Electronics > Projects, Designs, and Technical Stuff

My first power supply

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dom0:

--- Quote from: queennikki1972 on April 26, 2019, 01:02:45 am ---Powers on and functions great, still waiting on my fan to come in.

--- End quote ---

I would recommend a larger heatsink instead of a fan at these power levels, since the thermal resistance (K/W, kelvin per Watt, calculations just work like electrical resistance) of these tiny heatsinks is pretty bad and doesn't improve that much with a fan.

MarkF:

--- Quote from: dom0 on September 21, 2019, 04:33:23 pm ---
--- Quote from: queennikki1972 on April 26, 2019, 01:02:45 am ---Powers on and functions great, still waiting on my fan to come in.

--- End quote ---

I would recommend a larger heatsink instead of a fan at these power levels, since the thermal resistance (K/W, kelvin per Watt, calculations just work like electrical resistance) of these tiny heatsinks is pretty bad and doesn't improve that much with a fan.

--- End quote ---

I agree with @dom0.  Your heatsinks are really small even with a fan.
The LM78xx's are going to get hot if you expect to pull their full power.
It looks like you are using a full wave bridge IC.  It could use a bigger heatsink too.

Here is a picture of a 51mm and two 38mm tall heatsinks on the triple supply circuit I showed earlier.
Even these get hot at or near full power.

queennikki1972:
Also I noticed there is a small spike from the fan noise? on the the 12v side, since thats where the fan is connected. I agree about larger heatsinks as well. Is there anything you can put inline with the fan to suppress the spikes? Maybe a larger output capacitor? It is minimal but just wondering. The 5v side is much smoother.

xavier60:

--- Quote from: queennikki1972 on September 21, 2019, 10:17:39 pm ---Also I noticed there is a small spike from the fan noise? on the the 12v side, since thats where the fan is connected. I agree about larger heatsinks as well. Is there anything you can put inline with the fan to suppress the spikes? Maybe a larger output capacitor? It is minimal but just wondering. The 5v side is much smoother.

--- End quote ---
It's difficult to completely remove the spikes by increasing the output capacitor. It could help.
A simple series resistor will also reduce the spikes. You could experiment with the value. Larger values will give better filtering but also drop more voltage.
A DC choke wold be more effective, but check for excessive spiking on the fan side, A capacitor might be needed directly across the fan also.

Extra: A good option is some series resistance plus a capacitor directly across the fan.

OM222O:
using a common mode choke followed with 4 capacitors and an inductor (2 large value electrolytics / tantalums and 2 small value ceramics) in a pi filter configuration should basically drop that switching noise to nothing  :-+ although I think the pi filter alone should be good enough in this case.

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