Power Supplies: 2 Switchers 1 Linear 40mm Cooling Fan


Senior Member
hi folks,
WARNING: If you use the USB connector output option on the KYK_PDM7 board described below, DO NOT connect anything UNTIL AFTER YOU HAVE ADJUSTED THE OUTPUT TO +5v !!!! This is a +5v output only, NOT a USB communications connector (Data+ Data- are not connected).
Since this is a very generic & rudimentary project, I’m not going to go into a lot of detail. If you want to study the inner workings of power supplies, there’s plenty of good Youtube videos.
If you are new to electronics, you may be asking yourself “When should I use a linear power supply & when should I use a switcher?” Also, since switchers have become so cheap & much more efficient, why would I ever want to use a linear supply?
Well, in my opinion (but you know what they say about opinions) modern switchers have become so good & cheap that in almost all cases, a switcher is a no brainer.
The primary disadvantage to switchers is high-frequency noise. If you are going to be driving a power servo or a microprocessor controlling discrete IO, the switcher usually works fine.
However, suppose you are building a calibrator or Wheatstone Bridge that’s outputting millivolt signals. Well, maybe the rock-solid DC output level of a linear supply could make life easier. Heck, a battery is a great linear supply & sometimes I’ve even used a spare op-amp & LM334 to make a +3 volt supply that holds constant with +5…+32vdc input, so as the Brits & Aussies say “Bob’s your uncle”.
Guess it all depends on what you’re building.

I like to use the elderly 7805s with circuits that don’t draw much current. As long as you aren’t drawing but a fraction of the max current, the heat’s not an issue. However, once you start pumping amps, heatsinks & fans may be needed. That’s the price to pay for the quiet output.

Anyhow, this project presents 3 power supplies & a 40mm fan board that mounts to any of the supplies.

The “KYK” prefix used on all 4 boards just means the mounting holes match other boards I’ve made in the KYK series (for boating & other outdoor projects). So, for example I can stack a power supply on top of a 20M2 KYK board & drive interface. It just makes stuff quick & easy to bolt together.
The PDM suffix means “Power Distribution Module” (i.e. a board that supplies +5 +12 etc. to other boards in a project). Of course, the FAN suffix means a (in this case 40mm) fan board that bolts to any KYK board. The 1 3 7 8 (etc.) final suffix specifies a particular type of PDM FAN etc.

The two switchers KYK_PDM7 KYK_PDM8 (3A & 5A) presented in this project use Chinese boards I adapted to host boards with terminal strips & fan connectors. The (PDM7) 3A switcher also has the option of adding a USB Type A Female for +5v output. (Links to the boards in the .pdfs)

The linear supply KYK_PDM3 I typically use with either a LM323K T0-3 metal can (3 Amp) or MC7805 T0-220 (+5v @1A) or MC78T05 T0-220 (+5v @3A). Any may be used with heat sinks. Of course, other fixed voltage linear regulators may be substituted.
The 40mm fan board KYK_FAN1 will mount onto any of the 3 power supply boards. For example, if you are using +12v input power, connect a +12v fan. Just makes adding a fan easy.

A word of caution about Chinese parts… If you order a dozen parts of the same type & can’t get any of them to work, don’t assume it’s something you’re doing wrong. I don’t know if some vendors just don’t have quality checks or what, but sometimes you just get a bad batch. My worst experience was a group of “Analog Devices” parts that were not even the parts silk-screened on the chips (however, after my complaint the vendor did send me the real thing).
It’s the world we live in, so buyer beware.