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Topic: PWM amplifier 9v or 12v (Read 2078 times) previous topic - next topic

thebfs

i have a program that output analog between 0 and 255 on with PWM stardard for arduino.
i need to use that signal. amplify it and  id like to use a 9v to drive it. but it has to go dim with low PWM and bright with high PWM.
i have some lm317's
or  uln2308 transistor arrrays handy
could i use the transitor array as a amp? if so could i see s schematic
id like to use what i have cause i dont have a lot of project cash.

Grumpy_Mike

I always think it is best if you amplify the PWM with a single transistor with the collector load to 9V. Then, only if you need to smooth it.
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

jwatte

What are you driving? Why do you need amplification? Do you need to drive a higher current load, or a higher voltage load, or both?
Personally, I use BS170 MOSFETs as low-end drivers unless there's a real reason to do anything else. Note that these do not "amplify" in the "multiplication" sense -- instead, they go "on" when the digital control pin is "ON," and vice versa, which matches what you want for a PWM signal.

thebfs

#3
Mar 18, 2012, 08:00 am Last Edit: Mar 18, 2012, 08:03 am by thebfs Reason: 1
i need to drive 2-3 1watt leds per arduino bin 2-3 now but may add 4-5 so from 6-15 1 watt leds brightness comtoled b PWM
led are 3-3.7 v i was hopeing to run them off 12v external pwr in sets of 3(series) gives 4 v but i have run these leds up to 6.5v and they hold out with heat sink.
so move voltage and current i guess. they need more than arduino can safely supply

Grumpy_Mike

So what limits the LED current? You need a constant current supply for high power LEDs.

thebfs

i was thinking to limit the 12v power source with something like thishttp://www.youtube.com/watch?v=2Rjlf7gnXms&annotation_id=annotation_313107&feature=iv so i dont have to make multiple drivers
wold something like that even work?
i just have resistors now. do they limit current or just voltage?
the project is going to be battery pwred so ienergy efficiency is a plus

Grumpy_Mike

Yes that will work but it is very wasteful of electric power. All the excess power gets turned into heat. You will need a heat sink attached to the regulator and that resistor needs to have a high enough rating to stand that current.

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