Quizz`Away

This time we present yet another problem covering elementary circuit design. The schematic shows an opamp circuit supplying a rectangular voltage with a frequency of about 34 kHz. As a remarkable aspect, components establishing positive feedback and normally required to create oscillation, are not available.

The oscillogram shows the voltages measured on the coil (U1, upper trace) and at the output (U2, lower trace). The photograph shows the circuit built in flying wire fashion. The oscillation frequency is so low that parasitic capacitances, inductances or stray coupling have no effect.

This month’s question to you all: