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Old 02-12-2016, 07:04 AM
Nath2099
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Constant Current PSU voltage drop on low load

This isn't exactly an astronomy project but i hope I'm ok to post.

I am building a wireless dmx system using
these components:

DMX Controller
2.4G nRF24L01 Wireless Module w / PA and LNA
Arduino Pro Mini
50W DC 30-36V 1500mA high Power LED Constant Current driver AC 85-265V IN
This is not the exact one, but a 50W constant current supply
50W RGB LED Flood Light

The issue I'm having is that when the LED turns off, the voltage that supplies the Aduino/RF circuit drops from 5/3.3v to about 1.9v. I assume this has something to do with the constant current supply. Is there some way I can induce a current accross the supply when the LED turn off?

Here is the circuit for the Arduino/RF board:

http://forum.arduino.cc/index.php?ac...;attach=121416

Thanks in advance for any advice!

EDIT: I should add, the entire thing including the DMX controller and Arduino/RF board are being supplied by the 40V 50W constant current PSU. The DMX Controller works fine whether the LEDs are on or off.
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Old 02-12-2016, 08:43 AM
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iborg (Philip)
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Hi
Have you considered switching the power supply output between a shunt load (high wattage resistor) and your flood light?

Not exactly elegant, but, might work.

Another possibility, a separate supply for the controller.

Philip
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Old 02-12-2016, 08:56 AM
Nath2099
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Hi Phillip, thanks for your reply. A second PSU would be the ideal answer, but I'm out of space. I will have a look at the shunt idea. I just noticed on the image of the DMX controller there is what looks like an inductor of some description. Could that be what's letting the it keep working when the Arduino/RF board doesn't, maybe?

Thanks!
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Old 02-12-2016, 10:53 AM
Nath2099
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A mate just pointed out that the LM78XX series regs have a max 40V input. So I think what might be happening is that when the LED is on the voltage is <40V, and when it's off the voltage creeps >40, freaking out the reg... Maybe...
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Old 02-12-2016, 11:22 AM
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iborg (Philip)
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Hi

I don't know what effect the inductor may have, sorry.

Assuming that the Arudino only needs a smallish current and that the input for Arduino voltage is going too high, try a voltage divider across the output from your power supply.


A Zener diode may be another option

From https://en.wikipedia.org/wiki/Zener_diodeVoltage shifter A Zener diode can be applied to a circuit with a resistor to act as a voltage shifter. This circuit lowers the output voltage by a quantity that is equal to the Zener diode's breakdown voltage.
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Old 21-12-2016, 11:26 AM
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I fixed this by using a 60V input buck regulator.
http://au.element14.com/texas-instru...-4v/dp/1469167

Just in case anyone ever stumbles across it.
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Old 21-12-2016, 12:46 PM
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Constant current supply has only one thing constant, and that is output current.
Voltage at output will vary with load, according to formula:

V = Load * Current

Lower load (higher load resistance), higher voltage (because current should remain the same

So.. you are lucky you didn't destroy something with high voltage spike, that appeared after removing the load (LEDs), most likely there was an over-voltage protection somewhere that lowered the voltage.

Last edited by bojan; 21-12-2016 at 12:59 PM.
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Old 21-12-2016, 01:33 PM
Nath2099
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Hi Bojan, the PSU measures 40V with no load, and the buck reg has an input voltage of 60V. Are you saying that there could be an issue here as well? I was monitoring the heat and it seems OK... nothing gave up the magic smoke...
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Old 21-12-2016, 01:37 PM
Nath2099
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Quote:
Originally Posted by bojan View Post
So.. you are lucky you didn't destroy something with high voltage spike, that
I did kill a few bits trying to work out what was happening! Luckily not expensive bits!
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Old 21-12-2016, 01:57 PM
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Quote:
Originally Posted by Nath2099 View Post
Hi Bojan, the PSU measures 40V with no load, and the buck reg has an input voltage of 60V. Are you saying that there could be an issue here as well? I was monitoring the heat and it seems OK... nothing gave up the magic smoke...
Probably not in terms of input overvoltage, but regulators are sometimes sweating too much in cases of inpur and/or output transients (line regulation)... So it is better to keep them at practical minimum.

I would take input voltage for Arduino from more constant voltage source, and use constant current regulator for LEDs only (you sort of did it by using buck regulator).

If you must use the constant current line for whatever reason, a resistive load or Zener diode (as suggested by iborg) is good option...
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Old 21-12-2016, 02:23 PM
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No worries, The reg I'm using has a feedback loop on the output side which I thought was to minimise the effects of a fluctuating input voltage...?

As you can see, I don't really know what I'm doing... just making it up as I go!
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Old 21-12-2016, 02:31 PM
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Originally Posted by Nath2099 View Post
No worries, The reg I'm using has a feedback loop on the output side which I thought was to minimise the effects of a fluctuating input voltage...?..
Yes, that is true of course but you must not forget about delays in feedback loop, which compromises the input voltage regulation, and resulting output peaks are quite possible and may be dangerous in some cases.

"Good design practices" comes to mind ...
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Old 20-12-2019, 07:14 PM
Cynthiada (Damla Lee)
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I also agree with the idea of the shunt.
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My stepper motor website:skysmotor.com - Machinery Design ? - ? Stepper Moter Development

"Necessity is the mother of invention." - Author unknown.
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