Patent GB-1302298-A (GB)
IPC: H02M3/337
Filed: 1970-03-26
Abstract: 1302298 Converting SODILEC SA 26 March 1970 [27 March 1969] 14948/70 Heading H2F [Also in Division G3] A D.C.-D.C. converter with stabilized output voltage comprises push-pull chopper transistors 2, 3 controlling the primary winding 4 of a transformer whose secondary winding 5 is passed to a rectifier and filter 6, NAND gates 12, 13 which control the transistors and are controlled by a master oscillator consisting of a fixed high frequency multivibrator 9 and by a flip-flop 14, a feedback control circuit formed by a differential amplifier 24 which compares the output voltage 7 with a reference voltage 25 and thereby controls the rate of rise of a sawtooth waveform produced by a current generator 20 and capacitor 21, the sawtooth and another reference voltage 19 being fed to a further differential amplifier comparator 15, and a transformer 16 which provides D.C. isolation between member 6 and members 2, 3, 12, 13, the control circuit supplying the flip-flop 14 with a recurrent pulse whose time of occurrence is an inverse function of the output of the amplifier 24, such that the mark/ space ratio of the transistors 2, 3 is varied to maintain the output voltage at the desired value. A synchronization control circuit 23 defines the periods during which the control pulses occur and is coupled to the multivibrator 9 through a transformer 22 also providing D.C. isolation between the output and input of the converter. The following protection circuits are provided:- (1) Circuit 27, 28, 29 short circuits the reference voltage 25 (which may be a Zener diode) whenever the current through resistor 27 exceeds a predetermined value, the latter being set by a reference voltage in the element 28 which includes a transistor circuit switchable to connect the voltage 25 to earth through diode 29. (2) Differential amplifier comparator 30 which, whenever the output voltage 7 exceeds a predetermined value set by a reference voltage 31, triggers a thyratron 32 which short circuits the output voltage 7. Also, when the thyratron is triggered a transistor in circuit 33 becomes conductive to energize a relay 34, which triggers another thyratron 35 to inhibit the gates 12, 13 and so turn off the transistors 2, 3. Alarm lamp 37 is also energized. The relay 36 provides further D.C. isolation between the input and output sides of the converter. (3) Differential amplifier comparator 38 which, whenever the output voltage 7 falls below a predetermined value set by a reference voltage 39, energizes an alarm lamp 40. A description is given of the current generator 20, Fig. 3 (not shown), and the operation of the control circuit, Fig. 2 (not shown). A starting circuit 45 is provided, after which the gates 12, 13 are energized by a low voltage obtained from transformer 4, 5 and rectified. In another embodiment, Fig. 4 (not shown), the error signal from the first differential amplifier comparator (55) is supplied to a lightemitting diode (66a) which controls a phototransistor (66b) in a transistor-diode circuit (69), whose output is passed to the NAND gates (52, 53). These gates are also controlled by the flip-flop (54) which, with the circuit (69), is controlled by the master oscillator (64) consisting of a uni-junction transistor and R.C. circuit, Fig. 5 (not shown), operation of the control circuit under normal and overcurrent conditions is described.