Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Simple LED Questions

Status
Not open for further replies.

holabr

New Member
I am just starting to experiment a little with LEDs and have two projects in mind:

First, I have a white LED that is rated for 12V DC. I would like to use it as backlighting for a guage I am putting in my car. Since I intend to tie it into the dash light circuit to make it dimmable, what type of resistor can I use in series to prevent it from ever getting more than 12V. The voltage meter in the car shows voltages of 14 to 15 volts at times. The discription of the part says "... white LED with built-in resistors for 12Vdc, 12mA operation. No external resistor required. Works well on 4-12Vdc. Dimmer at lower voltages."

Second, I have some landscape lighting that is 12VAC. Since the light bulbs currently in the fixtures are standard wedge base type automotive bulbs, can I switch them to LED replacement bulbs. I know the LED replacement bulbs are intended for DC, will a diode in series solve the problem?

I know these are stupid simple questions for most of you, but I just recently learned how to program my VCR and now it is obsolete. Thanks.
 
For 12mA of current and a white LED drop of about 3.6V, the built-in resistor is 700Ω and drops about 8.4V . Use ohms law (R=V/I) to determine what addition resistance you need. (For example for 14V, the total required resistance would be (14-3.6)/12mA = 867Ω so you would add an external 160Ω resistor in series).

A single diode will only give half-wave rectification. Better would be a full-wave bridge (four rectifiers) which will give full wave rectification (the hockey puck type are easy to wire). You would only need one bridge for the whole sting of lights but you must observe proper polarity for all the lights.
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top