Drive led strips from 3.2 DAC

[TurBoss]

Hi

my first post

well the idea i have is that i need or i would to drive a led strip 12v single color from the A14 DAC, Is this posible ?

I'm not using pwm because this is to make the days longer for the birds and i think that they could see the leds flickering

thx

 

[Theremingenieur]

The DAC can not directly drive your led strip. You'd need a small voltage to current converter with an op amp and a transistor. The hugest problem would be thermal power dissipation. When driving the LED strip with continuous voltage/current instead of PWM, the transistor would have to eat up all the power which the LEDs don't need when dimmed and transform it into heat.

 

[Wozzy]

With the PWM set to 12 bits you can get 4096 steps at almost 12kHz.
I'm not sure that that would be noticeable, but you could use a capacitor could smooth that out somewhat.

Do not try to drive the LEDs directly from the Teensy as the current required would far exceed the maximum allowable for the pins.

Use an IRLZ44N MOSFET. It is a logic level device that can rapidly switch up to 20 amps when controlled directly by the Teensy's 3.3V PWM output.
See this LINK

 

[TurBoss]

thank you guys i'll switch to pwm

 

[PaulStoffregen]

You can use analogWriteFrequency() to control the PWM carrier frequency, if you're concerned about flicker.

But do be aware that really high frequencies require quite difficult design to get a high power transistor to switch so rapidly.

 

[TurBoss]

thx for the tip

Study says humans 60 Hz birds 100 Hz

so pwm wont be noticeable right ?

thx!

 

[Wozzy]

I can't speak for the birds, but I can't perceive any flashing beyond about 45 or 50 Hz.
I'm driving a 10 Watt white LED as a variable frequency and variable duration strobe light.

 

[PaulStoffregen]

so pwm wont be noticeable right ?

Well, if birds notice up to 100 Hz and you use the default 488 Hz, or crank it up into several thousand Hz, I'd say "probably not" noticeable.

 

[Ben]

About 60Hz is only true for non-moving applications. Even 100Hz may be visible if your eye does quick "scanning" movements across the LEDs (or the LEDs move), because that will leave an afterimage on your retina that consists of dots where the LEDs flashed ("Persistance of Vision"). I once drove a small 100mW laser with a PWM and I had to go beyond 500Hz so a rapid swipe across the room with the laser wouldn't make the PWMing apparent.

Ben