Circuit to control 5 LEDs

How to build an analog circuit to control 5 LEDs with a single input (0V-5V)?
the input will vary from 0V to 5V and i need help designing an analog LED multiplexing circuit for 5 LEDs such that the output will be:
1V Light 1 on
2V Light 2 on
3V Light 3 on
4V Light 4 on
5V Light 5 on
PS:I know this will be very easy using a micro but I dont want to use a micro

Only 1 LED needs to be on every time

If you mean something like 0-1V light 1 on, 1-2V light 2 on etc than you can do it using LM339s ... I think you can also do it exactly the same if you have narrower margins around the specified voltages). Also the output of the LM339 can drive (AFAIK) is open-collector so you can connect it to any external voltage.

You can look at the datasheet for the comparator here http://www.national.com/ds/LM/LM339.pdf and I bet you can figure out a schematic for your multiplexer.

Good luck!

You say only one LED needs to be on at a time, but is it OK if all the previous LEDs are on, like a bar graph? If so, I think that makes it easier.

You didn't say how accurate it needs to be. Suppose each LED is driven by a separate low side NPN transistor. These will require one silicon junction drop on the base to turn on, which is less than your 1V threshold. With a different voltage divider feeding each base, you can arrange the LEDs to come on at whatever threshold voltages you choose.

The thresholds will be a bit soft, especially for the higher ones, but you didn't specify if that matters.

I once did a very quick and dirty power supply verification circuit based on this principal for a production test. If the green LED lit but not the red one, the power supply output was OK. It worked very well for the purpose.

If you want more accuracy and can tolerate a little more complexity, then a separate comparator driving each LED as Dorin suggested is a good approach.

Here's another thought. You can use TL431 instead of NPN transistors if you can find any variants with 1V or less threshold voltage. You can think of a TL431 as being a NPN transistor with a accurate B-E drop. The ones I've seen have higher threshold voltages, but perhaps somebody out there makes a TL431-like device with a lower threshold voltage.

There are other Ic's like LB1405 which will give 5 LED output. TA7666 with 2 x 5 LED output etc.


Good luck!

I guess,YOu can use comperator instead of micro..may b

The LM3916 Dot/Bar Display Driver is an ideal solution.