GB1421797A - Converters and circuitry therefor - Google Patents

Abstract

1421797 Automatic voltage control WESTERN ELECTRIC CO Inc 14 Aug 1973 [17 Aug 1972] 38469/73 Heading G3R [Also in Division H2] In or for a D.C.-D.C. converter, a circuit for balancing the currents in two switching devices 10, 20 so as to avoid saturation of the main transformer 30, comprises means 15, 16 for monitoring the currents in the respective switching devices 10, 20 and for providing a signal representative of the difference between said currents and means responsive to said difference signal for modifying the drive signals to the switching devices 10, 20 so as to equalize conduction in said devices. As described, transistors 10, 20 are driven into conduction alternately so as to connect a D.C. supply 1, 2 to alternate sides of the primary winding 31 of transformer 30. If the characteristics such as saturation voltage level, charge storage or delay times of the transistors are not matched, the transformer 30 could be driven into saturation. Signals representing the respective currents are developed across resistors 15, 16 and fed to terminals 101,102, Fig. 3, of a differential amplifier comprising transistors 110, 120, 210, 220 which provide an output across capacitor 207 indicative of the difference current. This output is added to a squarewave from multivibrator 300 and used to control the D.C. level of a triangular wave, Fig. 2, generated by integration at 202. The triangular wave is fed to the bases of transistors 410, 420 and compared with voltages at the bases of transistors 430, 440 which respectively represent the upper and lower thresholds 26, 27. Drive pulses for one of the transistors 10, 20 are derived from the collector of transistor 410 via transistor 450 during the time the triangular wave exceeds the upper threshold 26. Further pulses for the other main transistor 10, 20 are derived from the collector of transistor 420 via transistors 460, 470 when the triangular wave is below the level of the lower threshold 27. The position of the triangular wave relative to the two thresholds 26, 27 is automatically adjusted in response to the signal at the base of transistor 210 so as to equalize the currents in the main transistors 10, 20. Automatic Voltage Control. The D.C. output voltage is compared at 60 Fig. 1 with a reference (not shown) and the resulting error fed to the base of transistor 480 which controls the separation of the two thresholds 26, 27 and thus maintains the D.C. output voltage from the converter constant.