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Step 12Haha! there's an even easier way!
I'm embarrassed to say i did not think of this method myself, i learned of it when i disassembled a flashlight that had a high brightnesss LED inside it.
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Put a PTC resistor (aka a "PTC resettable fuse") in series with your LED. wow. doesn't get easier than that.
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ok. Although simple, this method has some drawbacks:
- Your driving voltage can only be slightly higher than the LED "on" voltage. This is because PTC fuses are not designed for getting rid of a lot of heat so you need to keep the dropped voltage across the PTC fairly low. you can glue your ptc to a metal plate to help a bit.
- You won't be able to drive your LED at its maximum power. PTC fuses do not have a very accurate "trip" current. Typically they vary by a factor of 2 from the rated trip point. So, if you have a LED that needs 500mA, and you get a PTC rated at 500mA, you will end up with anywhere from 500mA to 1000mA - not safe for the LED. The only safe choice of PTC is a bit under-rated. Get the 250mA PTC, then your worst case is 500mA which the LED can handle.
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Example:
For a single LED rated about 3.4V and 500mA. Connect in series with a PTC rated about 250 mA. Driving voltage should be about 4.0V.
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Put a PTC resistor (aka a "PTC resettable fuse") in series with your LED. wow. doesn't get easier than that.
--------------
ok. Although simple, this method has some drawbacks:
- Your driving voltage can only be slightly higher than the LED "on" voltage. This is because PTC fuses are not designed for getting rid of a lot of heat so you need to keep the dropped voltage across the PTC fairly low. you can glue your ptc to a metal plate to help a bit.
- You won't be able to drive your LED at its maximum power. PTC fuses do not have a very accurate "trip" current. Typically they vary by a factor of 2 from the rated trip point. So, if you have a LED that needs 500mA, and you get a PTC rated at 500mA, you will end up with anywhere from 500mA to 1000mA - not safe for the LED. The only safe choice of PTC is a bit under-rated. Get the 250mA PTC, then your worst case is 500mA which the LED can handle.
-----------------
Example:
For a single LED rated about 3.4V and 500mA. Connect in series with a PTC rated about 250 mA. Driving voltage should be about 4.0V.
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I am building a constant power source driver for UV LEDs (4 nos) (High power 11W UV LEDs). The data sheets are as below.
http://www.ledengin.com/files/products/LZ4/LZ4-00U600.pdf
Could you please let me know if I can use your circuit for this.
Thanks in advance
Any key component with a set point that may vary by 100% is surely utterly useless.
You will not know untill you receive the PTC exactly what its trip point is.
The example shown raises more Q's than A's:
You may end up driving at the desired 500mA or the unwanted value of 250mA.
The circuit copied by the poster possibly employed this method but I'll bet the PTC 's were carefully sped'd & tested to be sure they were within an acceptable range, not something the hobbyist can easilty do!
In the battery pack of Laptop are Ptc used? You can take them?