0-20V 3A bench PSU


Posted on Feb 5, 2014

It`s a little late to calculate ohm`s law right now, as far as I can see 24V/2A should dissipate 1, 88W in the 0, 47 ohm resistor and 4W in the 0, 1 ohm resistor. I wouldn`t use the Lm723 chip. The Fairchild uA723 was amongst the earliest analog ICs - it iwas released almost 50 years ago and the performance is not great. It is the same vintage as the uA709 opamp and be very greatful you will never have to use a uA709.


0-20V 3A bench PSU
Click here to download the full size of the above Circuit.

The 723 gain is limited so it is not a great regulator, and you cannot adjust down below 2v. If you are going to build a power supply, it is far too much effort to end up with a fairly poor supply that cannot regulate to 0V. The 723 current limit is very crude and it will drift noticeably as the supply warms up. The use of a power supply as a stable current source is a very useful feature. It takes a really good heatsink to dissipate the power in the 2N3055 and so I would recommend multiple 2N3055 devices with 0. 1 ohm emitter resistors (as in the 723 circuit) to replace a single 2N3055. You will need either a big passive heatsink, or a good CPU cooler can handle the power as well. The driver transistor needs to be on a heatsink as well. The DIY design does go down to 0V, it does have a good quality current limit, it has a much higher gain regulator so you will get better DC regulation, it looks like it has proper frequency compensation. It looks like power on transients has been considered. I think it is probably not a bad design at all. I wouldn`t use the Lm723 chip. The Fairchild uA723 was amongst the earliest analog ICs - it iwas released almost 50 years ago and the performance is not great. It is the same vintage as the uA709 opamp and be very greatful you will never have to use a uA709. It would be useable, but the diy design is probably so much better that it is worth the effort. The 723 circuit looks simpler, but...




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