I'm building an electronics controller. I have a chassis with a 12VDC cooling fan. It seems to me that a fan might present an inductive load to the ACDC power supply it's connected to, so I'm trying to decide if I should include a flyback diode or not. Is it common to add an extra flyback diode just for 12V fans or are they already built in? The fan in particular I'm looking at is digikey datasheet, which says it is "electronically protected" although I'm not sure what they really mean by that. Thanks!
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\$\begingroup\$ the fan contains a controller ... it is not just a motor \$\endgroup\$– jsotolaCommented Apr 1 at 18:43
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\$\begingroup\$ Where would you put a flyback diode? Wouldn't it depend on how you connect the fan to power supply? How are you connecting it? \$\endgroup\$– JustmeCommented Apr 1 at 18:54
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2 Answers
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No. A catch (‘flyback’) diode is not required for a brushless DC fan. The brushless DC fan’s internal circuit isolates any back-EMF that the drive coils might generate even if the power is shut off suddenly. The vast majority of fans on the market today are brushless DC type, including the one you’re looking at.
When do you need a catch diode? If the motor is a brush type (such as you might find in robotics or RC hobby), then you a catch diode to dissipate the back EMF generated when the current is switched off.
“Electronically Protected” means that the fan controller detects if the fan is stalled and will disable it for a time to prevent damage (after which it will 'auto-restart'.)
answered Apr 1 at 18:57
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A flyback diode is normally used to protect a switching device such as a MOSFET or BJT. When the device switches off a large reverse voltage is generated by an inductive load and this can exceed the devices maximum ratings.
So unless you're switching the fan electronically there's no need for a diode.
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\$\begingroup\$ I'm not switching the fan during operation, but the fan is being turned on and off each day with the rest of the controller, so that's where my concern comes. \$\endgroup\$ Commented Apr 1 at 19:11
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\$\begingroup\$ @Open_Hamster3337 But you never answered how you would even connect a flyback diode if it is directly connected to supplies. \$\endgroup\$– JustmeCommented Apr 1 at 19:45
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\$\begingroup\$ I would connect it in parallel with the load, with the fan being the load. It would be reverse biased relative to the 12VDC power supply. Physically I would put it close to the actual load rather than right at the power supply. \$\endgroup\$ Commented Apr 1 at 20:06