Led driver circuit for automobile tail/brake light

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aravindhoysala

Joined Aug 6, 2008
31
Does any one got the circuit for above said application
i want to use single led for both state(for tail and brake )
 

mik3

Joined Feb 4, 2008
4,846
Does any one got the circuit for above said application
i want to use single led for both state(for tail and brake )
If the car has already a switched installed which senses when the brakes are pushed then connect the led in series with a proper value resistor on this switch (check if voltage is present on the switch). Otherwise you have to install a switch to sense when the brakes are pressed.
 

AllVol

Joined Nov 22, 2005
55
Be very careful what you change here. Remember, you are dealing with safety issues, not only your own, but others.
 

SgtWookie

Joined Jul 17, 2007
22,201
Does any one got the circuit for above said application
i want to use single led for both state(for tail and brake )
What is the manufacturer and part number of the LED?

It is not likely that a single LED will provide enough light.
 

Thread Starter

aravindhoysala

Joined Aug 6, 2008
31
LED RATINGS ARE
2V,30mA(SUPER BRIGHT RED LED) AND I WANT TO DESIGN FOR MY 2 WHEELER...:confused:
I WANT BOTH STATE FROM A SINGLE LED
i.e 8mA FOR TAIL AND 27mA FOR BRAKE INDICATION.
 

SgtWookie

Joined Jul 17, 2007
22,201
OK, I don't know what region you are living in.
In the USA, the Department of Transportation requires a RED-ORANGE light to be used (about 620-626nM wavelength).

Additionally, your LED should have a rather wide viewing angle; around 70°. Standard super-bright LEDs tend to have a rather narrow viewing angle.

Suitable for consideration would be HPWT-MH00 and HPWT-DH00 Phillips Superflux LumiLEDs. These are extremely bright, and have a wide viewing angle. Typical ratings are 70mA @2.2v. You can obtain these LEDs rather inexpensively online. You should get at least six of them.

I do not recommend standard super-bright LEDs for your project due to safety issues. If standard super-bright LEDs were used, your tail/brake light would only be observable from someone directly behind you, and be practically invisible to drivers not directly behind you.

Once you obtain suitable LEDs such as I've mentioned, then let's work on your circuit. I do have one that will work, but it is for higher power LEDs.
 
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aravindhoysala

Joined Aug 6, 2008
31
I am from India

LED SPECS (OBTAINED FROM SELLER):
FORWARD VOLTAGE : 2.4-3V
FORWARD CURRENT :30mA MAX
Peak Wavelength in nm :630
VIEWING ANGLE :30°~40°
And it is used by traffic signals manufacturers (as said by seller)

in India 'RED' tail lamp are used, there are so many vehicles running on factory fitted red led tail lamp
more over Superflux LumiLEDs are not available here.

please help me :(
 

Audioguru

Joined Dec 20, 2007
11,251
Cars and motorcycles that use LEDs as tail lights have many very bright and wide angle LEDs, not just a single dim narrow angle LED.
 

SgtWookie

Joined Jul 17, 2007
22,201
See the attached circuit. The brake light switch represents the supply voltage from your brake light switch. The tail light represents the supply from your parking lamp switch. When just the tail light is on, the LEDs will get about 8.2mA. When the brake switch is on, the LEDs will get about 28mA.

You should probably run at least 2 copies of the circuit for at least 8 LEDs; better to run three copies. One set pointing straight back, one set aimed about 30° to the left, one set aimed about 30° to the right.

The 1N5817 diodes are 30v 1A Schottky types. You can substitute other low voltage Schottkys if you can't find the 1N5817 available.

If you don't have 2N3906 transistors available, you could use BC556/BC557/BC558, BC327/BC328, or similar.
 

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Thread Starter

aravindhoysala

Joined Aug 6, 2008
31
FIRST OF ALL THANKS.
WILL THE CIRCUIT GIVE CONSTANT CURRENT? BECAUSE TAIL LAMP HOUSING WILL BE SEALED ,OPENING FOR REPLACING BAD LED 'S WOULD BE DIFFICULT.:rolleyes:
PLEASE MENTION THE PACKAGE FOR TRANSISTOR AND WATTAGE FOR RESISTOR .
90 OHMS IS NOT AVAILABLE,NEAREST VALUE IS 100 OHMS?:confused: PLEASE SUGGEST.

PLEASE TELL ME THE CIRCUITS POWER, BECAUSE PCB WILL BE HOUSED INSIDE TAIL LAMP,IF IT DISSIPATES MORE HEAT I HAVE TO INSTALL IT OUT SIDE.
THANKS TO ALL........:):):)
 

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SgtWookie

Joined Jul 17, 2007
22,201
PLEASE MENTION THE PACKAGE FOR TRANSISTOR AND WATTAGE FOR RESISTOR.
The transistor packages are TO-92; small 3-legged critters.
You can use 1/4 Watt resistors, or 1/2 Watt.
90 OHMS IS NOT AVAILABLE,NEAREST VALUE IS 100 OHMS?:confused: PLEASE SUGGEST.
Since I don't know what you have available, here is a list:
75 + 15 = 90
68 + 22 = 90
51 + 39 = 90
47 + 43 = 90
120 || 360 = 90
180 || 180 = 90
100 || 910 = 90.099
82 + 8.2 = 90.2
110 || 510 = 90.484
130 || 300 = 90.698
150 || 220 = 89.189
62 + 27 = 89
56 + 33 = 89
Example:
68 + 22 = 90 means wire them in series
120 || 360 = 90 means wire them in parallel.
PLEASE TELL ME THE CIRCUITS POWER, BECAUSE PCB WILL BE HOUSED INSIDE TAIL LAMP,IF IT DISSIPATES MORE HEAT I HAVE TO INSTALL IT OUT SIDE.
The formula for power is: P=EI, or Power in Watts = Voltage x Current.
Since V = 14 (worst case, maximum charge) and I = 0.03A per string, P=14x.0.03 = 0.42 Watts. If you build three strings, that is a total of 1.26 Watts.

I will guarantee you that is much less wattage than the original bulb.
An old standard 1157 bulb (tail/brake light) is 4W for the tail light, and 27W for the brake light.
 

Thread Starter

aravindhoysala

Joined Aug 6, 2008
31
two more doubts:
1.why we cannot use normal diode(i.e D5,D6,&D7)
2.WILL THE CIRCUIT GIVE CONSTANT CURRENT?:(
 

SgtWookie

Joined Jul 17, 2007
22,201
two more doubts:
1.why we cannot use normal diode(i.e D5,D6,&D7)
Because the low voltage drop across the Schottky diodes helps to keep the current very close whether the brake is applied with the tail light circuit ON or OFF.
If the tail lights are off, current is about 27mA
If the tail lights are on, current is about 29mA
If you changed to a different diode, the difference would be quite a bit larger.
2.WILL THE CIRCUIT GIVE CONSTANT CURRENT?
That is the whole idea of the circuit.
 

Audioguru

Joined Dec 20, 2007
11,251
The transistors are ordinary 2N3906. Look on their datasheet to see their TO-92 package.
91 ohms is a common 5% resistor value. if you use 100 ohms then the current in the LEDs will be lower and the LEDs will not be as bright.
It is easy to calculate power dissipation.
 

SgtWookie

Joined Jul 17, 2007
22,201
Audioguru,
Our OP is in India. I really have no idea as to what is available there. I've tried recommending several different transistors and a selection of resistors they might use.

I could guess for a long time and not arrive at a decent conclusion about what they might use out of what is available to them.

Asking the OP to put up a link to an Indian electronics store would not likely help very much, as I wouldn't be able to read it unless it was translated to English.

Our OP is obviously quite new to electronics, and rather unsure about things. I'm just trying to help them along as best I can.
 

Thread Starter

aravindhoysala

Joined Aug 6, 2008
31
thanks to Administrator/moderators who has created this useful forum .:)

special thanks to SgtWookie ,Audioguru ,mik3, AllVol.

NOW my next mission is to convert left/right turn indicator and head lamp to LED. please guide me


"The important thing is not to stop questioning." -Albert Einstein.

thanks a lot.......;)
 

SgtWookie

Joined Jul 17, 2007
22,201
Did someone steal all of your light bulbs? :confused:

In order to use LEDs for turn signals, the flasher unit would have to be replaced with something else, as the LEDs would not pass enough current to activate it.

If you want an LED headlight, buy one that is pre-made. Tail/brake lamps do not require precision alignment and focusing, where headlights do. The failure of a headlight while riding in the dark would be very likely to cause an accident. A headlight project really has too many safety implications to be undertaken by a hobbyist. Additionally, an LED capable of generating enough light to be used as a headlamp would require a great deal of power; just the LED alone would be quite expensive.
 
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Thread Starter

aravindhoysala

Joined Aug 6, 2008
31
why we require flasher ? because at indicator bulb point i am getting flasher output, inside indicator housing if we put constant current circuit with LED would be enough .
As for as head lamp is concerned it serves as standby (i will retain standard head lamp),
it would be helpful if give me constant current circuit along with formula to calculate resistors value with respect to LED's ratings

thank you
 
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