GB1219437A - Improvements relating to power supply circuits - Google Patents

Abstract

1,219,437. Smoothing circuits for static rectifiers. BRITISH AIRCRAFT CORP. Ltd. 22 Aug., 1969 [23 Aug., 1968], No. 40496/68. Heading H2F. The D.C. output from a static A.C./D.C. converter (10), (Fig. 5, not shown), is smoothed by an arrangement in which each half sine wave is variably pulse width modulated, the pulse width being greatest where the voltage amplitude is least (Fig. 1, not shown), and if the resulting h.f. ripple is removed a constant output voltage waveform as shown, Fig. 2, is obtained. In addition, in order to fill in the troughs between the half waves storage capacitors are charged from the rectified current during an intermediate portion of each halfwave which includes the maximum amplitude thereof and the capacitors are discharged into the output of the smoothing circuit during the other parts of the half cycle. Figs. 3e, 3f, 3g illustrate the output power waveforms. Smoothing circuit operation.-An oscillator is started by a detector in response to the detection of a trough, and is synchronized to the converter A.C. input. It produces 32 pulses for each half cycle thereof which pulses are applied to a counter (30), Fig. 5 (not shown). The counter controls the pulse width modulation period and the capacitor storage charge and discharge periods. Thus at a count of 11 a trigger pulse fires a thyristor 13 (Fig. 7) which initiates charging of storage capacitors C 1 to C 10 . Each capacitor becomes charged to (2V-v) volts, the choke L 1 adding to the charge when the thyristor T 13 is turned off, (V being the input voltage to the smoothing circuit and v the remanent charge in C 1 to C 10 ). Charging continues until a count of 22. From a count of 28 in the same counting cycle until a count of 5 in the next counting cycle the ten capacitors are discharged sequentially via thyristors T 1 to T 10 , into the two halves alternately, of the primary of a transformer 16. When a discharge thyristor is fired a commutating capacitor C 11 causes the previously fired thyristor to turn OFF. From counts 6 to 27 the converter (10) output is pulse width modulated by chopping thyristors T 11 , T 12 which are fired alternately to give push-pull input to the transformer 16 primary. Firing of the chopping thyristors T 11 , T 12 is inhibited during the discharge of the capacitors. The transformer 16 feeds a plurality of output channels each of which include thyristors T 14 , T 15 which rectify and pulse width modulate the output to control the output voltage. Choke L 2 reduces the chopping frequency ripple (3.2 KHz). Diode D 11 is a free wheel diode. The pulse width modulation may be on the output side only of the transformer