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# Universal power supply for led

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#### siddarth.ghaste

Hi All,
I am making universal power supply for led by using 0.1uF/275V BOX capacitor and I am getting 20VAC and 6.5mA current at 230VAC. But below 110VAC I am not able to get good intensity.How to have constant current..... Is there any solution to this.PLEASE DO REPLY....

The reactance of your capacitor is :- 1/(2 X PI X F X C), for 50 HZ mains this is about 30K. The current it will provide is 230/30 mA = 7.3 mA and half this at 110V. You need to make the capacitor bigger. You have got a bridge rectifier across the LED, else you will blow the LED up (too much reverse voltage).
Frank

Points: 2

### siddarth.ghaste

Points: 2
Hi All,
I am making universal power supply for led by using 0.1uF/275V BOX capacitor and I am getting 20VAC and 6.5mA current at 230VAC. But below 110VAC I am not able to get good intensity.How to have constant current..... Is there any solution to this.PLEASE DO REPLY....

To make it UNIVERSAL you have to convert AC to DC and then (using something like PWM )ensure that the LED’s current remains almost constant ...
Simple solutions with just a capacitor and a diode + resistor won’t be universal …

:wink:
IanP

can I use 1uF/275V?

Take in mind that Blue LEDS are most sensitive to burn than Red ones, due to their greater energy required to stimulate eletrons.
Thus, you must take some care to avoid excessive ripple.

+++

siddarth.ghaste

### siddarth.ghaste

Points: 2
The current limiting for a 1 MF at 50 HZ = 70 mA. If you use a half wave rectifier then the current would be 35 mA. What is the current rating of your LED?
Frank

V
Points: 2
current rating of my led is 20mA. The problem is, How to maintain constant current?.....

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