Common cathode LED resistor with 4017 decade counter


Is it possible to use a common cathode resistor for all 10 LEDs with 4017 decade counter? I try it but only the first LED (output 0) lights up.

EDIT: I got it working. My wiring was wrong. I use a 9V battery power supply. I plan to cascade multiple 4017s (up to 10 of them) to a single LED sequence – so I may get 100 LEDs hooked to a single common resistor.

Best Answer

Yes you can, however it will subject the 'off' LEDs to reverse bias. If you are using a 5V supply or less, worst case will only be a few volts, which virtually all LEDS are rated for.

If you are using a CD4017 on an 18V supply, you will be exceeding the reverse rating of most LEDs-- typically 5V or so-- (but it might still work).

Each 'off' LED sees the output drive voltage (typically close to the supply voltage) minus the forward voltage of the 'on' LED (typically 2-3V, or maybe 1V if the LED is an IR type).