Due to low cost and high output current this project is pretty famous in DIY category, and I thought to give it a try too, but a lot of people are connecting so called Load Resistor on the terminal which give the most power as to keep the power supply constantly on, and here the confusion begins, in my SMPS the most power is supplied to 12V rail, but the fan used in SMPS is directly connected to it, and I've read projects in which the similar connection to fan and 12v rail was found.

Question wobbling in my mind is, if there is a load(fan) already connected to the rail with most power and it is constantly on(no temperature control) why you need to add some extra 'Load Resistor'?

Are other makers adding a load resistor just because "Everyone else is doing so I should too" or there is a hidden reason behind it, example- that there should be more than some specific Watts of load and because of that, you need to add a resistor.


Fan current: 0.1A

ATX PSU minimum stable current >= 1A, but YMMV.

Your fan simply does not consume enough current for the ATX regulation to be stable. And most PC PSU designs do not regulate the 12V where the fan sits on, but the +5V line instead.

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  • \$\begingroup\$ "And most PC PSU designs do not regulate the 12V ... but the +5V line instead" I highly doubt that, can you provide a reference? Note that in modern computers, most of the power is drawn from the 12V line, including all of the power for the CPU and GPU. \$\endgroup\$ – marcelm Apr 20 '17 at 16:51
  • \$\begingroup\$ Absolutely not true @marcelm. Most ATX power supplies do however have a co-regulator architecture and you need a minimum load on either 12 V, 5 V or both in some cases. You might read up on this in Formfactors: formfactors.org/developer%5Cspecs%5Catx2_2.pdf \$\endgroup\$ – Jack Creasey Apr 20 '17 at 17:33

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