I want to convert a \$12V_{AC}\$ power supply output to use \$12V_{DC}\$ to power some outdoor LEDs.
The power supply as it stands will light the LEDs (with a slight flicker from the reverse polarity portion of the AC) but I have been told this may reduce the life of the LEDs having them reverse polarity for a long time.
So can someone suggest a simple rectifier circuit I could build or point me in the right direction of which one of these Maplin rectifiers is suitable (I'm not sure what the specifications refer to exactly)?
Answer
You may want to have a look at the answers to this question.
Applying AC to a LED is not a good idea. The flicker is not the main problem (may be hardly visible), but LEDs have a limited reverse voltage, usually about 5V. So the 12V you're using is way too high and may destroy your LED.
What you need is a rectifier, followed by a capacitor (to flatten out the rectified voltage). You can use a rectifier like in your Maplin link, or use discrete diodes.
1A diodes like 1N4001 are standard and will do nicely for a few standard LEDs. For the capacitor I use 2000uF/A as a rule of thumb, so if your LEDs consume 100mA you could use a 220uF/25V electrolytic capacitor. Be sure to place the capacitor correctly; it may explode if you reverse it.
The DC voltage will be about 15V (\$12V \times \sqrt{2} - 2V\$ ), so depending on the type of LED you're using it's a good idea to place a number of them in series, otherwise you'll have a big voltage drop over your series resistor = less efficient.
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