Believe it to be 2N2907 but not sure as the circuit diagram indicates only 2907. I am trying to simulate it with MultiSim version 8 and it's not in the database, yes I have googled it and didn't have much luck, wonder also how to update the MultiSim database with components that have come out since that version, can' afford the update as the entire package was given to me to play with.
Thanks, BTW, trying to make a little LED blinker that will last more than 24 hours on a 9V source, this circuit uses a 3v lithium cell 150mA-HR and indicates it should last 6 months. All the other circuits that I have built typically last about 24 hours then dead!
I'm amazed you can't find a model for the 2N2907. If you can find
2N2905, that will work fine, and 2N3906 is similar enough that it should work fine. Typical way to make a flasher that runs on a low- energy battery for a long time is to make the pulse width very short, so the duty cycle is low. For example, 10mA at 1000:1 duty cycle is
10uA, and that's 15000 hours with a 150mA-hr source, provided that you make the current during the "off" time really low. One common way to do it is to charge a capacitor through a high resistance, and when the voltage gets high enough, discharge it through the LED. However, there's a lot of energy wasted in the resistor and you can (at least theoretically) do even better if you use resonant charging through an inductor. National Semiconductor used to make an LED flasher IC that would run for a long time on a single 1.5V cell--LM3909. It wasn't all that low power, but still would flash an LED for a long time with an alkaline AA.
Google 'low current LED flasher' and you'll find LOTS of circuits.
R4 leads to about a constant 1uA draw (off time is basically 100%.) On-time is the LED plus R2 plus Q1's base drive [Q1's collector current additionally includes the discharge of C1 via Q2's base-emitter and R3 to Q1's collector, but that is paid for by the off time charging calculation] -- 15-20mA + 0.3mA + 0.5mA, or so. Mostly just the LED's current plus 1mA. Assume 20mA+1mA or 21mA. If that is truly 2ms out of 2s, that's 1:1000 and we're talking an averaged draw of 21uA.
What lithium battery are you using? The CR2025? Does the circuit actually seem to pulse at 2s intervals? Have you measured the pulse width itself with a scope? Is it also 2ms? (If much longer, that could account for some of the shorter life.) Did you check the magnitude of the current pulse through the LED? (Are you using a
47ohm for R1 above?)
Given the 20-50 ohm internal resistance of lithium button batteries, the draw from the battery is likely to be on the order of the "pulsed application" curve (7mA) which suggests you may need to degrade the
150mA-hr figure a little, as well. And you may see dimming over that estimated time, too.
I'd have guessed two months of use (double the pulse width and factor in a degraded spec for the battery), but probably not the 6 months as the PDF says. But not a day, either.
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Not easy to find these days, a PUT might be easier to get hold of - and if that's hard to find its easy to simulate with a complementary pair of transistors.
Something not a lot of people know - if you turn the PUT oscillator circuit upside down, you can do the same job with a small signal (TO92) thyristor like the 2N5061 or MCR102.
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