blueroomelectronics
Well-Known Member
Any thoughts on problems driving 4 LEDs on the 5V rail and 4 Relays on the 12V rail with the same ULN2803? (diode clamp on 12V rail)
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Move the LEDs to the 12v rail?
JimB
If you used the driver to switch low side it might work ok, the leds will see a reverse bias when the drive is 0ff (+12v - 5v, 7v) as long as they can stand this things should work, also you might be better putting a shottkey accross the coil as the back emf would reverse bias the led, the diode in the driver might not be quick enough esp including the inductance of the pcb track, causing high enough flyback to upset the led.
ChrisP58 said:Why would there ever be -7 Volts across the LEDs?
The ULN2803 is designed to be compatible with standard TTL families
while the ULN2804 is optimized for 6 to 15 volt high level CMOS or PMOS.
I'm using 3.3V logic if that makes any difference.