Internet PLC Forum
General => Technical support => Topic started by: jonathan.kaye on July 26, 2015, 06:16:36 PM
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I have a FMD 88 and my cabinet is getting a little hot in the summer. I think having the PLC turn on a fan after set point would be neat.
I'm out of digital outputs though. I am wondering if I can write a ~3V signal to a small cpu fan. Digikey has fans that run down around 0.1 Watts. If this is to much power could I maybe toggle a transistor?
I couldn't find anything in the manual on the current draw for the two D/A outputs.
Thanks for any help!
-JK
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The DAC output is not usually designed to deliver much current. DAC 1 & 2 uses opAmp to buffer the outputs so they each should be able to output 10mA. At 3.3V 0.1W fan will need 30mA which is too high for the DACs.
You can actually connect a simple N-channel MOSFET such as the IRLU024N. The DAC output can be used to drive the gate of the MOSFET. When DAC output = 0V the MOSFET is OFF and when DAC output = 5V the MOSFET will be turned ON and that will allow it to drive a pretty big fan.
An IC such as ULN2003A can also be used instead of the MOSFET. It is really simple to interface and have built-in diode to absorb the inductive kick from driving the fan.
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Alright!
Squeeze one more output in.
Thanks.