Help me with a fan driver please

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#1
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Hi Everyone,

I finally figured out how to GPSDO my rubidium oscillator so I'm going to make an extra box that contains the GPSDO, RS422 to TTL serial, and a fan controller.

I'm going to sense the temperature using an ADC and then adjust the PWM of fans accordingly in an attempt to keep the temperature stable. It will be a 5V project, but I will have 24V available as well.

Should I use a 5V or 24V fan? I think I could use a 24V fan if I used a high or low side driver although I don't recall exactly which one without looking it up!

This is a one off project, should I use a transistor to switch the fan or a mosfet? What calculations do I need to do to make sure the device will not overheat?

Digikey has 60mm square fans from:

5V - 0.4W to 1.75W
25V - 0.72W to 10.3W!

I don't think I need any sort of beefy fan though...

Thanks,

Alan

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Most temperature controlled ovens keep the oven ABOVE ambient with big hot resistors dont they? Like at 90 deg F. It doesnt get that hot up in the great white north does it?

Imagecraft compiler user

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Take a look at the TC665. I am using one in a project and you might like some of the features in it. For temp measurement a DS1820 maybe?

The TC665 can run your higher voltage fans with no issues

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Hi Guys,

I'm trying to stick to protoboard/pth for this one off project. I've got lots of PN2222A laying around. If I power the fan with +24VDC and then use a PN2222A to switch it to ground, is this a low side driver? For heat dissipation do I need to measure the voltage going through the transistor * current?

Thanks,

Alan

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Quote:
measure the voltage going through the transistor * current?

measure the current going through the transistor * voltage (across the transistor)!

Einstein was right: "Two things are unlimited: the universe and the human stupidity. But i'm not quite sure about the former..."

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DO1THL wrote:
Quote:
measure the voltage going through the transistor * current?

measure the current going through the transistor * voltage (across the transistor)!

Yep, I had that backwards!!

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High and Low Side Drivers:

JC

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So, NPN as a low side driver. I've attempted to drive motors with BJTs with different motor voltage and signal/control voltage and run into various issues that are vague and fuzzy in my memory at the moment. Stupidity is always a possibility :)

So the PN2222As are TO92s? 600mA enough? As long as you drive it into saturation it should work, right? I suppose they are driven by current, so you have ~0.6V Vbe, figure out desired Ie and divide by some factor (10, let's say) to find Ibsat to ensure saturation. Then Kirchoff's voltage law and Ohm's law to figure out Rb to achieve Ib=beta*Ic based on control voltage.

After spending a fraction of the time getting a MOSFET to work right--the first try--on a < 5V small motor I think I'll just do that from now on. :) I'll help if I can but... probably much smarter folk on here who can get you what you need.

It should work - bot-thoughts.com