Electronics > Projects, Designs, and Technical Stuff
Dual channel 0-15V 0-500mA power supply
kallek:
Hello everyone!
This is my first post in the Forum! :) I want to share you my power supply project progress. I have been using basic Lm317 power supply which i built four years ago, but i want capability to limit current when testing new circuits.
Specs:
- Two independent channels, 0-15V, 0-500mA
- Linear, TIP122 darlington series pass transistors
- Passive cooling, heatsink on back panel
- 40VA 2x15VAC toroidal transformer that I had already
- Zener references
- Lm324 OpAmp for sensing voltage and current, and driving CV/CC leds
- Low side current sensing, seven 10 ohm 0,6W resistors in parallel
- Analog panel meters for voltage and current readings, two per channel
- Switch to short output to set current limit
- Load switch
- Single turn wirewound potentiometers
I have already etched and assembled the circuit board, and it looks like working fine. Schematic is not ready yet, but I will share it when I have finished it. Transformers voltage is slightly low, but not too bad, no large ripple on 15V at 500mA with 3300uf smoothing capacitors. I intend to use toggle switch as load switch. I know it have that contact bouncing effect, but is it too bad practice if it does not overshoot? Next step is get sheet metal for case, and wait panel meters to arrive.
Thank you for advises and comments! :)
David Hess:
--- Quote from: kallek on February 17, 2020, 09:41:38 pm ---- Two independent channels, 0-15V, 0-500mA
--- End quote ---
Were you going to make the channels floating from each other? This had the advantage of allowing them to be combined in parallel for higher current, series for higher voltage, or series for a bipolar tracking.
--- Quote ---Linear, TIP122 darlington series pass transistors
--- End quote ---
10 watts is in the range where integrated regulators which provide built-in thermal protection could be used as pass elements.
--- Quote ---Lm324 OpAmp for sensing voltage and current, and driving CV/CC leds
--- End quote ---
I would not get hung up on using a quad operational amplifier. Some of the better designs take advantage of separate amplifiers with different supplies for each output or the same output.
--- Quote ---Low side current sensing, seven 10 ohm 0,6W resistors in parallel
--- End quote ---
Why require low side current sensing?
--- Quote ---Single turn wirewound potentiometers
--- End quote ---
I prefer good quality single turn potentiometers for coarse and fine control but both methods have their virtues.
kallek:
Thanks David Hess!
--- Quote from: David Hess on February 18, 2020, 05:44:50 am ---Were you going to make the channels floating from each other? This had the advantage of allowing them to be combined in parallel for higher current, series for higher voltage, or series for a bipolar tracking.
--- End quote ---
Yes, I will use them just floating or connect to ground binding post. I assume that this is possible with two separate windings? That is true.
--- Quote ---10 watts is in the range where integrated regulators which provide built-in thermal protection could be used as pass elements.
--- End quote ---
I have to think that.
--- Quote ---I would not get hung up on using a quad operational amplifier. Some of the better designs take advantage of separate amplifiers with different supplies for each output or the same output.
Why require low side current sensing?
--- End quote ---
I have these on hand and layout was easy to make. With high enough value current sense resistor accuracy is about 2mA and current can be set down to under 20mA. I choose low side sensing because then diff. amplifier is not deeded.
--- Quote ---I prefer good quality single turn potentiometers for coarse and fine control but both methods have their virtues.
--- End quote ---
It could be nicer... Good quality pots are not cheap so I try with single pots with big knobs. ;)
Kleinstein:
The LM317 can be used as a kind of protected transistor at the low power. However it may cause a little more voltage lost - so it could be a problem in this example with a relatively low transformer voltage.
I like the choice of low current and voltage for a beginner's project :clap:. so less of the magic smoke to escape.
With separate windings one could use the 2 supplies in series / floating. However the maximum permissible voltage between the 2 parts may be limited.
MarkF:
Pictures broken...
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