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Important changes (and why it's going slow at the moment)

A project log for ElbSupply - Simple linear bench supply

This project aims at building a rather simple yet useful bench power supply for everyday tinkering.

EliaElia 04/30/2015 at 17:540 Comments

It's been almost two weeks since the last update so I thought I should give a quick overview of what has happened.

I have exchanged the LT3083 with the much cheaper LM350T. The original idea to using the LT3083 was that this regulator could be adjusted down to 0 volts without much effort. As it turns out for true 0V output even with the LT3083 I need to power my op amps from a negative rail to pull the SET pin sufficiently low.

After thinking about it a bit seeing that there was no way to get around implementing another DC-DC converter to invert the input voltage and generate a negative voltage for the op amps, I decided to change out the regulator because now the LT3083 was not really convenient any more but just an expensive LDO.

The negative supply is provided by the venerable MC34063 in an inverting configuration. I have also changed out some of the op amps. What's left are a LM324 for setting and regulating the current and voltage and a LM358 for the PWM buffers.

I have also thrown in an LM4040 2.5V voltage reference so I can have some confidence in my measurements and set point offset. I'm not sure why I originally skimped on that in revision A, probably I wanted to save a bit because of the expensive LDO.

I have started the layout but it is only slowly creeping forward because I am really busy with studying for university. After a whole day of studying, PCB layout isn't exactly what I define as a relaxing activity.

As always all the current development hardware and software files can be found on GitHub.

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