Patent GB-1041262-A (GB)
Title: Oscillator
IPC: H02M7/5383
Filed: 1963-05-28
Abstract: 1,041,262. Multivibrators. GENERAL ELECTRIC CO. May 28, 1963 [Aug. 27, 1962 (2)], No. 21326/63. Heading H3T. A multivibrator comprises two solid-state devices (e.g. transistors, gate-controlled rectifiers) in series across a centre-tapped D.C. supply, the control electrodes of the devices being energized by separate transformer windings coupled to a third winding arranged between the common point of the devices and the centre-tap of the source, and switching between the alternate conductive states being initiated by the saturation of a second tranformer having windings connected to the energizing windings of the first transformer In Fig. 2 the primary winding 26 is coupled to secondaries 28, 30 which supply base drive alternately to transistors 20, 22 through two windings of a magnetic amplifier 46, 48; the control winding 44 is supplied with variable D.C. to control the multivibrator frequency; a number of control windings may be provided for alternative control by different signals. Resistors 36, 38 ensure reliable starting at low temperatures. The frequency depends also on the voltage of the D.C. supply 10, and thus by supplying the control winding 44 from this supply the frequency can be made independent of supply variations (Fig. 3, not shown). A temperature-sensitive resistor can be included in series for increased stability. In a modifica tion (Fig. 4, not shown), the right-hand halves of the windings 28, 30 are replaced by the secondary windings of a third transformer whose primary is energized by a source of synchronizing signals. The control winding 44 then varies the phase lag of the multivibrator relative to the synchronizing signals. In another version (Fig. 6, not shown) the windings of the magnetic amplifier are in parallel with the transformer secondaries instead of in series with them. The control winding is joined to a synchronizing source, or (Fig. 7, not shown) a D.C. supply for controlling the frequency. In a modification of this (Fig. 9, not shown), the magnetic amplifier is replaced by a two-winding saturable-core transformer. Inverters.-Two multivibrators of the above types can be coupled together to operate with a phase difference between one another, their differential output being a square wave. Thus in Fig. 5 two multivibrators of the type of Fig. 2 are coupled together by secondary windings 114, 116 which are on transformer 106 instead of 118. The differential output is applied across the primary of a saturable transformer 130 which provides an A.C. output. A portion of this output is rectified and applied to a bridge including a breakdown diode 150; the unbalance current of the bridge flows through the control winding 172 of a magnetic amplifier to vary the inductance of winding 170 and hence control the phase angle as in Fig. 4. Further control windings 86, 174 improve the stability as in Fig. 3. Inductor 138 and capacitor 136 are series resonant at the operating frequency and, together with capacitor 160, suppress harmonics. An inverter of this type may use the parallelconnected arrangement of Fig. 6 (Fig. 8, not shown). In another inverter (Fig. 10, not shown), two circuits of the type of Fig. 9 are coupled together as in Fig. 5 to supply a load directly (without transformer 130). Two pairs of diodes in series-parallel return power to the source when the load has a lagging power factor.