Input = Two Eveready "C" Nimh cells, v=2.52 volts, i=116 mA. They
discharge at fairly stable voltage.
Output = Two Nichia white leds in parallel,
LED1: 3.46 volts, 24.8 mA,
LED2: 3.41 volts, 27.1 mA
I'm using an FP ferrite bead. Hole=.184", length=1/8", OD=3/8".
I don't know
what kind of ferrite it is. I got it from Hosfelt Electronics for 15 cents.
I have more test results for the two transistor circuit.
I swapped the NTE11 for an ECG128P. It started well but the output led
current dropped about in half. Then I switched to rechargable alkalines
instead of Nimh. I got a little more output current but it started harder.
I switched back to NTE11 / NTE12 and made a new coil with
about 40 turns
instead of 20. I got about 15 more mA through the leds so
I increased R2 to
5k to get 27 mA in each led.
Next I varied C2. With 47 micro F it almost doesn't run. I can
jump start it
but then it fades and goes out.
With C2=4.7 micro F it runs fine after a jump start by pulsing R2 to 3k.
Without C2 it starts perfectly.
C2=4.7 micro F
LED current = 27 mA each (3.5 v)
Battery input = 3 volts, 122 mA with C2=4.7, 116 mA with no C2.
Light quality = high
There's some kind of pattern emerging here. The 47 micro F
fine with the one transistor circuit, then for the two transistor
circuit, as the
number of coil turns increases, there's a preference for a lower
A larger coil might mean lower frequency so maybe lower
smaller C2 values. There's a little more light, but not much more,
with the 4.7
micro F C2 compared to no C2.
I guess I gotta go find a smaller C2 capacitor. What is another
size C1 to try?
Is there a size relationship between C1 and C2?
There isnt really any size relationship
between C1 and C2, except when ripple
is a concern.
For the purpose of understanding C1 a little better, Q2 has two
1. Q2 turned on
2. Q2 turned off
When Q2 is on, C1 charges very quickly though the base emitter of Q1
and through Q2 collector emitter.
When Q2 is off, C1 discharges through the 10k resistor.
At very low input voltages like 1.2 volts, R1=5k does appear to
work better then 10k.
A value of 500pf appears to work with inductor values from
200uH to 3200uH, but i would try 1000pf with larger inductances
also. Stick to 500pf or so for lower inductances.
Apparently, the lower the value of C1 the lower the ripple output.
I think I've got it.
It seems to be starting very well under all conditions. I think there is
relationship between C1 and C2.
Here's two things:
1. Sometimes my brain doesn't work very well. One of my capacitors,
the 4.7 micro F, is a polarized electrolytic. I tried hard, but for some of
my testing, I had it in backwards. Sorry.
2. It's starting right up now with C2 = 47 micro F. I put a second 680
pico F capacitor in parallel with the first C1. That gives it a little more
something that I've got to think about, but it's working. It starts right
#leds = 2
2 x 1.5 volt batteries
C1= two 680 pico F in parallel
C2= 47 micro F
Here's numbers for the two transistor circuit using a 47 micro F filter
capacitor on both the battery side and the LED side:
Two Alkaline batteries in series:
Vbattery = 3.06v
Ibattery = 114.7 mA
LED1: i=32.8 mA, v=3.58 volts
LED2: i=35.6 mA, v=3.54 volts
Two Nimh batteries in series:
Vbattery = 2.46v
Ibattery = 72.5 mA
LED1: i=18.5 mA, v=3.37 volts
LED2: i=16.6 mA, v=3.35 volts
Ibattery with and without the inlet filter capacitor was almost identical.