GB1349870A - Regulated electrical power supply - Google Patents

Abstract

1349870 Converting TEKTRONIX Inc 19 April 1971 [4 March 1970] 22901/71 Heading H2F [Also in Divisions G3 and H3] In a DC-DC converter, current from an input source 10 is periodically switched at 24 into a winding 20 of a linear transformer 22, the build up of current being monitored by a separate transformer 28 which is arranged to interrupt the current at 24 when it reaches a predetermined value. The output voltage is monitored at 64 and used to change the frequency of the pulses of current controlled at 24 so as to minimize variations in output voltage. As described, direct voltage which may vary between the limits 100-400V is derived from the mains 12 by a rectifier 10 and is periodically switched by a transistor 24 into the primary 20 of transformer 22. Transistor 24 is periodically turned on at a frequency determined by a triggered oscillator 72 synchronized to a voltage controlled oscillator 68. At the end of each pulse of current in winding 20, the resulting voltage induced in the secondaries 38 is rectified by diodes 40 and smoothed by capacitors 42 giving -4 kV at terminal 50. A voltage indicative of the output voltage is derived at 62 and compared at 64 with a battery or Zener diode (Fig. 3, not shown) and the resultant fed on line 66 (Fig. 2) to control the frequency of an oscillator 68 (20-30 kHz) using a programmable unijunction transistor 86. The pulses from 86 are fed via transistors 104, 130 and transformer 70 to synchronize a further oscillator 72 using a further programmable unijunction transistor 110, normally free-running at a much lower frequency. Pulses from oscillator 72 are fed on line 74 via a control circuit 26 (Fig. 3, not shown) to trigger the main switching transistor 24. Pulses induced in winding 84 of transformer 22 are added to the output of oscillator 72 so as to hold off conduction of transistor 24 while transformer 22 is still ringing. Fig. 5 (not shown) relates to a damper circuit comprising a diode bridge shunted by a transistor and connected across winding 82 of transformer 22 so as to damp out further oscillation. Fig. 6 (not shown) shows how the output voltage is made independent of input voltage by turning off transistor 24 each time the current reaches a predetermined value. Starting.-In Fig. 4 (not shown) a Darlington pair of transistors and Zener diode are used as a simple stabilizer to provide supply voltage for the oscillator 72 when the circuit is first switched on. This voltage is replaced by 50V derived by rectifying the output of winding 78 of transformer 22 when the system is operating correctly.