Electronics > Beginners
uSupply Problems
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Dave:
Find service manuals of old HP power supplies. E3610A, for example - simple and elegant design.
hugo:
Not a micro but a better supply:

DC2132A  24V 3A Constant Voltage, Constant Current Bench Supply Featuring LT3081, LT8612, LT3092



 
VEGETA:

--- Quote from: Jwillis on May 01, 2018, 02:57:16 am ---Did you consider the L200.It has an output adjustable current up to 2 amps .Can be pulled to 0 Volts with a negative rail .http://www.st.com/resource/en/datasheet/l200.pdf

--- End quote ---

I like that IC so much, it could be the best to use for such projects.

I plan to use one to create my lab power supply, there is a schematic for using it as so. It uses 10k and 100k pots to adjust voltage and current respectively.

I want to never use a regular pot, but a digital potentiometer! this way I can set everything via software very easily. There is MCP41100 and MCP41010 on aliexpress for very cheap. This is my idea after thinking about it so much.

This way you are following the datasheet and most importantly without any op-amp or stability issues!

What do you think?
Kleinstein:
When using Digital pot to adjust voltage and current limit, one has to observe that those digital pots are limited to voltage within the supply range of the chip and thus with many chips to a 0-5 V range. Especially the higher value digital pots can be effected from parasitic capacitance and this might cause stability problem - it depends on the circuit: in some circuits it is not a problem, other circuits can suffer.

The L200 is nice for a beginners project. However the accuracy of the current limit is still limited and the range for adjustment is not very large. So for a larger current range one would need something like a switchable shunt.  Also AFAIK the voltage range of the generic circuit does not go down to 0 V - so it needs some additions to make is work down to 0 V. Also self heating limits the stability / precision as the whole circuit gets hot, not just the power stage.
VEGETA:
You would need a negative rail to get it to 0v, which is doable. I saw TL431 or so used to achieve this... make it -5v and it will be enough.

I don't understand why digital pots are a problem of stability. They are simply resistors.

Current limit will have a drop voltage of around 0.43v between pin 5 and 2, so it won't be a big problem. However, the bench psu circuit shows more details and more resistances with an op-amp... but it won't get worse.

getting 10k for voltage control and 100k for current will guarantee 30v 2A, but I don't fully understand the current limit control loop. I would like a nice explanation for it (the bench psu config.)

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