Need help with an LED flasher circuit

[colin55]

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.

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

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

 

[The Guru]

My deepest apologies for everyone following this thread. I have been having some difficulties with my internet lately.
Everything is up and running again though.

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.

I made a direct measurement on the MOSFETs, and it turned out the second transistor in the ring is giving me measurements around 2V...
I suppose this is the big problem in this question. Should I try to put a lower-value resistor in parallel with the second LED chain?

 

[The Guru]

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?

I'm reading quite some contradicting ideas here... I should be trying a few things before settling on one...

Yes, I can try to run it at 6V. Let's hope I won't smoke any resistors. Quite possibly I might, as they'll be taking quite some punishment.
I will see though.

 

[The Guru]

Okay, I ran the little critter at 6V. Nothing worth noting happened.
I also performed another test on the second MOSFET's gate. It seems that the voltage on the gate is 3V relative to ground.
It's a bit hard to be exact, however, as my multimeter takes a second or more to settle, and the voltage on the gate decreases rather rapidly...

 

[gmphadte]

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

 

[The Guru]

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

Ah yes. But arr, ICs... I'm sorry but one of my main goals was to stay away from ICs and make something out of discrete components...
Thank you for your suggestion though! You are right, it would be far more versatile that way. If I really can't fix this circuit I will certainly give a method with ICs a thought.

I'd like to stick with discrete components for now though.