Led Diode Polarity

leds and inverse polarity, effects and prevention?

what happens to led if i connect them accidentally with inverse polarity?
i did, for a few seconds. but they are still working(luckily)
i though they would burn. maybe their life will be shorter now? input voltage is 19V

im thinking to add a 1n4007 diode to prevent future damage, from possible accidental connections.
how to connect it?

http://img19.imageshack.us/i/circuitodf.jpg/

that's a simplified schematic of my circuit. my real circuit has 270ohm resistor and 7 leds in each series
can i connect just one diode for all the parallels, or i need to connect one in every series of leds?
how much voltage takes?
thx
yeah i know the 19v /12v thing
that's just because i'm recycling an old laptop power source
max reverse current seems to be 10uA
i am supplying 25mA to the leds
i wonder why no harm was made

ideal diodes conduct electricty only in one direct. In reality, reversing the polarity of the voltage across the diode will cause a small leakage current to occur. This will not harm the diode. The real problem become when you exceed the reverse breakdown voltage of the diode. Once you do this it will start conducting and usually destroy the diode.

Special diode (zeners) are made to conduct at specific reverse voltages, but LEDs are generally not so precise. Read the datasheet for the LED to see how much reverse voltage it can withstand.

It sounds to me like you never exceeded the reverse breakdown voltage of your LEDs.

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Galaxy Audio Cricket Polarity Test Set $99.99 The Galaxy Audio battery-powered Cricket Polarity Test Set makes it easy to determine whether every component in an audio system is in or out of polarityfrom patch bay to console to speakers. The Cricket tests balanced and unbalanced cables of up to 2,000 feet in length. It will drive a stage snake (even one with transformers), and indicate which of a microphone's XLR connector pins is hot. The Cricket also plugs directly into a speaker cabinet and drives the components. A glance at the Galaxy Cricket's red and green LED's saves hours of troubleshooting. No wonder the Galaxy Audio Cricket polarity tester is indispensable tool for sound system owners, operators, installers and sound rental companies.Cricket Send Pulse GeneratorPulse Waveform Polarity: Positive-going balanced line output pulse switch selectable for hi or low level balanced signal with positive pressure produced at the tip of 1/4-inch jack and pin #2 of XLR jack.Speaker output pulse: Accepts 2 ohm (or greater) load with positive pressure produced at the tip of a 1/4-inch speaker jack and positive terminal of an internal speaker.Cricket Receive Pulse DetectorInternal microphone for testing speaker output.Polarity/Continuity Test: Female XLR pin 2,3,1 continuity; 1/4-inch jacks; tip, ring continuity. LEDs: Green indicates positive-going pulse polarity with power switch in "ON" position and battery status with power switch in "BAT" position. Red indicates negative-going pulse polarity. Detection inputs: one 1/4-inch, balanced; one XLR, balanced. Mic sensitivity; -64 dB, +/- 3dB

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About the Author

Sean Coppom is an employee at Polar-Ray, a Boulder, CO web-based business specializing in LED lighting solutions for residential and commercial customers.