Electronic – Considerations for converting a LED Bulb from AC to DC power

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I was asked by my uncle to convert 22 units of gx53 LED Bulbs that are powered by 230VAC 5W to DC voltage power.

The LED Bulb itself consists of 5 LEDs(string) in series, in parallel to another 5 LEDs(string) in series.

I have disconnected the LEDs inside the Bulb from its inner driver and through a resistor i connected it to a DC power supply.

I learned using a measuring device(voltmeter) that each LED lights up with 8VDC and the current flowing through it is 8ma so the Bulb itself can be powered by 40VDC with current of 16~20ma.(5 * 8V=40V, 2 branches of LEDs * each branch is 8ma=16ma)

Now what i need is the right led driver.

I learned that LED drivers supply constant current while the output voltage is within a range of voltages.

So if i have 22 LED Bulbs that each need 20ma with 40VDC then the driver, to my understanding, should supply current of about 450ma with output voltage of at least 40VDC.

I ask for advice whether i'm right or wrong.

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Best Answer

Your calculation is incorrect. When you connect LEDs in series, the voltage required increases, but the current through the string is the same as for 1 LED. (The same electrons are flowing through all LEDs).

So if 1 led requires 8mA at ~8V, then 5 LEDs will require 8mA at ~40V.

Two of these strings in parallel would require 16mA at 40V (if your math for 1 led is correct).

An easy check you could have done is to calculate the wattage. 450mA at 40V would be 18W, where it should be around 5.

Your initial assumption of 8V and 8mA for 1 led would give a wattage per led of 64mW. So for all 10 leds we're looking at 0.64W, which is not correct. Again it should be around 5W.

You should hook up the driver again, and adjust it until 1 led is drawing 0.5W. Then redo the subsequent calculations with the current and voltage you measure.

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