Power Multivibrator

This simple multivibrator circuit is remarkable for its high efficiency and ability to drive relatively heavy loads. The circuit supplies a symmetrical rec- tangular signal that floats with respect to the supply voltage. An astable multivibrator is formed by T5, Ts, Ri, R2, CI and C2. The collector currents of Ts and Ts drive Ti and T2 respectively, while the emitter currents drive T3 and T4 respectively. Current limiting may be dimensioned to requirement by chang- ing Ri. It should be noted, however, that the transistors may carry relatively high currents. Their current amplification, hFE, is, therefore, fairly low, so that the current limit point can be approximated with hmmax)(Ub -1.4)/Ri. With RI = 68 Q as shown in the circuit diagram, the multivibrator can be used for switching loads up to about 3 A. Output frequency of the oscillator is approximated by 0.7/(R2C), and is about 53 Hz with R2=68 kQ, C=C1=C2=220 nF and Ub=12 V (14 V: 50 Hz). One of the many applications of Ti ...