Simple 3.3V power supply unit


Dilshan Jayakody  writes:

Now a days 3.3V PSU is essential for microcontroller, programmable logic devices and for some analog components also (especially with some new ADCs). This is ultra-simple 3.3V power supply unit, which is suitable for above mentioned experiments. This power supply is based on, ON semiconductor’s MC33269T-3.3 LDO regulator and it is capable to deliver 3.3V output with maximum of 800mA current.
The PCB design supplied with this article is also compatible with LD1117V33 (also known as LD33V) LDO regulator and it can use with this PCB without any changes. Dimension of the given PCB is 70mm × 35mm and it is design with all through-hole components. Our PCB design for this PSU is available to download at

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  1. Is there a standard colour for +3.3V?

    Zero volts [return wire] is black, +5V is red, +12V is yellow…
    Brown, blue and green are Australian colours for 240V mains…
    That leaves orange, violet, grey and white to cover 3.3V and the eventual 2.4V [and 1.8V]. I think I’ll stick with orange as the 3.3V wire for now.

    I can buy a 20W SMPS module [5V @ 4A] but I’d like a 3.3V rail as well. Any suggestions?

  2. The box could do with an on-off switch. For prototyping where you need to test start-up behaviour (either electrical or software), a nice power switch is really a godsend.

    Also, it’s nice to restate current load limits like 800mA, but more important is that if it is to be used for higher loads or higher input voltages, some basic thermal calculations should be made. The article should recommend a heat sink to be used for the LDO.

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