Led transistor driver circuit help!!!

[AGLite]

Hey guys,

Ok so I wired up a board with a 4049 and an 4066 ic chip! It pushes enough power to flash one side of thee led lights I made. But not enough... I know I have to wire in transistors!
The problem is I already made the lights and sealed them, so theres no taking them apart...Theres 36 leds per light and half is white and half is amber. To lights in all with a total of 72 leds. They are warning lights for my truck so they flash using the board I made. There is one power wire coming out of each light along with two grounds that hook up to the control/flasher board. I have to figure out a way to contain all the transistors in the project box with the board and only have two outputs. I dont even know if this will work and If it somehow will please try and find me a schematic. each out put must be able to power 36 leds I believe thats 4 transistors @ 200ma each. Thanks!!

INFO:
72 LEDs
12v
NPN TRANSISTORS 2N3904
720ma draw per light

 

[(*steve*)]

We'll need to see a circuit diagram because I have no idea why you would want to use a 4066, and the circuit diagram will tell me.

 

[AGLite]

Here you go!

Yeah btw I really hate this board It runs weird and its been having a ton of problems.
Please if you have a better circuit that runs off of 12v and has a quick flash pattern like this one(three quick flashes per side, alternating) and can handle a draw of 4 amps that would be great!!

 

[(*steve*)]

OK, yeah, you're using them as AND gates.

Connect the output of the 4066 to the gate of an N channel logic level mosfet and add a resistor (about 10k) to ground. Tie the sources to ground and place your load between whatever voltage is required and the drain of the mosfet.

A mosfet connected this way should be able to switch many amps. Ensure your load is current limited (i.e. don't just stick a high power LED there).

 

[AGLite]

okay so a few questions

1. What mosfet? 100v, 25v,30v? 10a,20a,5a?
2. resistor goes to ground and then ties into what? The gate?
3.How do I know its current limited? i have 36 leds they are wired in series in rows of 3 each with 150 ohm resistor, is that current limited?
4.for the last bit I connect the positive leg of the light(load) to my voltage and the negative to the drain ? correct?

 

[(*steve*)]

1) You need a logic level N channel mosfet capable of the current and voltage required by the load.

2) Yes, the gate.

3) if you can connect it to the voltage source and it doesn't emit smoke (or otherwise fail). A LED string with the appropriate resistor is OK.

4) yes.

The hardest part is (1) because you might not know how to do this.

Let me know something about the load (voltage and current) and I'll pick something for you. I'll suggest something from digikey.

Actually...

Go here.

then...

1) check the IN STOCK checkbox
2) under FET Type, select MOSFET N Channel Metal Oxide
3) under FET Feature select Logic Level gate
4) under voltage drain to source, select everything from 30 to 80 volts (click then shift-click)
5) under continuous current drain, select everything from 10 to 50A (click and shift-click)
6) under Mounting type, click through hole
7) click Apply Filters

8) Under package/case select anything that has TO-220 in it (it's easier to do this now)
9) click apply filters again.

10) go to the unit price column and click on the arrow pointing up (sort by price ascending)
11) enter the quantity required as 2
12) Click on sort by price - advanced

The cheapest options will now be on the first page. Select one and buy it from somewhere.

My recommendation is that you select one with a VGS(th) of 2.5V or less (yes, you could filter by that too)

 

[AGLite]

Is this Suitable?

http://search.digikey.com/us/en/products/IRLZ14PBF/IRLZ14PBF-ND/811728

If not My load voltage is 12v DC and it draws about 720ma! If you could pick a suitable one for me. Thanks!!

 

[(*steve*)]

It looks fine.

It allows a significant amount of overload, and can dissipate quite a bit of power even without a heatsink (maybe 1 or 2 watts) so it will cope even if your switching speed is poor.

And it's cheap.

 

[AGLite]

Ok they are ordered!! Thanks so much, you have been such a great help!

 

[(*steve*)]

Remember that these are static sensitive, so when you get them, handle them correctly.

Once they are in circuit (with a resistor from gate to source) they will be far harder to zap.

 

[CDRIVE]

Why does he need a 10K Gate to Gnd resistor? Wouldn't the existing 1K pullup resistors prevent the Gates from floating?

 

[(*steve*)]

The 1k resistor and the 2 LEDs disappear.

The gate is connected directly to the output of the 4066.

The problem with a pull-up resistor is that it would turn the mosfet on when the 4066 was open. That would not yield the correct flashing behaviour. A pull-down is required.

 

[CDRIVE]

I must have misinterpreted the data sheet on the 4066. I was under the impression that it was an open drain switch. Guess not. Thanks for correcting me... and yes, it would invert the logic.

 

[(*steve*)]

Yeah, it would make more sense here to use an AND gate -- which is effectively what this is doing.

As it's wired, it is kinda like a tristate buffer, but without the buffering.

 

[AGLite]

Ok it did not work!!!!!!!! Half the leds flash but not even at full brightness...

I think im am just gonna buy one or do you guys have a different circuit?

 

[(*steve*)]

Show us the circuit you have now and describe the problem more fully.

When you say half the LEDs flash, do you mean that the other half don't flash? Are they on or off?

You may have wired something incorrectly, or you may have misinterpreted something. The circuit diagram is the first critical piece.

Then we'll suggest some fault finding (probably initially manually turning the LEDs on and off) to ensure you're getting sufficient drive.

 

[CDRIVE]

Hey guys,

Ok so I wired up a board with a 4049 and an 4066 ic chip! It pushes enough power to flash one side of thee led lights I made. But not enough... I know I have to wire in transistors!
The problem is I already made the lights and sealed them, so theres no taking them apart...Theres 36 leds per light and half is white and half is amber. To lights in all with a total of 72 leds. <snip>
INFO:
72 LEDs
12v
NPN TRANSISTORS 2N3904
720ma draw per light

I re-read your first post and it leads me to believe that your LEDs are made up of those commercially made LED strips? If they are, they're made up of a series-parallel circuit. The series portion consists of 3 series LEDs and a limiting resistor. The parallel section repeats this to the end of the strip. I also re-read the data sheet on the 4066. It's a Bilateral Switch with no voltage output of its own. In your circuit the Gate voltages are derived from the output pins of the 4049 (flip flop), pins 10 & 12. You're circuit also appears to be a composite flash because pin2 of the 4049 is another flip-flop output that gates the 4066 on pins 5 & 13.

If your LEDs are a LED strip, as I believe it is, this is how it should be wired.

 

[junlee]

please let me have a look at the schematic and circuit board diagram