Talk:Blocking oscillator

Blocking Oscillator.
I wonder where the base current in this diagram comes from. Are we to suppose that the capacitor has some leakage current? Surely a time constant involving R and C would be appropriate here. Please comment on this somebody. --Technut 10:41, 28 September 2006 (UTC)

Base Current
The base current comes through a resistor which is not shown in this simplified schematic.

for monostable operation the resistor goes from the base to the emitter (and trigger input goes to the base) for astable operation the resistor goes to the centre tap of the transformer, or across the capacitor.

Jasen betts 22:13, 30 November 2007 (UTC)

Astable circuit as drawn won't start; also it can be achieved without use of a capacitor
(i) In general the circuit as drawn will not oscillate on its own; it needs some base current to get it going. Once "started" the astable circuit will oscillate without a base resistor, but it will not start unless there's a very special "glitch" on the power supply (robust enough to couple a +0.6 volt pulse to forward-bias the base).

(ii) If the capacitor is replaced by a resistor the circuit will oscillate as long as (i) the resistor is correctly chosen (e.g. 10K with windings in the 1 millihenry region of values), the orientation of the windings is correct, the voltage supply is greater than 0.6 volts (i.e. will bias the transistor "on"), the turns ratio is adequate to provide "blocking" of the supply voltage (i.e. 2:1 with 2 driving the base).

The analysis and subsequent equations are difficult. Core saturation, coupling, inductances, turns ratios, etc are all factors.


 * See Chapter 16 "Blocking-Oscillator Circuits" pages 597-621 and problem-pages 924-929 in
 * Jacob Millman and Herbert Taub, 1965, Pulse, Digital, and switching Waveforms: Devices and circuits for their generation and processing, McGraw-Hill Book Company, NY, LCCCN 64-66293.


 * See Chapter 7 "Circuits Containing Inductors or Transformers" pages 180-218 in particular 7-13 "The monostable blocking oscillator" p. 203ff, 7-14 "The astable blocking oscillator" p. 206ff in
 * Joseph Petit and Malcolm McWhorter, 1970, Electronic Switching, Timing, and Pulse Circuits: 2nd Edition, McGraw-Hill Book Company, NY, LCCCN: 78-114292.


 * For a tuned version of this, i.e. a circuit that will make pretty sinewaves if properly designed, see 17-17 "Resonant-Circuit Oscillators" pp. 530-532 in:
 * Jacob Millman and Christos Halkias, 1967, Electronic Devices and Circuits, McGraw-Hill Book Company, NY, ISBN 07-042380-6.

Millman and Taub observe that "As a matter of fact, the only essential difference between the tuned oscillator and the blocking oscillator is in the tightness of coupling between the transformer windings." (p. 616)

I will do some work on this article at some point or other. (I will need to review the analyses myself; they are non-trivial). Bill Wvbailey (talk) 16:35, 11 January 2010 (UTC)

Diagrams
A diagram that has just the listed blocking oscillator components of a resistor, transformer, and transistor, labeled to match the analysis abbreviations, would be helpful.

Currently there is a "base diagram" that does not include a resistor (although the resistor is in the analysis that is the bulk of this article) and a "joule thief" diagram that includes a capacitor (for an RC on the base of the transistor) and LED, which are not assumed in the main part of the analysis. Youblend2 (talk) 16:43, 22 October 2022 (UTC)