Transistor blocking oscillator stabilized against changes in bias voltage and temperature

摘要

A blocking oscillator for driving the armature of a buzzer comprises a transistor which is stabilized against changes in ambient temperature and fluctuations of a supply voltage. A core is provided for magnetically driving the armature, and carries thereon a drive coil which induces a regularly varying electromagnetic field therein as well as a control coil which is connected in feedback relationship with the drive coil. The drive coil forms together with the collector emitter path of the transistor a series circuit, which is connected with a power supply and which is shunted by another series circuit comprising a resistor, the control coil and a diode and which is also connected across the power supply. The base of the transistor is connected with the junction between the resistor and the control coil. The control coil is shunted by a forwardly poled diode. The diodes and the transistor are formed of a semiconductor material of the same kind so that their responses to changes in ambient temperature are similar to each other. In this manner, the diodes supply a bias voltage which varies with a change in the threshold voltage of the transistor as ambient temperature changes. The series combination of the diodes applies a bias voltage of substantially constant magnitude across the base and emitter of the transistor upon fluctuation of the supply voltage.