The design of transistor blocking oscillators

The basic circuit operation of the monostable transistor blocking oscillator using transformer inductance pulse-width control and a shunt load is described, and it is shown how this operation may be divided into phases convenient for analysis. The rise time and triggering are discussed. A formula for the pulse width is derived and a simple method of making this width accurate is given. It is shown how the recovery time may be calculated, and how the basic circuit may be modified to reduce the recovery time, thereby obtaining a space/mark ratio of the output pulses at least as low as unity if required, without exceeding the peak collector voltage of the transistor. An illustrative blocking-oscillator design is described and its measured output waveform given, enabling a comparison with the calculated output to be made.