Go Down

Topic: PWM Led drivers which source current? (Read 1 time) previous topic - next topic

davivid

Are there any PWM LED drivers that source current in a similar way to the PWM outputs on the Arduino?

I need to drive 30 LEDs (10 RGB) on my LED driver boards (which are made, example below), and consist of a high current BJT switching circuit. Therefore I need to drive the base of the transistor with 0 - 5v.

All the IC's I have found are current sink. Any advice would be greatly appreciated!

johnwasser

If the current-sinking PWM driver you like has open-collector (or open-drain) outputs you can use pull-up resistors (to 5V) to turn those output into 5V logic outputs.  When the output is off the pull-up resistor will take the signal HIGH.  When the output is on it will pull the signal LOW.
Send Bitcoin tips to: 1L3CTDoTgrXNA5WyF77uWqt4gUdye9mezN
Send Litecoin tips to : LVtpaq6JgJAZwvnVq3ftVeHafWkcpmuR1e

retrolefty

Do you have a datasheet or link to that CCR2 device? Most constant current driver devices have active outputs and would not work the way you are attempting to PWM it.

Lefty

fungus

The thing labelled "CCR" on that diagram looks like a constant current regulator so you don't need any current regulation, all you need is PWM.

If so... put a PNP transistor where it says "7.5V" in your diagram and use a PWM chip to switch it, eg. TLC5940.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

davivid


If the current-sinking PWM driver you like has open-collector (or open-drain) outputs you can use pull-up resistors (to 5V) to turn those output into 5V logic outputs.  When the output is off the pull-up resistor will take the signal HIGH.  When the output is on it will pull the signal LOW.


That sounds like a great solution, how do I work out the optimum pull-up value?


Do you have a datasheet or link to that CCR2 device? Most constant current driver devices have active outputs and would not work the way you are attempting to PWM it.

Lefty


The circuit is taken from the figure 11 in the datasheet: http://www.onsemi.com/pub_link/Collateral/NSI50350AS-D.PDF

Go Up