A single-transistor magnetic-coupled oscillator

AN IMPORTANT oscillator circuit which converts d-c to a-c square waves having an output frequency proportional to the d-c input voltage was developed by Royer.1 The circuit, shown in Fig. 1, employs a magnetic core constructed of square hysteresis loop material and two junction transistors operated as controlled switches.2 As the circuit oscillates, the core flux swings repetitively between its positive and negative saturation levels, ± ϕmax, the rate of flux excursion being proportional to the input voltage Ein. Thus, the frequency of oscillation is given by $f = {E_{in} \over 4N_{1 \phi \max}} \eqno{\hbox{(1)}}$ where N1 is the number of turns of the windings in the collector circuit. Since the flux saturation levels ϕmax vary with temperature, the output frequency is temperature-dependent. The output power is drawn from the input voltage source Ein, hence no power amplification is realized in this circuit.