is derived at this junction anyhow.
« Last Edit: May 11, 2019, 10:11:19 pm by Agent24 »

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