Sperrschwinger

1,228,945. Blocking oscillator; automatic frequency control. NAUCHNO - ISSLEDOVATELSKY INSTITUT CHASOVOI PROMYSHLENNOSTI. 2 Oct., 1968, No. 46692/68. Headings H3A and H3T. A blocking oscillator includes a transistor 1 controlled by a secondary winding 2 of a transformer whose primary 3 is connected in series with a diode 4 across a diagonal of a bridge which includes as one branch a frequency determining RC network 5, 7. The second branch of the bridge may consist of resistors 8, 9, to the junction b of which a diode 11 is connected which with a current determining resistor 12 compensates for the transistor 1 temperature variations. Upon initial switch-on the capacitor 7 at first reverse biases the diode 4 due to its positive potential relative to point b, and when it has charged towards the negative voltage sufficiently to forward bias the diode 4, the winding 3 carries current. This causes a secondary voltage to develop and switch on the transistor 1, whose collector rises to produce the leading edge of a pulse, the top of which is maintained until the capacitor 7 is discharged, whereupon the initial conditions are reattained. In a modification (Fig. 2, not shown) the second branch of the bridge is a second RC network (15, 14) and the transistor collector is connected to the negative junction (c) of the two branches, a resistor (16) being connected between this and the negative end of the supply. A synchronizing circuit (Fig. 3, not shown) has a circuit (20) which senses the amount by which the frequency of, for example, a clock controlled by the blocking oscillator, is greater than that of a standard frequency source, and causes a switch (19) to close so that a capacitor (17) is charged from a source (13) for a time, and therefore to a voltage, dependent upon the difference. This voltage is applied through a resistor (18) across the resistor 9 of Fig. 1 (15, Fig. 2) to increase the period between pulses, and hence to decrease the oscillator frequency.