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Topic: Tons of breathing LEDs on single PWM pin (Read 1 time) previous topic - next topic


Did mike just say this.. You need resistors on the base of the transistors

Yes because I said that the LED and resistor had to be in the collector not the emitter, so when you make this change you need a resistor in the base.


Jan 13, 2013, 11:48 am Last Edit: Jan 13, 2013, 11:51 am by EVP Reason: 1
Oh, so if you don't change it and leave the led and resistor on the emitter it doesn't need a resistor on the base?
For some reason i thought they always needed a resistor on the base.


The configuration with the load in the emitter is called an emitter follower. The voltage on the emitter is 0.7V lower than on the base. You don't need a resistor to limit the current in this case because the emitter voltages rises as the transistor turns on and acts as negitave feedback preventing more current from being drawn.


What is a "breathing" led?

If you want to use one pwm bus to drive multiple fading, check into the driver design for Aura (?) led. The smartest I have seen.


If that is an N channel FET then it will not work.
Yo need a P type FET and base resistors and to put the LED and resistor in the collector of the transistor and not the emitter.

However when you have done all that you will still have trouble because the PWM signals will beat with each other, some work at diffrent frequencies so they will not add up like you hope they will.

Hmm. So, what would be a better solution? Hook each color up to a PWM output and tackle the software code?

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