Need help with an LED flasher circuit

I think you need to balance the load currents on all stages

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colin55 said:

You must make sure the voltage on the gate is sufficient to turn the FET on fully. If it is only partially turned on the LED will illuminate but the voltage across the FET will not be low enough to prvide a LOW for the following FET.
Measure the voltage across the FET to find this.


Not really. You need to turn each FET on fully to get the circuit to work.

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KJ6EAD said:

As mentioned by Colin in post #34, since the timing is controlled by the charge/discharge rate of the capacitors and the gate characteristics of the FETs (all the same) but is affected by the load (unique) via the interstage resistors (all the same) I think you need to balance the load currents on all stages by adding a resistor from drain to Vcc on the two lower current stages so all stages draw 240mA. Alternatively, you may be able to achieve even switching times by fine tuning the interstage resistances individually.

I'm also concerned that you may not have enough gate voltage to turn the FETs fully on. This is where I'd want an oscilloscope to observe the gate voltage versus time. Can you run the circuit on 6V?

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gmphadte said:

Another simple way using ICs---555 as an astable, CD 4017 and a transistor as driver for each output.
CD4017 has 10 decoded outputs, works from 3 volts to 15+ volts, u can select how many outputs u want by connecting reset to the appropriate output pin.

and u can play with it with dip switches in the output to get your individual overlapping, non overlapping, with gap ...sequences.

You can also extend the number of outputs by using multiple 4017 using some gates.

Gajanan Phadte

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