I could like to drive 4 high power LED in my car's headlight:

- Two Prolight Star 3W White in serial (each Vf 3.5v, 700ma)
- Two Prolight Star 3W Amber in serial (each Vf 2.2v, 700ma)

I got three inputs to determine what to turn on:
- DRL light (about 7.6v)
- Parking light (around 12 - 14v)
- Turn signal light (around 12 -14v)

The logic to determine whether white or amber LED series to be on is as following:
Amber = (Turn | DRL)
White = (Parking | DRL) & (! Turn)

As a software guy and noob on electronics, I kind of figured out that I need 4 NOR gates to get the desired logic result. But my questions are how should I make the whole thing work and using what kind of components.

For the NOR gates, I found the 74LS02 which give me 4 NOR gates, which seems prefect, but since the inputs are above 5v, I guess I will need to drop the input to 5v before feeding those input to the 75LS02, right? Will the NTE 977 (5V 100ma VR) works? I'm planning to have 3 of them to drop each input to 5V, feed those in to the logic, and at the same time combine all three lines to provide the 5V to the IC itself.

For the LED driver part, I'm planning to have two output pins from the 74LS02 connected to the base of two high power NPN (NTE 331), with a 12v source from car battery to collector, and the emitter connected to the some sort of 12v ready-made LED driver.

Does all this sounds good to go? Do I need additional components other than the 3x VR, 74LS02, and 2x NPN? Also, I would like to have the driver build into this circuit too, as the ready-made driver I have doesn't looks like very effecient.

Thanks for any help.

 

Here is the circuit I comes up with. Working? Do I need some additional cap or resistor?

 

Take a look at using 4000-series CMOS IC's instead of TTL-level logic. CMOS can run from up to 16v, which pretty much eliminates your need for all the voltage regulators.

A 4001 is a quad NOR gate.

 

Thanks. That simplify it a lot as I can remove the 3 diode too. I do have some questions tho. The NTE331 (or 2n6488) NPN I'm going to used as switch has a max emitter-base voltage as 5v, will the transistor be damaged if now I put a 12v to the base via the output pin from the 4001? BTW, will the current from 4001 output too low to even drive the NTE331?

 

You're currently using the 2N6488 as an emitter follower. In the original configuration, it wouldn't have worked very well; the emitter would've had an output of around 3.2v-3.9v depending upon load.

You could look at using a Darlington transistor. If you want to maintain the same logic as you have now, you'd need a PNP Darlington, like a TIP125 or 2N6040.

4000 series CMOS IC's don't source or sink much current. You'd need to use an 8.2k resistor between the CMOS output and the base of the Darlington to keep the current under 2mA.

 

Thanks, I'm really a noob on electronic and all your suggestions help a lot.

After searching a bit on web, I think most likely I will use the luxeon BuckPack for the LED driver. There is a sample schematic (http://www.leddynamics.com/LuxDrive/datasheets/3021-BuckPuck.pdf, Page 7 fig 13, 14) showing that it can be turn on/off with signal. Is that means I can just connect the output pin from 4001 directly without using the Darlington? Do I need to get back to use 74LS02 (plus all the 5v regulator) for the logic, or it will still work with 4001 for input/output ranged from 7v - 14v logic operation?

Oh BTW, do you know which approach is better? The first LED series consists of 2x white with total Vf = 7v, and the 2nd series has 2x Amber with total Vf = 4.4v, and the Buckpack said it need at least 2v + total Vf needed in the LED series to operate, with maximum 32v. I'm going to use seperate buckpack for white and amber. Should I drop to voltage to 9v first before I supply the power to the buckpack, or I can just power the buckpack with 12-14v directly from the car and let it handle the excess voltage? For the white it is about 5-7v difference, and the Amber one has about 8-10v difference, so I'm a little concern about that as the buckpack is kind of expansive ($15 each) and I don't want to replace it too often.

 

Saw you guys mentioned using Eagle for the schematic, so I give it a try.... kind of difficult to use but here is what it going to be look like. Will this work? The two grey box are the Luxeon Buckpack 3021-D-E-700, and I don't know how to put the GND and +12V link to the 4001 and the buckpack in the schematic, so they are missing from the diagram.