Connect with us

PWM setup

Discussion in 'LEDs and Optoelectronics' started by NeilMac, Aug 28, 2018.

  1. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Hi!
    Its been decades since i did electronics so rusty in many areas.
    I started up a week ago in the interest in working with LEDs, specific IR for security camera I put together for a Raspberry Pi.
    Problem is I picked up a LED driver with PWM and have not been able to figure out how to setup the "PWM" never used them before.
    I have 4x3W Star LEDS setup and when apply the power the LEDS are bright briefly and then drop to a low glow. I have nothing hooked to the PWM pin since I have no idea and dont want to experiment with it and potentially fry it.
    Thanks!

    pwm-driver-connection.jpg
     
  2. Minder

    Minder

    2,807
    583
    Apr 24, 2015
    It would appear you need an off board PWM controller of some kind, lots of 555 based out there via Google.
    M.
     
  3. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Was wondering about using a 555, would be nice if their was instructions to set it up though, frequency etc. Probably still have a 555 setup in my parts box some ware.
     
  4. Minder

    Minder

    2,807
    583
    Apr 24, 2015
  5. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Thanks.
     
  6. dave9

    dave9

    710
    159
    Mar 5, 2017
    It might have helped if you had provided specs for the driver and/or linked to it.

    There are versions of this board with default drive at 700mA without any PWM input, and some at 300mA, and possibly other current levels up to the max the U1 regulator IC can handle. It appears to determine current based on the values of the two resistors in parallel in the feedback loop, which it compares to the IC's internal reference voltage. You do not need to use the PWM control to achieve the default current yours is set for. 300mA and 700mA are just ballpark figures, these drivers are not that precise.

    If your LEDs have proper heatsinking (so they don't burn up) you should be getting a useful level of output from them. However, they're infrared right? Did you expect to see infrared with the naked eye? It depends on the wavelength. Some will be near enough to the visible red spectrum (up to 700nm or so) that you can see them light up. Some will not.

    You should measure the current going through them as indirect evidence they are producing IR, or of course use an IR sensor to detect it like the camera which we assume can do that (unless it has an IR filter on it, most daytime use cameras do and better cameras capable of both daytime (filter blocking IR) and night time IR have a 2nd sensor w/o the IR filter so IR doesn't spoil the daytime image).

    The versions of your pictured driver that I saw share the following in common:

    - Input Voltage 7V to 30V
    - Output Voltage 1.2V to 28V

    You didn't mention the IR LED specs either, but let's suppose they have a forward voltage of 1.5V. With 4 in series you would then have 6.0Vf.

    If you can find specs for the driver that tell you its minimum voltage drop then you know the minimum input voltage to the driver that you need for a series of 4 IR LEDs. For example suppose the driver loss is 2V which I get from the max input voltage minus the max output voltage. This would mean you need at least 8V input (if their Vf = 1.5V) to drive the LEDs and a bit over 700mA (if it is set to 700mA, or a bit over 300mA if set to 300mA, etc). However one page I saw this driver on, suggests you get best efficiency with at least 3V more than the sum of the series LEDs Vf which would be at least 9V input (again if each LED Vf = 1.5V).

    The higher the voltage the lower the current will need to be. Frankly I would try using a 12VDC, 1A wall wart style switching power supply, because they are so common, inexpensive, and provide sufficient margin that you wouldn't need to know the exact IR LED Vf.
     
    Last edited: Aug 29, 2018
  7. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    The set Im experimenting with are 4x3W Star Leds in the 660nm range and require 2.0v - 2.5v and 700mA each. Im using a transformer thats 12.6v and 2.1 amps. So they glow bright red and are visible.
    The driver was recommended by the person that I got the LEDs from, looking at the specs right now shows it might be a problem, 3w "high Power" driver,"Output Current: 700mA (for 3 watt LEDs)", Output Voltage: 1.2v to 28v DC.
    Thanks!
     
  8. dave9

    dave9

    710
    159
    Mar 5, 2017
    That's not a problem. It is set up to output 700mA for as many LEDs as you want to attach, up to a series of LEDs whose sum forward voltage does not exceed 28VDC, and as mentioned previously your PSU input voltage must be a few volts (2V to 3V) above that.

    Measure the circuit. Measure the input voltage to the driver while it's trying to power the LEDs. Measure the output voltage from the driver while trying to power them. Measure the current flowing through them.

    Unless the driver is just defective, or one of the LEDs damaged, something is wrong. You can jumper around any of the LEDs in series and the remainder should still get the same 700mA because it's a current regulating driver.

    Try that, jumper across one of the LEDs in series, its positive and negative connection and see if that helps. Do it for each LED, one at a time. If that helps, either the LED you jumpered across is damaged, or by doing so you have reduced the Vf of the series down below what the driver board needs, which would mean you need higher than a 12.6VDC PSU.

    While you didn't exactly state it, by "transformer that's 12.6V and 2.1 amps" I assume you mean a complete DC power supply or you have added rectification diode(s) and a capacitor between the transformer and driver circuit, so it's getting DC instead of AC.

    I am wondering though, for IR illumination, why pick LEDs into the red spectrum? This will give you less, useful, IR light for the power consumption. Then again I don't know much about camera wavelength sensitivity, I could be wrong.
     
  9. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Thanks!
    Il do the jumper test later this afternoon. yup lol its DC power supply without a box, its 40 years old but works.
    I have LEDs in the 940nm range, no problem with them just plug into 12v power supply, their not powerfull enough though.
    the 660nm are for plants to be used once winter comes in (around the corner) and I have to bring in some pots. Once I get this problem figured out Il get some other spectrum's and put together a rack for them.
     
  10. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Dont know whats going on, now nothing lights and the driver heats up allot, so something is now shorting. Checked wiring several times, not much to go wrong and I haven't changed anything from last time.
     
  11. dave9

    dave9

    710
    159
    Mar 5, 2017
    Oh well, at least it wasn't an expensive driver. What I would do now, is get one that can operate from 120VAC and not use the old 12.6V PSU, which should greatly increase the efficiency. Without looking around for the best price, I mean something similar to the following "10W 3-4x2(3)W 600mA 9-13V" for the 4 LED in series, here:

    https://www.ebay.com/itm/High-Power...tant-Current-COB-Chip-LED-Driver/122480543106

    However now that I know you're using it for plants, a mere 4 of those is not much light. If you're going to be adding more then I'd get a driver capable of more LEDs instead.
     
  12. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
  13. dave9

    dave9

    710
    159
    Mar 5, 2017
    Those won't work, are just 12VDC power supplies, do not regulate current. I mean you could use one, then a series resistor or another driver module like the one that's blown, except we didn't really determine that it is suitable at 12.0V input for those 4 LEDs in series.

    I do not understand what this means. Yes perhaps 4 x 3W LEDs would be enough to overwinter a plant on the corner of your desk. 600mA, sure I would sooner use more LEDs and less current because heatsinking becomes easier, but the main thing was the one I linked regulates to 600mA (roughly) current. When you put the LEDs in series this means each gets 600mA through it.

    The ebay naming conventions for these drivers is poor. The main thing is it can support up to 13V as a sum of the series LED Vf, and at 600mA. You could look longer for something else but it starts getting into a gray area because if your LEDs are spec'd for 700mA, with 2.5Vf, they are not 3W LEDs. 700mA * 2.5V = 1.75W
     
    Last edited: Aug 30, 2018
  14. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Yup Ive wondered about that and I know others have commented on other LEDS that say their certain wattage and it does not add up.

    So then this one will do?
    Looking at 20W Full Spectrums, 2X

    Thanks!
    Screenshot from 2018-08-30 16-52-35.png
     
  15. dave9

    dave9

    710
    159
    Mar 5, 2017
    I am not sure if that one will work or not because it's cutting it close, with a max voltage of 10V and your LEDs could be right near their upper Vf range at 900mA drive current. It should work for at least 3 in series. If you can dig up a proper datasheet for the LEDs with a voltage vs current graph that might help, though there will still be some variance from one specimen of LED to the next.

    I don't know what significance "Looking at 20W Full Spectrums, 2X" has? More text is more better.

    Personally I would be inclined to use twice as many LEDs at half the drive current. Reducing thermal density reduces heatsink requirements and promotes higher LED efficiency and lifespan, particularly for generic Chinese LEDs (if that's what those are). If you ran them under 2W each, you shouldn't even need more than ~1.5mm thick sheet aluminum, a housing as all the heatsink needed.
     
    Last edited: Aug 31, 2018
  16. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
  17. dave9

    dave9

    710
    159
    Mar 5, 2017
    Yes either of those should work for 12 LEDs in series including the 4 you already have, which one depending on whether you want 300mA or 900mA.

    Keep in mind that those heatsinks were listed for 1W/3W/5W LEDs, meaning one 5W, while 12 LEDs at 900mA is going to be higher than 5W per heatsink if split between the two, but then you're going to need a lot more heatsink anyway to handle the two full spectrum LED modules you just linked.
     
  18. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    I got some old cpu's some ware, I can grab the heat sinks from them :)
    ok ordered two of them :) "12W 7-12X1W: 300mA DC 20-42V 30W 6-12X3W: 900mA DC 20-42V"
     
  19. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Still waiting for delivery ......
     
  20. NeilMac

    NeilMac

    27
    1
    Aug 28, 2018
    Got my driver today.
    Hooked up and it flashing, read some ware that the driver is protecting itself by reseting while too much current is being drawn.
    Does not make sense, four lights are 12W and driver is 12 W ??
    Thanks!
    P1040949_LEDdriverFlashing-1000.jpg
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-