Electronics > Projects, Designs, and Technical Stuff
Simple DIY Linear PSU
panoss:
I want to build a relatively simple Linear PSU having the ability of transformer taps' switching (I have a transformer with output of 30V with a center tap, so it's 0-15 and 15-30).
I 'm in the process of building this power supply. Relatively simple, has tap switching and works ok (according to the writer).
What do you think?
Can you see anything wrong with the schematic?
Maybe someone has built it?
Zero999:
It looks reasonable to me, although the transformer will multiple secondary windings, with odd voltages might be difficult to source.
I would probably have used a comparator such as the LM393, rather than the LM324 op-amp (seems odd they're using a quad, rather than the dual LM358, as only two are used) and some PNP transistors to drive the relays.
panoss:
--- Quote from: Zero999 on March 05, 2020, 11:19:18 am ---the transformer will multiple secondary windings, with odd voltages might be difficult to source.
--- End quote ---
What do you mean by 'odd voltages'?
Should I stick to the exact voltages (of the transformer) shown in the schematic?
I 'm planning to use the transformer I mentioned, a 0V-15V-30V. (that is a 30V with center tap)
And a second small transformer for the 21.7V that feeds the 7818.
kallek:
I am not very familiar with lm723, but I still want to mention what I think. I think that even with center tap transformer, these transistors have too much heat to dissipate.
You have few options.
- Add thermal protection, the simplest solution is mechanical thermal switch.
- Use big heatsink and more transistors, and maybe transistors with lower junction-to-case thermal resistance.
- Reduce maximum current.
I would myself add a fuse to the secondary side also. Often with big transformers your primary fuse have to be quite high value so it does not blow from inrush current.
That 0.18 ohm 5W resistor have to be current sensing resistor. It will be very hot with max current and therefore not very accurate. For example, three 0.56 ohm 5W resistors in parallel would be better solution.
Edit. I would also add protection diode over pass transistors.
coromonadalix:
This psu design is good, not perfect, many companies use switched xformer secondaries to limit thermal dissipation at low voltage output ,,, you have some models with 5 secondaries taps ...
The lm 723 design(s) are proven, you can add some trick(s) to get it down to zero volts etc .... this psu as a floating supply design for the regulation section, it give better stability.
You could help the cooling with an temperature controlled fan on top of the heatsink, or add an small temperature controlled fan driver board ...
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