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Basic Electronics » high side mosfet led multiplexing

May 14, 2010
by gnkarn
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Hi, I have a led matrix driven by TLCs5940 multiplexed in four layers, as the TLCs are constant current sinking devices, i need to use common anode rgb diodes with the cathodes connected to the TLC and the anodes wired together and multiplex in groups of 16.

My question is , do I need to use Pchannel mosfets to drive each layer and directly connect the gate to the layer driver ( 3 to 8 decoder)?, in this case what is the proper way to connect it?, 2) is there a way i could do the same with Nchannel Mosfet?,

Thankyou

June 06, 2010
by BobaMosfet
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You don't use FETs at all. You use the serial control protocol to control the TLC cascade. Reread the datasheet.

BM

June 07, 2010
by gnkarn
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Thankyou Boba, I have the circuit running now, Im using pchannel mosfets, and multiplexing the TLC on the high side in order to manage multiple leds with the same TLC channel and also have 3 TLCs for RGB , it is a way to use less circuits and keeping flexibility, I have an interrupt routine that takes care of this fast switching.

Gus

June 07, 2010
by BobaMosfet
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Okay, that's cool. Hmmm.... I'm interested in acquiring a few of those myself to see if my implemenation idea pans out. I think it can be done without FETs, but... maybe not.

Now you've got me all curious :P

BM

June 07, 2010
by gnkarn
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sure it can , it will be a mater of how many TLCs you will use, in order to drive 128 RGB leds , will use 3 TLCs ( cascaded one per color) multiplexed in 8 frames.

Doing with no multiplex, would need 24 TLCs.

Gus

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