1. We will be in Read Only mode (no new threads, replies, registration) starting at 9:00 EDT for a number of hours as we migrate the forums to upgraded software.

# LED driver

Discussion in 'General Electronics Chat' started by JohnUK21, Dec 26, 2014.

1. ### JohnUK21 Thread Starter New Member

Dec 23, 2014
4
0
I want to replace the LED driver of a fitting that has a consumption of 15 w

They gave me a driver with an output of 23-28 V with 500mA constant current

This has an output of 11.5 to 14w. When I asked them if it is correct they said that the driver has a power factor of 0.9

And 14w/0.9=15.5w

So they declare the driver 15w

I'm confused . Please someone help!

2. ### MikeML AAC Fanatic!

Oct 2, 2009
5,444
1,075
What are the LED ratings?
LED Voltage?
LED current?

JohnUK21 likes this.
3. ### JohnUK21 Thread Starter New Member

Dec 23, 2014
4
0
Thank you mike!!

I have to check the led specs

However how is the power factor related and they declare the driver 15w?

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,444
1,075
Usually, it is the efficiency that matters; not the power factor...

#12 likes this.
5. ### #12 Expert

Nov 30, 2010
18,076
9,691
Sounds like, "Baffle them with BS". An LED is not a reactive load, so power factor has nothing to do with it.

PackratKing likes this.
6. ### ian field AAC Fanatic!

Oct 27, 2012
6,543
1,198
If you take power factor to indicate the difference between resistive & reactive loads, then you might get away with that.

A string of LEDs with a limiting resistor would only draw current when the sum total of Vfs were exceeded by near the peak half-cycle - this is pretty much what common usage takes PF to mean nowadays.

Similarly, a SMPSU only takes blips of current at the crests of the sinewave to replenish the charge on the reservoir capacitor.

AFAIK; anything over 50W must have a PFC front end - this is usually a boost converter, on the mains bridge rectifier; the reservoir cap is replaced by a much smaller foil cap as filtering, the current pulses drawn by the boost converter more or less track the instantaneous value of the mains sinewave.

The boost reg charges the reservoir electrolytic for the main SMPSU section - in a UK 220V unit the reservoir cap would typically be rated 450V.

#12 likes this.
7. ### #12 Expert

Nov 30, 2010
18,076
9,691
This thread seems to be about 15 watts, and if you try to use power factor to get there, you have me stumped. However, thanks for the information. I learn something almost every day here.

PackratKing likes this.