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.

led in car, reverse polarity protection ?

Status
Not open for further replies.

themikestar

New Member
i have been told that cars can generate a negitive voltage transient upto 400v, therfore led's in cars should always be protected my a diode becuase leds can usually only handle negitive voltages upto 5v. is this correct? and if so what would be a suitable surface mount replacement for a 1n4004 diode so i can save space, maybe a toshiba U1GC44 rectifier diode or a fairchild GF1A rectifier ?
 

Someone Electro

New Member
You mean is static.I one got a good shock wean i carid a box full of grocerys and i tocd the car(i amost dropt the box)
 

Exo

Active Member
themikestar said:
i have been told that cars can generate a negitive voltage transient upto 400v, therfore led's in cars should always be protected my a diode becuase leds can usually only handle negitive voltages upto 5v. is this correct? and if so what would be a suitable surface mount replacement for a 1n4004 diode so i can save space, maybe a toshiba U1GC44 rectifier diode or a fairchild GF1A rectifier ?

1N4001 - 1N4007 are available in SMD version. They look just the same (and equally big) as the normal version. Except they have no legs.
If you take a normal one, and cut off the legs real short it'll be almost the same
 

Roff

Well-Known Member
If you put the diode in series, it has to have high reverse breakdown voltage, and fast negative transients can still pass through it due to reverse recovery time and junction capacitance.
Put the diode in parallel with the LED (anode to cathode), and this all goes away. You can use almost any diode that can handle the impulse current (400v/Rlim, where Rlim is your series current limiting resistor). Reverse breakdown voltage is not an issue, because each diode protects the other from reverse breakdown.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top