[VicPiMakers Projects] LED and Flourescent tube voltages

[George Bowden]

If anyone has some ideas on LED and fluorescent tubes, pile in.
I got some LED T8 tubes that are for direct replacement with
fluorescents connected to instant on ballasts.
I carefully looked up ballasts that are compatible to this LED tube
<https://www.gelighting.com/tubes-ballast-compatibility> and chose to look
at wiring diagrams for a B132IUNVHE-N ballast[image: image.png]
Clearly, the two pins at each end are joined together.

I then took apart one LED tube and drew its schematic. The electronics are
repeated at each end of the tube (drawn one above the other), which makes
sense because tubes can be inserted in either direction. I then drew AC
power connections per the diagram above. Pins 1 and 2 are at one end of the
tube, and pins 3 and 4 are at the other.  Given the shorting of pin1 to 2
and pin 3 to 4, capacitors 1,2,6,&7 are shorted out, as are resistors
1,2,3&4. Not shorted are the capacitors and diodes next to each other.
Tubes also could be inserted into ballast wiring where pin1 and pin2 are
not shorted, and it is interesting to have a tube design that must work
with 4 different power connections!!

[image: image.png]

Simulating this design in LTspice shows 70v peak across the bank of
leds, with current through each bank at 3.6 milliamps.
There are actually 3 banks connected in parallel of 22 leds connected in
series. I've only shown one bank.
I've guessed at the surface mount capacitor values, and the simulation does
not include the loads of LED bank2 and bank 3, so it is not quite
realistic.  Also, I am guessing at the LED type.
Given that ballasts try to maintain a certain current, using a 110v AC
input is probably wrong, but that is what I will use to power the tube.
I might include a 1.5uF 250v cap on the input to limit current, but the
simulated current through the LEDs is very low already...
My application is for a very weak light over my keyboard, so 3.6ma might be
fine.

[image: image.png]

Now to plug it in....AAGGGHHH

-- 
George Bowden  250-893-7423
Victoria BC
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