Driving the signals of two 4017's and providing operating power to them are two very different things.Does anyone know if a 555 chip can power two 4017 decade counters in parallel?
Sorry. I meant clock--not power.Driving the signals of two 4017's and providing operating power to them are two very different things.
S.c.h.e.m.a.t.i.c . . .
ak
Really - ? The word "Circuits" is right there in the title.I initially didn't include a schematic because I didn't see the need.
Hello. Thank you for your response. I meant for the 4017's white 3V 20mA leds to split the 30 mA between the two in parallel. I've read that the 4017 can source only 25mA of current but cannot find that in the datasheet. This 25 mA is still enough for my led's purposes. The 555 is adjusted so the flash rate somewhat matches the model of the Galactica. All leds share the 270-ohm resistor for each flash. I don't understand how the leds should be protected from reverse breakdown if they are susceptible to that. The power supply is regulated AC adapter so I don't understand the purpose of decoupling capacitors.Really - ? The word "Circuits" is right there in the title.
There are several errors in the schematic.
R6 is in series with the U3 GND connection. The chip will not function reliably.
There is no current limiting for the lower left group of LEDs.
There are several places where you have two LEDs in direct parallel. This does not work well, because no two devices are perfectly matched. You always will have one device hogging current away from the other to some degree. One way around this is to connect each pair of LEDs in series. This might work, but we do not have any information about the LEDs you are using. Please post the datasheet.
Because the circuit is powered by 12 V, there is around 10 V of reverse bias across the off LEDs. The reverse breakdown voltage varies depending on the part, but it usually is less than this. This can damage these parts because the current through them has no current limiting resistor in series. White and blue LEDs are particularly delicate in this regard.
The 4017 does not care about the input clock pulse width or duty cycle, so having D1 in there to make a narrow output pulse is not needed.
Your circuit requires that the CD4017 outputs supply over 30 mA to the LEDs. As stated in the datasheet, this is way above its rated output current.
Add decoupling capacitors across each chip's power pins.
And - the two 4017 circuits appear to be identical. If this is the intent, you would be better off to have only one 4017, and add driver transistors to its outputs to handle the LED current. A common part for this is a ULN2004. It has 7 darlington transistor driver stages capable of 500 mA.
ak
Where does it say 25mA? I'm a newbie to datasheets in every way.Don't see how anyone could say that.
View attachment 256558
View attachment 256559
View attachment 256560
If you allow the output voltage to drop below the test conditions, you're not operating the counter as intended and maximum current isn't characterized.
His point is that it does not. Not even close. It says that when operating on 12 V, the typical output current will be something between 0.9 mA and 3.5 mA.Where does it say 25mA? I'm a newbie to datasheets in every way.
Took a minute to find it.I initially didn't include a schematic because I didn't see the need.
My point is that it doesn't. In the CD4xxx family, the only devices that come close to that are CD4049, CD4050, and maybe 7 segment decoders.Where does it say 25mA? I'm a newbie to datasheets in every way.
I've read that the 4017 can source only 25mA of current but cannot find that in the datasheet.
At 17 ma that's closer to 141 ohm resistor.3V white LEDs in series and in series with at least a 27 ohms resistor.
by Jake Hertz
by Duane Benson
by Aaron Carman