I want to take 1.5 volts and boost it to 5 volts. Don't need a lot of power, maybe 100mW. Common mode chokes are cheap and readily available. Do people ever make blocking oscillators out of them? I'm looking at
-- That\'s not a common mode choke. http://www.murata.com/emc/knowhow/pdfs/te04ea-1/26to28e.pdf JF
Have done on a number of occasions.
I was a little hasty with digikey's parametric search. Anyway, would use a common mode choke or possibly a pulse transformer. Something like
Got any part numbers or links to chokes that might be appropriate for my power level?
Just a random common mode choke I harvested from a scrap monitor - the blocking oscillator is probably one of the simplest circuits you will ever build, almost any CM choke will work (even if only, after a fashion) small ones work best, aim for between 15 - 30 turns for each winding, so you might improve results by unwinding a few turns, I've always favoured the small toroid types.
Also aim for higher output voltage than you want and use a second transistor to shunt the B/E of the oscillator, the base of the shunt transistor is fed from the rectified O/P via a zener and small limiting resistor in series.
Yes, I built a blocking oscillator a while back and closed the loop the same way. Output voltage was swinging all over the place but a 0.1 uF cap across the base/collector junction of the second transistor stabilized everythng and then the circuit worked very well. I used it to double 12 volts to 24. Let the circuit run and it crapped after a day or so. Maybe the feedback winding had too many turns and resulted in excessive reverse voltage at the base of the blocking oscillator transistor. I might clamp the blocking transistor's b/e junction with a reverse parallel diode next time.
Yes, I built a blocking oscillator a while back and closed the loop the same way. Output voltage was swinging all over the place but a 0.1 uF cap across the base/collector junction of the second transistor stabilized everythng and then the circuit worked very well. I used it to double 12 volts to 24. Let the circuit run and it crapped after a day or so. Maybe the feedback winding had too many turns and resulted in excessive reverse voltage at the base of the blocking oscillator transistor. I might clamp the blocking transistor's b/e junction with a reverse parallel diode next time.
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