Help Deriving a Circuit

The circuit in #16 is purely a LED flasher. Why increase the supply voltage, then reduce it via a buck inverter? The design makes absolutely no sense at all.

Several people suggested that I look into the BuckPuck as a better and more efficient way to power the high power LEDs. That is why I thought it would be a good option. I know that the great majority of folks here are far more experienced than I am so I may not be seeing everything. However, for my own benefit (and perhaps others reading this post in the future) I do not want to be so quick to waive off any design. Particularly one that seems someone spent some time working on.

I do know that post #16 is in its current design just a flasher, and not alternating as I'd like. But I believe this could be modified. Collin55, thank you for clarifying the confusion about the design in number post #7. Would also appreciate hearing your thoughts to modify the design for this project (alternating 2x/3x flash, variable flash rate, four 3W LED groups, powered by cigarette lights).

Thanks to everyone.

eight 3W LEDS
Put 3 x 3watt in series = 6 LEDs Dont use the other two.
Approx 1amp per string. Use a BDxxx power transistor and one of the 555 circuits and a small current limit resistor.
The 555's may not be synchronised but who cares when they are flashing at such a high rate.

Thanks Colin. Just to clarify- are these modifications to the circuit from #7? Or a totally new circuit?

Also found another circuit just to add to this thread; Source . I recreated the circuit (seen below) because the original was poor resolution: **broken link removed**

The author of that circuit notes that it flashes 3x and alternates. In my simulation it flashed 3x on the Left but 2x on the right. This also seemed the case from the demonstration video: Link.

Also Found somebody using aluminum blocks as a heat sink here: **broken link removed**

You circuit has a mistake. You can remove the diodes and use just 10k resistors. You will need Darlington transistors.

colin55 said:

You circuit has a mistake. You can remove the diodes and use just 10k resistors. You will need Darlington transistors.

Click to expand...

I just copied it from the original: **broken link removed**

colin55 said:

You circuit has a mistake. You can remove the diodes and use just 10k resistors. You will need Darlington transistors.

Click to expand...

Colin,
You have not allowed for the 470R's from the transistor bases to 0V, with 10K to 9Vouts, the transistors will not switch on.

with 10K to 9Vouts, the transistors will not switch on.

Click to expand...

What rubbish.

I just copied it from the original:

Click to expand...

Your circuit has a mistake.

colin55 said:

What rubbish.

Click to expand...

A simple diagram which I hope even you can understand.

Look at the Base voltage due to replacing the diodes with 10K resistors, its ONLY 0.4V, so how will the transistor be switched ON.???

You really should think about the advice you give to OP's before posting.

EDIT:
Changing to Darlingtons would not help, IF the 470R's are left in place,,, they need to be increased in value.

My opinion, you do not need a buck puck. The buck puck shown in the design you dug up was for a battery powered circuit. It was designed (and performed well) in using every bit of power the batteries had before fading out. The OP of that thread was very happy with the design. Buck pucks tend to use power extremely efficiently, but if this is off a automotive circuit the need is dramatically reduced. Even at its most wasteful the car will handle LEDs easily.

If all you want is an alternate flasher, which I am coming to believe is what you want, then simple conventional MOSFETs would work well. They are cheap, reliable, and need very few extra parts.

So I am asking flat out, are you only wanting to alternate between two banks of LEDs (I assume at ½ second intervals)? If so I can sketch up a simple schematic.

Where you are going to have to pay attention is an area I probably can't help with, the mechanics of the design. This is not a big deal, as I suspect you have a firm idea as to what you want. Just remember what I have said about heat sinks.

If you plan on leaving this circuit on the dash or back then you probably ought to use some mil spec parts, as the temperatures this will see are going to be brutal. The more out of the sun (say between the sun visors) the happier the electronics will be. The main components I worry about are the capacitors, the rest are pretty heavy duty.

KISS (Keep It Simple Stupid) is a good rule of thumb for a project like this.

Rereading the post I have to ask if you want the circuit shown on post #24?

You can remove the diodes and use just 10k resistors.

Click to expand...

Dont you need the diodes to isolate the outputs of the 4017?

Of course you remove the 470R resistors as well. You use the voltage-division of the three 10k resistors to turn on the transistor.

colin55 said:

Of course you remove the 470R resistors as well. You use the voltage-division of the three 10k resistors to turn on the transistor.

Click to expand...

Why didn't you tell the OP this in your post.???

Instead of 'rubbishing' my post.?

I'd just leave in the diodes and the 470R resistors. It would work better that way.

If the O.P. just wants an alternating flasher, my nomination for simplest circuit would be a simple 2-transistor astable multivibrator driving MOSFETs (as suggested in post #31). Maybe not the absolute minimum parts count, but easy to build out of parts available everywhere. Frequency can be tweaked by R/C selection.

^^^^^- he wants 3 flashes from one string(left or right) and then 3 flashes from the other string, then repeat. Many of the circuits suggested dont' do that.

So how do you get 3 sequential flashes? a counter chip? or some easier way?

You could still use an astable multivibrator: have it trigger the 3-flashes-circuit. (You'd need one of them for each side.)

So you'd have:

• Multivibrator (2 transistors, a few passives)
• 2 counter chips
• 2 MOSFET switches

Still sounds pretty simple.

To answer your question, if you look over the thread, there are some curcuits which will give 3 flashes and some which will not. Of course it's simle, but the OP isn't experienced in simple electronics, and I'm afraid, his question has been misunderstood by some members who are trying to help.

OK how about two timers.
One to set the flash rate and one to select Left or Right.

This one uses 3 555s;
https://electronic-circuit-diagram.blogspot.com/2009/03/alternating-flasher-circuit-diagram.html

But I still think you can do it with two.

Andy