10 Watt high power LEDs.

Other Hardware LEDs and Multiplexing
1

I can't find a data sheet on those 10watt LEDs but...

10watt / 3 LED's (to give a share of each)
= 3.3watts per share (3 watts Red, Green, Blue).

3 watts at 12v
Roughly 0.25amps per RGB.

I'm well aware of the current limiter, the current is slightly too high for a UNL transistor array IC, too low for use of a mosfet, so to hell with it (I've got a 2n2222 for each segment 15 NPN's each heatsinked), I have in total 5 - 10watt LEDs, I decided to take a risk and not use any current limiting (Except on base), collector/emitter side and use a 1-5k resistor on the base to limit the current (eg, 2k for RED, 1k for Blue 800ohms for Green), which is all done, then I adjust the PWM to lower the current (for in the warmer months) and increase the current for colder months, i'll use an NTC thermistor or something as "reference" if it does not go to plan.

I'm not asking for help, just telling you what's going on...

What I can't decide on, these 10watt LEDs, there's 3 LED's in series (3 forward voltage drops), if each of these little LED's must be 1watt each, giving 3watts per channel., I have a 300watt heatsink along with all the transistors mounted on the heatsink along with the LEDs...

This may fail spectacularly after 30 minutes of 50watts of current draw lol... I have a large switching power supply raring to go... So here goes, one monster RGB LED chaser lol...

Either way i'll take pictures :slight_smile:

When done, I'll have it soldered up and I'll stick it outside somewhere.. (the pink LED in the background is barely drawing 80ma it's a 1watt LED) this LED bar (when running at full power) should make you see pretty stars for a while after viewing it....

20131022_164358[1].jpg

2

Hi, just looking at the pic, you may have to fit a fan to circulate air through the heatsink.

I looked at some LED lights for 240Vac application and they all had to have either some significantly finned heatsink and/or a cooling fan to keep their assemblies cool.

Tom.... :slight_smile:

3

As i see it... the heatsink will do just fine.

each 2n2222 can deliver up to 400ma of current (using the resistors on a 23c day)

15 * 0.4
6 Amps Total Delivery.
or 72 watts (before PWM)

With PWM i'll get a balance between 50-60watts

the power supply.... 240ac switch mode can supply 5amps at 12v (60watts)

So Fine line, and i'll be doing this with 2n2222's ! (all plastered to the heatsink)

4

Just curious: what are you making?

5

A 50 watt RGB led mood lamp (flood lamp) ....

And an arduino :slight_smile:

6

Here's the breadboard version and very dodgy connections, i'll ramp it up two - three x the power tomorrow when the paste fully sets.

7

Those LED-to-LED transitions are rather harsh and could be softened up some... it's a mood lamp. Try slower PWM changes and if you're feeling adventurous, write a routine that cycles through the LEDs, remembering where each one was during the last cycle, so they're all lit to some extent at the same time but dim and brighten them on some pattern or randomly.

8

You CANNOT lower the current draw using PWM. You limit the overall energy going into the LED, however, if the current exceeds that of the LEDs spec you may have already shortened the lifetime of the LEDs.

9

Headroom:
You CANNOT lower the current draw using PWM. You limit the overall energy going into the LED, however, if the current exceeds that of the LEDs spec you may have already shortened the lifetime of the LEDs.

You are kidding......... right?

You CAN lower the current draw via pwm (i do so all the time)

May have damaged?.. i wish i could get the current draw high enough to damage them due the pwm signal!

10

cjdelphi:

Headroom:
You CANNOT lower the current draw using PWM. You limit the overall energy going into the LED, however, if the current exceeds that of the LEDs spec you may have already shortened the lifetime of the LEDs.

You are kidding......... right?

You CAN lower the current draw via pwm (i do so all the time)

May have damaged?.. i wish i could get the current draw high enough to damage them due the pwm signal!

No, they are not kidding :slight_smile:

Unless you are using a Constant Current Driver with a PWM dimming capability, you can only reduce the average current not the peak current via PWM. If the peak current exceeds the recommended maximum of the LED then you will do some damage.

11

Magicj:

cjdelphi:

Headroom:
You CANNOT lower the current draw using PWM. You limit the overall energy going into the LED, however, if the current exceeds that of the LEDs spec you may have already shortened the lifetime of the LEDs.

You are kidding......... right?

You CAN lower the current draw via pwm (i do so all the time)

May have damaged?.. i wish i could get the current draw high enough to damage them due the pwm signal!

No, they are not kidding :slight_smile:

Unless you are using a Constant Current Driver with a PWM dimming capability, you can only reduce the average current not the peak current via PWM. If the peak current exceeds the recommended maximum of the LED then you will do some damage.

ughhhhh... for god sake! I have a limiting resistor on the base of each transistor!

  • I was being sarcastic.. you ARE kidding.

Even IF it "stopped" and got a constant hit with 5v.... the MAX current draw is 400ma (yes I've DONE IT, i have it wired up that way)

Now, stop with the bs please, I know what i'm doing here.....

12

If you are using current limiting resistors, then you will not damage the LEDs. However the assessment that with PWM you can perhaps reduce average current but not peak current is still correct.

13

Headroom:
If you are using current limiting resistors, then you will not damage the LEDs. However the assessment that with PWM you can perhaps reduce average current but not peak current is still correct.

I could not care less about controlling the current via PWM, as far as i'm concerned i'm trying to get as much current draw from PWM as possible.... I have everything heatsinked and works great, except I used a bad 74hc chip (never checked it first before soldering) the other half my circuit board works great :frowning:

14

I was merely pointing out that there was a technical inaccuracy in what you wrote and did want to point it out as it has been a misunderstand in more than one three/post on this forum. No reason to be defensive!

I am not sure I understand your problem not being able to draw enough current. You wrote in a post above that you are using current limiting resistors that will limit the current through the LEDs to 400mA. When you set the duty cycle of the PWM signal to 100% then the "switches" are on 100% of the time, thus you will draw these 400mA. If you want more current to flow you'd need to lower the value of the current limiting resistors, or is there something I am missing ?

15

I explained what i was doing...

The only current limiting is on the base. Got it now?

16

May I join too.

If Leds are on the collector and resistors are on the base, there is nothing to limit current to 400mA. Current is Base current * current gain. You need a resistor in series with the Leds.

and not use any current limiting (Except on base),

17

LMI:
May I join too.

If Leds are on the collector and resistors are on the base, there is nothing to limit current to 400mA. Current is Base current * current gain. You need a resistor in series with the Leds.

and not use any current limiting (Except on base),

There's nothing to limit the current?

The resistor on the base does! (Ugh)

18

cjdelphi:

LMI:
May I join too.

If Leds are on the collector and resistors are on the base, there is nothing to limit current to 400mA. Current is Base current * current gain. You need a resistor in series with the Leds.

and not use any current limiting (Except on base),

There's nothing to limit the current?

The resistor on the base does! (Ugh)

Perhaps. If you would show a schematic diagram of your circuit here. If not, that is all right too.

19

The resistor on the base does! (Ugh)

Have you calculated power dissipation in the transistor?

Without seeing a schematic I'm not exactly following what you are doing, but linearly controlling or current-limiting a 10W or 3W LED with a 2n2222 "feels like" you are going to fry the transistor. With 12 Volts, the current limiting resistor (or transistor) dissipates more power than the LED.

You can only (safely) pass the maximum-rated current through a transistor when it's in saturation (with nearly zero voltage across it). So, in a switching application (such as PWM), you CAN use the maximum current & voltage ratings. In linear applications, you need to consider power (Current x Voltage).

Also, the gain of the transistor tends to increase with heat. Without a feedback-control circuit you'll get more current through the transistor & LED as the temperature rises. Depending on where you are along the voltage/current curve, this can result in thermal runaway where more current = more heat = even more current = even more heat, until the transistor dies. (In other cases, you'll get more current but less voltage and everything will stabilize, or something else will limit the current, or something else will die first.)

20

It's like talking to the wall .....

The transistor is biased and heatsinked and working! Along with the leds thank you.