[VicPiMakers Projects] LED and Flourescent tube voltages

[Eileen]

Good detective work. 

Eileen 

Sent from my iPhone

> On May 9, 2022, at 10:47 AM, George Bowden <gtbowdeng at gmail.com> wrote:
> 
> 
> Well, I survived.  But these LED tubes need a ballast to produce a higher voltage than 110v.  The internal capacitors limit the current way too much.  Replacing the capacitors with a single 0.1 uF capacitor, for current limiting, allowed the dim output I desired.  But you have to get inside the bulb to do that, and the tube is made of glass...
> 
> 
> 
>> On Sun, May 8, 2022 at 11:30 AM George Bowden <gtbowdeng at gmail.com> wrote:
>> 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 and chose to look at wiring diagrams for a B132IUNVHE-N ballast
>> 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!!
>> 
>> 
>> 
>> 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.
>> 
>> 
>> 
>> Now to plug it in....AAGGGHHH
>> 
>> -- 
>> George Bowden  250-893-7423
>> Victoria BC
> 
> 
> -- 
> George Bowden  250-893-7423
> Victoria BC
> -- 
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