Just finished soldering my phased locked loop with a 4046, 40106, 4066 and hope to add some other cmos ICs. I want to add some blinky LEDS to my 4046,4093,40106,4017,4060 cmos chips etc. just worried about connecting my LEDs to the chips and harming the cmos. My 5mm green, yellow, blue, white are 3-3.2V and the orange and red ones are 2-2.2V. Will these harm my cmos chips. I’m getting some 470k resistors, so that should help. But would I need resistors if the LEDs are 3.2V? Also should I only connect these to the outputs of the cmos chips or ther outputs?
My past diy synth projects with 556 ICs with some other cmos ICs connected worked fine and so no problems when adding a resistor. Merry Christmas and a Happy New Year!
Look at the datasheets. For example, for the 40106, datasheet here: https://www.ti.com/lit/ds/symlink/cd40106b.pdf . On p. 8 it says with a 10 V supply at 25°C it can source 1.3 mA minimum, 2.6 mA typical. Not a huge current (LEDs typically can take up to around 20 mA) but probably enough.
I’d always use a resistor.
For instance, with a 10 V supply and an LED with 2 V forward voltage, you would drop 10-2=8 V across the resistor. To keep the current below 2 mA Ohm’s law says you need R = V/I = 8/.002 = 4k.
That’s if the output is only driving the LED; if it’s also connected to something else that’s drawing comparable amounts of current you’d have to account for that.
Without the resistor presumably the chip’s output current limit would mean the output voltage would sag down to whatever it would need to be on the LED’s I vs V curve. I doubt the chip would be damaged but the output voltage would not be what you’d expect. If the output is only driving the LED and nothing else then it’d probably be okay.
470k resistors? That’s very high. With 10 V supply and 2 V forward voltage that would give V/R = 8/470k = 17 µA current, even with a superbright LED I don’t think it’d light up much. 470R would be 17 mA current which would light up a standard LED brightly, but that’d be more current than the chip can be expected to supply.
If you need brighter LEDs or just to be cautious you can use transistors or op amps to buffer the outputs.
Hiya, Many thanks sor the quick reply and some amazing info! I did test with a 3.2v LED. 470k resistor connected from phase out on the 4046 IC then into the + of the LED then - of that LED into GND. Had this working from my 9v battery. I’m quite pleased with it. Obviously if I hooked up a new 9v battery it would be brighter. Will this still damage the IC, but what you’ve said it should be ok. So I could go ahead and connect some similar 3.2v leds to other outputs of my cmos ICs? I did a small film of my led but was unable to upload it to show, as it only accepts images? Many thanks