LED Array Schematic Check?

[EasyGoing1]

Was wondering if someone would double-check my design here. It's relatively simple. I used an online LED array calculator to get the core array specs. And for the potentiometer, I figured that since the sum of the parallel resistors (since I don't know the internal resistance of the LEDs) is 5.5 Ohms, that adding a 5 ohm pot for dimming would be sufficient, if not overkill possibly.

Each LED is rated at 3.2V 150ma

VCC = 19V from a laptop power supply, so it should be a fairly stable source voltage.

I need the thing to be stable and to be able to dim it. Does this design seem like it would fit that requirement?



And here is the PCB layout, front and back....

[sam_sam_sam]

You could also use a PWM controller to dim the LEDs I have done this in the past you might need to use a filtering capacitor on the output so you do not see the switching of the PWM controller ( these controllers are very inexpensive to buy )

Because I also am going to use a LED yard light with a PWM controller to set to a certain brightness to save on battery power and not use a resistor to control them

Another option is use a switching power supply that can be adjustable voltage output I have a couple of them and they work pretty good and they are the same size as a laptop charger

[EasyGoing1]

Originally Posted by sam_sam_sam

You could also use a PWM controller to dim the LEDs I have done this in the past you might need to use a filtering capacitor on the output so you do not see the switching of the PWM controller

Because I also am going to use a LED yard light with a PWM controller to set to a certain brightness to save on battery power and not use a resistor to control them

Another option is use a switching power supply that can be adjustable voltage output I have a couple of them and they work pretty good and they are the same size as a laptop charger

You mean use something like this?

[EasyGoing1]

Originally Posted by sam_sam_sam

You could also use a PWM controller to dim the LEDs I have done this in the past you might need to use a filtering capacitor on the output so you do not see the switching of the PWM controller ( these controllers are very inexpensive to buy )

Lets say if I went with PWM for the source, and I wanted to add an RC filter to smooth out the PWM as in this schematic ... since the circuit is calculated to consume 11 watts, would that resistor (R5) need to be a 15 Watt resistor?

[diif]

You don't get flicker with those PWM controllers. I have the identical ones but bought from Ali at about the third of the price.

[sam_sam_sam]

Note you would not need R5 if used the PWM controller if you did it correctly you might need not need R1 to R4 you need to do some testing on the PWM controller that you use and see if those resistors are not need or you might less resistance values than what you have on your diagram now

[EasyGoing1]

Originally Posted by sam_sam_sam

Note you would not need R5 if used the PWM controller if you did it correctly you might need not need R1 to R4 you need to do some testing on the PWM controller that you use and see if those resistors are not need or you might less resistance values than what you have on your diagram now

I ordered one and got it today. Ive got some circuit boards from a past project configured in almost the same array, I can jurry rig it to be the same ... so ill be able to test the exact configuration.

No resistors at all, hu? That sounds risky.

[EasyGoing1]

Originally Posted by sam_sam_sam

Note you would not need R5 if used the PWM controller if you did it correctly you might need not need R1 to R4 you need to do some testing on the PWM controller that you use and see if those resistors are not need or you might less resistance values than what you have on your diagram now

So this is the unit I got, but when I connect power to it and turn it on, the led lights up but no voltage on the output. I verified the LED array is working with my bench power supply but this thing isn't doing shit.

[sam_sam_sam]

Are you sure that you do not have it hooked up backwards because I have done this myself before
I see that this board is marked the ones I have are not marked very well so it is to hook them up backwards

Yes this should work just make sure that you have a current meter hookup so that you do not over drive the LED array unless you want to change the brightness then you have a little bit more work to do then you need to find out what the resistance is on the pot ones you have reached the maximum current or less than the maximum current and that is allowed for the LED array then put a resistor on the top end of pot so that when the pot is maxed out this your maximum current you want to have on this LED array

I hope this helps you with what you want to do

[EasyGoing1]

Originally Posted by sam_sam_sam

Are you sure that you do not have it hooked up backwards because I have done this myself before
I see that this board is marked the ones I have are not marked very well so it is to hook them up backwards

Definitely had it hooked up properly ... I decided to tap all of the solder points that I could reach with my iron, and I got it to show me a voltage that was about ¾ of a volt lower than what the bench power supply was feeding it ... so if I gave it 12 volts, it would read about 11.25-ish on the output... but as soon as I hooked up the LEDs, i got nothin. So I decided to put the scope on it, and I got nothin that was useful in terms of a signal but the volt meter would read a voltage from the output but as soon as I connected the LEDs, I could get them to work VERY DIM when I cranked up the power supply to 30 volts feeding the PWM ...

Anyways ... it was basically a bust all around ... I decided to just order another one, assuming got a bad apple from the bunch ... and they're only like $6 ... people pay $15 for a pack of cigarettes these days ... no idea how people can afford to smoke. lol

[EasyGoing1]

Originally Posted by sam_sam_sam

Are you sure that you do not have it hooked up backwards because I have done this myself before
I see that this board is marked the ones I have are not marked very well so it is to hook them up backwards

So I got the new unit today from Amazon, and it worked right out of the gate ... and surprisingly it works quite well in spite of the fact that when I connect it to the scope, the signal is dirty as all hell. That was the first thing I connected it to and looking at that shitty signal I did not expect it to work at all ... but ... it does ... and amazingly well so I'll be using this for sure as the dimmer for my circuit. Though I'm leaving the series resistors in the circuit ... certainly can't hurt ... but I won't be using the resistor/pot that I originally asked about.

[sam_sam_sam]

See if you add a small value capacitor to the output make the power supply output cleaner and smoother

I have used this approach for a dc volt solenoid amplifier controller that I used to control a solenoid valve with a PWM controller because the machine controller went partially bad and I still need the machine to keep working with a partially malfunction machine controller

[EasyGoing1]

Originally Posted by sam_sam_sam

See if you add a small value capacitor to the output make the power supply output cleaner and smoother

Well, I already ordered the circuit board, but as luck would have it, I mirrored the VIN ports cause I wasn't sure which side of the board would make the most sense once I retro-fit the dimmer into the light enclosure... so whichever ports I don't use, will be perfect for a cap.

[sam_sam_sam]

Let us know how this works and if you can post a picture of it when it is finished

Oh by the way what is this made for

[EasyGoing1]

Originally Posted by sam_sam_sam

Let us know how this works and if you can post a picture of it when it is finished

Oh by the way what is this made for

I'd be happy to do that... what fun are projects if you can't show em off?

:-)

[EasyGoing1]

Originally Posted by sam_sam_sam

Let us know how this works and if you can post a picture of it when it is finished

Oh by the way what is this made for

Here is a pic of the final circuit board installed:





Should be obvious now what its for... it is replacing the stock circuit board on this lamp that I'v grown rather fond of over the years.

The PWM device is being fed 19 volts but only 17 are reaching the circuit at max volume ... I put a 1k µF cap on it for now cause that's what I had in the immediate vicinity... not impressed with the brightness but at only 17 volts that explains why. I think the PWM device has its own voltage drop that is possibly consuming that 2 volts so i gotta find a way to feed it like 21 volts or something so ˆ*can get 19 at the output.

[EasyGoing1]

So I realized my thinking was all wrong on the voltage issue... I didn't need to give it more voltage, I needed to give it less resistance. So I ran the numbers for a 17V source and the resistor value came back at 6.7-ish ... all I had in an SMD package was a 7 ohm ... PERFECT! So I replaced the resistors with the 7Ohm and the light is much brighter now and surprisingly does not put out a lot of heat which I am just elated about that. At max volume, you couldn't hold onto the LEDs for very long, but certainly not burning hot and at ½ to ¾ volume, they hardly get warm with plenty of usable light.

And here are photos looking through the magnifying glass, without the light on and then with the light on at full blast ... but the photos don't really do it justice.

[sam_sam_sam]

Nice work

I need to need to redo a fluorescent magnifying glass that is to heavy for the flex rod which is not long enough to begin with and use LED lights instead but I am not very good designing circuit boards

[eccerr0r]

The brightness should assist in depth of field in the camera - if it supports it.

Sigh. Unfortunately most cameras do not these days as it'd increase their thickness...

I'm still using fluorescent bulbs in my magnifier lamp and probably won't stop until they can't be had easily anymore. Though I should figure out why it seems to be sputtering filament onto the ends so quickly. I suppose it's a problem with running these tubes CC with its electronic ballast.

[EasyGoing1]

Originally Posted by eccerr0r

The brightness should assist in depth of field in the camera - if it supports it.

Sigh. Unfortunately most cameras do not these days as it'd increase their thickness...

I'm still using fluorescent bulbs in my magnifier lamp and probably won't stop until they can't be had easily anymore. Though I should figure out why it seems to be sputtering filament onto the ends so quickly. I suppose it's a problem with running these tubes CC with its electronic ballast.

I am NOT a fan of fluorescent light on any level ... I even replaced my kitchen lights with those LED tubes that they sell... I had to bypass the ballast entirely as the LED tubes only accept direct 110 but that was an easy thing to do and the light that they provide is AMAZING ... hands down superior to the fluorescent bulbs.