Free Project - 245 LED Display

[rele]

Hello members

This is not quite relate with this topic, but I thik it may be usefull.

I need to do increase power suply for led display to +7V - 9V instead +5V wich is now. Row drivers is irf9530 (from mcu thru 1K on gate, +5V sors, drainon led row), and column driver is HC164 + ULN2803.
Instead of irf9530 I try with BD242 (and few others), but if I increase suply on emiter above 5.5V, transistor is fully conductive (colector - emiter), and every led is on. With +5V on emiter everything is ok, but leds are with verry poor light.
When I replace ULN2803 with 8xBS170 (n-fet), I have little better result but still not good enough.
All this is without current limiter ressistors.

Leds are red, 2 leds in series for 1 dot.


Regards

[T.Jackson]

leds are current dependent, not voltage.

Trent Jackson

[rele]

Yes, but here I have two leds in series, and supply of +5V. I have voltage drop of 1.2-1.6 on ULN drivers, and rds on 9530 0.30 ohm. I guess I need to increase voltage?

Regards

Rele

[Ioannis]

Each led could use 2 volts so an increase is recommended.
Ioannis