PWM setup

[BobK]

Note that the output of the driver is 20 to 42V. Your 4 LEDs probably require something like 12 to 16V. So it is putting out 20V, sensing too much current, and shutting down. Notice that it also says 7-12 LEDs, thus, you have less than the minimum. Why would you expect it to work when you are using it outside what it specifies?

Bob

 

[dave9]

Might have trouble regulating as it's spec'd for output of 7 to 12 LEDs, 20V to 42V while your 4 LEDs aren't dropping 20V across them.

 

[NeilMac]

That unit was recommended that why I got it, so basically add more LED's then. Each are 3W.
Thanks!

 

[Alec_t]

so basically add more LED's then. Each are 3W.

Then you would be exceeding the 12W power rating of the driver.

 

[NeilMac]

ok so you have to use 1W with 12 units.

 

[dave9]

Then you would be exceeding the 12W power rating of the driver.

It won't exceed the power rating because although the LEDs are rated up to 3W, the driver is 1W so ~ 330mA-ish.

That's how I'd do it too, under drive the LEDs for more efficiency and brightness per watt, plus easing the heatsink requirement by reducing per die thermal density, at least in a design where you don't need to wring the most light possible out of a single LED and highly focus it (flashlight, etc).

 

[NeilMac]

Thanks!
I ordered 1W LED's, hope they don't take two months .

 

[(*steve*)]

Then you would be exceeding the 12W power rating of the driver.

No it won't.

At whatever voltage they are, it will deliver the appropriate current to deliver 20W.

Actually, it's more likely it just delivers a constant current, but that's beside the point.

Thanks!
I ordered 1W LED's, hope they don't take two months

I'd add a few more 3W LEDs in the string until the voltage required increases to around 30V.

What is the forward voltage of the 1W and the 3W LEDs?

 

[NeilMac]

3.2 on the 1W, 2v on the 3W.

 

[Bluejets]

mmm...haven't seen 2v ..3w leds
Can you post a link to where you acquired them?

I have seen 9-12v...sure it's not that?

 

[dave9]

^ In the following post he mentioned 660nm red LEDs, which should be around 2.0Vf.
https://www.electronicspoint.com/threads/pwm-setup.289465/#post-1774462

 

[Alec_t]

No it won't.

Agreed. My bad.

 

[BobK]

Agree with @dave9, there is nothing wrong with running the 3W LEDs (if you use 7-12 of them in series) at 350mA.

Bob

 

[NeilMac]

mmm...haven't seen 2v ..3w leds
Can you post a link to where you acquired them?

I have seen 9-12v...sure it's not that?

https://www.pcboard.ca/high-power-led-3-watt.html

 

[NeilMac]

Got my 1W led's, still flashing but more erratic. So 12x1W still not balanced.
Got a couple other drivers so will experiment with them today.

 

[NeilMac]

Some success, the 3W are working with this new Driver, the 1W no, even tried another higher voltage driver and they still flashed.

 

[(*steve*)]

You absolutely must know the forward voltage of the LEDs, and then you must have enough in series so that the total forward voltage drop off in the range required by the driver.

If they are in the range of 1.5v to 2v then 4 or 5 n series should work with the driver that requires a load of 6v to 10v (if 4 didn't work, try 5).

In contrast, that driver with a minimum voltage of 20V may require between 10 and 14 of these same LEDs at minimum.

An easy way to measure the forward voltage is to get a 9V battery and a resistor between 100Ω and 1kΩ, and a multimeter. Connect a piece of wire to one terminal of the battery, and the resistor to the other. Power the LED from this. When the LED is glowing (it won't be bright) measure the voltage. Then make sure you have enough LEDs in series so that this voltage times the number of LEDs is not less than the minimum voltage (targetting a quarter to a third of the way into the voltage range would be a good starting point).

Tell us what the forward voltage is (it may differ between the different led types), the voltage range for the driver, and the number of LEDs you have in series.

Otherwise we cannot suggest anything more than "try more or less LEDs or a different driver".

 

[NeilMac]

3.2-3.4 forward V for the 1W leds

 

[(*steve*)]

Measured, or assumed?

 

[NeilMac]

Sellers website specs.
I still searching for a meter to replace my old one.