led in car, reverse polarity protection ? - Electronic Circuits Projects Diagrams Free

themikestar · 2nd January 2004, 09:41 AM

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 · 2nd January 2004, 09:48 AM

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)

Someone Electro · 2nd January 2004, 09:49 AM

Ops Posted twice

ops:

My first time i posted twice.

Exo · 2nd January 2004, 12:43 PM

Quote:

Originally Posted by themikestar

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

themikestar · 2nd January 2004, 10:20 PM

would these do the job
http://www.fairchildsemi.com/ds/GF/GF1G.pdf

Roff · 2nd January 2004, 10:59 PM

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.

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2nd January 2004, 09:41 AM	(permalink)
themikestar	led in car, reverse polarity protection ? 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 ?

2nd January 2004, 09:48 AM	(permalink)
Someone Electro	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) __________________ Il give you shocking experience.

2nd January 2004, 09:49 AM	(permalink)
Someone Electro	Ops Posted twice ops: My first time i posted twice. __________________ Il give you shocking experience.

2nd January 2004, 10:20 PM	(permalink)
themikestar	would these do the job http://www.fairchildsemi.com/ds/GF/GF1G.pdf

2nd January 2004, 10:59 PM	(permalink)
Roff	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.