Build Your Own Constant Current Power Supply
ฝัง
- เผยแพร่เมื่อ 20 เม.ย. 2022
- A good addition to your electronics lab or workbench is this constant current power supply built around an LM317 3-terminal regulator chip. In this video we will break down the build and go over the circuit schematic.
The schematic in .PDF format is available from the author via email shown near the end of the video.
Great project, well done!
Thank you. I just used it yesterday to find a dead LED in a TV backlight string. Short the leads, set it to 10 Milliamps and start probing. No matter how many LED's were in the string it still sources only 10 Ma through the whole thing.
Great project
Thanks Larry, It really comes in handy when troubleshooting TV backlight issues. Just short the leads, set the meter to about 15-20 mA's and start probing the LED feed lines. It will light a single lamp or a whole string without changing the setting.
Thanks for your nice video.I also have got this type of ic. l may try it.
I'm finding more and more uses for this than my adjustable, regulated bench supply. It's great for charging batteries & testing for dead LED's in bulbs, TV backlights etc. -- You don't need to know the working voltage of the device under test either. Just short the leads, set it for 15mA & test away! It doesn't matter if there is just (1) or (15) LED's in series, the current remains the same throughout the whole string.
A grand project! What is the transformer from? Doorbell? Thermostat?
That's a really good question! Can't remember to tell you the truth. Suspect it was a clock radio or something but you certainly could use a doorbell transformer. Or if you wanted to limit the voltage just go with a 12V wall wart or similar.
I would the adjustable Pot be easier if you added a 10 turn pot in series or how about in parallel (Shunt) with the adjustable pot to get easier adjust the current more precise?
I didn't seem to have any problem with setting an accurate current reading using just a standard pot but sure, a 10-turn pot will always give you more control.
I have just begun searching for an accurate way to measure µA of current. It looks like I can use the secondary part of this circuit (after the regulator) to build such a circuit using a 50µA F.S. movement. I haven't been able to find much guidance on how to start; but, it looks like the meter portion of your circuit is what I need?
Most meters just use ohms law; V=IR. Using a certain fixed resistor, voltage will be directly correlated to current. For instance, using a 10k resistor, you will measure 0.1-10V for 10uA to 1mA of current. You can switch between resistors if you'd like different multiplication factors.
Also see Dave Jones' ( EEVBlog channel) ucurrent project, he has all schematics practically available; it uses a precision opamp to multiply the measuring-resistors voltage in order to reduce the 'burden voltage' (voltage dropped across that resistor) when measuring small currents.
Hi there, thanks for the video. I did enjoy it so much. Just wondering, will this works as bench adjustable power supply. By adding adjustable volt supply? I really want to build one, so it’s easier when i want to hook it up to any circuit without using individual power supply like individual 9v or 12v or any volt.
Thanks!
Hi U Z, yes this would work if you put it after your voltage regulated power supply circuit. That way you could have a built-in adjustable current limiter too. I have a schematic of my DIY bench supply that I can email you if you post your address here.
I read your comment and question a little closer and would recommend that you build a good (voltage) regulated power supply for your bench. If you hook this constant current supply up to something, like say a transistor radio, the voltage may be way too high and damage it even though the current will be regulated to where you set it. Hope this clears up your question, if not msg. me back and we can talk about it.
How did you make the markings on the front panel?
At the time, I use rub-on lettering but didn't clear coat it (that's why it's wearing off now) but have since found that I can print water slide decals obtained from a Hobby store that are easier and in color too!
@@WestviewChurch have seen these items ever! Maybe in Europe or in my country we don't have them? Any idea how we can do it these days?
That D2 doesn't look like it will protect against reverse voltage. It will block voltage coming in but not reverse voltage. I would think adding a diode in reverse across the output may help. My 2 cents which isn't much :-)
Your partially right, it does block reverse voltage which would ultimately protect the circuitry.
Thank you for sharing this with us. One small modification could be the addition of a momentary push button switch to temporarily short the output terminals while adjusting the current level. One question, is that a wire wound potentiometer?
In this case it IS a wire-wound but it is not necessary since there is little current flowing through it. I just found this one in my junk box. I like the idea of the momentary contact switch to short the leads. Good idea. Also a voltmeter would be of some value too but I didn't have the room for one in this box.
I like it. It looks like it would be a fun project to make!👍
@@ronniepirtlejr2606 It really is easier than it looks and LM317 are widely used and easy to find.
I cannot use this circuit.
the current is big through the potentiometer.
i dont know can use 350 mA carbon potentiometer.
i do parallel connect main resistor.
Iadj is enough small 100uA.
Yes, you may have to use a higher wattage, wire-wound potentiometer because of the current flow through it.
You can limit max current with one resistor ~30 ohm in series with VR (this also slightly increase regulation linearity). And can use this resistor as shunt for ammeter (you always loose 1.2V on VR, so why not use part of this voltage from limiting resistor to drive ammeter?). Maybe use schottky protection diode not in series with current cource, but in parallel with output terminals, in reverse polarity.