Patent GB-1343319-A (GB)
Title: Self-regulated dc to dc converter
IPC: H02M3/338
Filed: 1971-04-19
Abstract: 1343319 D.C. - D.C. converters GTE AUTOMATIC ELECTRIC LABORATORIES Inc 19 April 1971 [25 March 1970] 24983/71 Heading H2F [Also in Divisions G3 and H3] A self-regulated D.C.-D.C. converter comprises a pulse generator, the duration of pulses of which is controlled by a variable impedance (such as transistor 75) coupled via a diode bridge to a secondary winding 63 of a transformer 62 in the control circuit, in response to changes in converter output voltage and by a second variable impedance (such as transistor 76) coupled via second diode bridge to a further secondary winding 64 of transformer 62 in response to the converter being subjected to excessive electrical conditions. Transformer 62 provides D.C. isolation between converter input, output and control circuits. As described, the D.C. input is filtered at F1 and fed to an inverter IP of the type arranged to provide a waveform of the form shown in Fig. 2 where the pulse duration To is automatically controlled so as to maintain constant output voltage. The output of inverter IP is rectified by a bridge 41 ... 44 and a resulting D.C. smoothed at RF to provide a balanced output voltage + V1, - V2. Inverter driving circuit.-Fig. 4 shows a driving circuit suitable for use in block GOP for feeding drive pulses to terminals PQR for transistors 1, 2 of the main inverter IP. The driving circuit GOP comprises a master saturable-core self-oscillating square wave inverter comprising transistors 50, 51 and a slave inverter comprising transistors 65, 66. Winding 59 on the saturable transformer 49 provides synchronizing pulses for the slave inverter comprising transistors 65, 66 after a delay adjustable by impedances A, B coupled via transformer 62. The outputs of master and slave inverters are subtracked by secondary windings on transformers 49, 60 so as to provide a variable pulse-duration waveform similar to that shown in Fig. 2. This waveform is full-wave rectified by a diode bridge 28 ... 31 and a resulting D.C. subtracted from difference voltages so as to replace alternate half cycles by a pulse the duration of which is equal to the inter-pulse period. This action improves the turn off of transistors 1, 2 in the main inverter IP. Voltage regulation.-The converter output voltage at Z is fed to a long-tailed pair of transistors 84, 85 and compared with a Zener diode 83, the error voltage being used to change the impedance of transistor 75, the resulting change being reflected by transformer 62 to control the effective duration of driving pulses from GOP and hence control the converter output voltage. Protection.-The input current is monitored across resistor 3 and the resulting voltage coupled by transformer 9 to a voltage doubling rectifier 90 ... 93. The resulting voltage is amplified by transistor 94 and, if excessive (as determined by a Zener diode 96, changes the impedance of transistor 76 so as to reduce the effective output voltage. Over-voltage protection is achieved by diodes 97 and 101 which monitor the output voltage of the main inverter IP, after rectification at 37, 38. Starting.-Power for the driver GOP is normally obtained by rectification at 37, 38 of the main inverter IP voltage, but, for starting, a lower voltage derived from D.C. input via a stabilizer DA, is switched in by diodes 105, 106.