# Powering LED filaments (needing 50-60 V) with a joule thief/solar light thing?

Joined Sep 17, 2016
210
I would like to make the individual LED filaments in the below type of bulb flicker independently. Of course I will need to carefully remove the glass and break some of the connections so the filaments are powered independently. To generate the flickering signal, I would like to use flickering LEDs which have an integrated circuit inside the epoxy. I also want to use a PIR sensor to turn on the circuit.

It might be cool to be able to make my lamp battery powered (since it will only come on when movement is detected in a hallway) so the joule thief might let me do that. I know there are versions which let you get over 100 V from a single AA cell. I would use more than a single AA though and only need 50-60 V. It would be great if I could use one of those solar joule thief ICs but I don't think they would go up to 50 V. I might just make it mains powered though. Can you flicker a lamp through a relay like that? I think maybe not. Thanks for any input.

#### Dodgydave

Joined Jun 22, 2012
10,062
If you're going to use flickering leds, they use 3.3 to 5V without a series resistor and take 20/25 mA, so a 50 V supply will drive approx 11 leds.

Or use a 5V 2amp, supply and put them in Parallel.

#### Bernard

Joined Aug 7, 2008
5,788
What is the power rating of the bulb ?
Just speculation, 40 W / 4 = 10 W per string. 13 LEDs = .76 W / LED. or @ 3V = 250 mA/ LED. This will take a lot of battery or better an AC adapter.
Must run, will check back later.

#### Audioguru

Joined Dec 20, 2007
11,249
The IC in a solar garden light produces about 5V with no current or 3V with an output current of 10mA and a 1.2V battery current of 30mA.
If you want 60V at 10mA then the DC to DC converter input must be 60V x 10mA= 0.6W plus efficiency loss. If the battery is 7.2V (six Ni-MH in series?) then its current is about 100mA so 2300mAh AA cells will last for 23 hours with no flickering or maybe 46 hours with flickering.
A relay will wear out before the battery charge is gone.
How will you charge the battery?

Joined Sep 17, 2016
210
I dont want to run flickering LEDs in series (I think that would actually work really badly; if anything you'd run one in series with a bunch of regular LEDs but I want to use filaments) but rather use four flickering LEDs to control the rate of flicking of some LED filaments.

The wattage of the bulb is 4 W. This would be the maximum draw for all filaments on maximum brightness which would never be the case. Each filament takes about 15 mA at maximum brightness.

I think that the batteries (six NiMH in series) could be removed for charging (I have a charger which measures capacity so I'd make sure they were all very similar in capacity). Alternatively, I could use a couple of 18650 cells in series with a balancing charger module which connects to microUSB to charge. Do you think one of those solar IC modules would go up to 60 V? I guess a MOSFET works instead of a relay? Edit: actually, is a MOSFET even necessary? Perhaps a BC337-25 BJT would work just the same?

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#### Audioguru

Joined Dec 20, 2007
11,249
Your circuit with the transistor and the Mosfet is missing a resistor from the gate of the Mosfet to ground to turn it off and to allow the flickering LED to be powered because the gate draws no current and is a capacitor.

#### Bernard

Joined Aug 7, 2008
5,788
Did you count the number of LEDs in a string or is 13 a guess ?

#### Audioguru

Joined Dec 20, 2007
11,249
A yellow LED has a voltage of about 2.2V. Then with a current of only 40mA its power is only 2.2V x 40mA= 0.09W.

Your 2N2222 does not have enough base current for a collector current of 40mA. Its datasheet says that it saturates fairly well when its base current is 1/10th the collector current but yours has a base current of only about 1.3mA. If the 3300 ohm resistor value is reduced to 820 ohms then the 1W LED will be brighter and have a current of about 50mA (0.11W).

#### Bernard

Joined Aug 7, 2008
5,788
Strange things are afoot, first changes noted in brightness is when R2 goes from 10K to 15k & flickering decreases as R2 decreases from 1k to 470. Best operation at 2k2 to 3k3. The flickering LED does not put out
a pure PWM signal as it has some DC offset so 2N2222 is operating between a linear amplified & saturated switch. In another project, I stripped off the DC part with a comparator to load a shift register with pure highs & lows.
Each of the 4 LED strings has its own flicker & driver so only driving 15 to 20 mA each.

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#### Audioguru

Joined Dec 20, 2007
11,249
The transistor will completely turn off between "on" pulses if you add a base resistor to ground.