GB1529712A - Dc/dc converter power supply circuits - Google Patents

Abstract

1529712 DC-DC converters SIEMENS AG 4 Sept 1975 [20 Sept 1974] 36382/75 Heading H2F A D.C.-D.C. converter comprises a switching transistor T1 connected through the primary winding L1 of a transformer across the output of a rectifier bridge B, a secondary winding L2 of the transformer and members D2, C2 providing a D.C. output voltage U A determined by a control circuit R for transistor T1, the circuit R being supplied with an operating voltage from an auxiliary winding L3 of the transformer through diode D5 and with a starting voltage (when T1 is initially non-conductive) from a starting circuit E whereby, when a switch S is closed to energize the bridge B, a capacitor C11 is charged through resistors R11, R13 until a trigger diode D11 breaks down and fires a thyristor Ty11, which thereupon transfers the charge on C11 through a surge limiting resistor R14 to a capacitor C12 connected to the input of circuit R. Capacitor C12 subsequently controls a transistor T12 which is turned on by the voltage produced across capacitor C12 by members L3, D5 so that capacitor C11 cannot charge during this condition. A circuit comprising members T11, R12, R13, D12 responds to the appearance of a surge voltage at the output of bridge B and turns on transistor T12 to prevent charging of capacitor C11 during the surge condition. Circuit R comprises an operational amplifier VI receiving, from members L3, D3, C4, R1, a signal representative of the output voltage U A and, from members R2, D4, a desired output voltage signal, and a comparator V2 and transistor T2 to provide feedback and control the switching of transistor T1. The starting circuit may be modified, Fig. 2 (not shown), by replacing the resistor R14 by a choke (L51) and using an extra transistor (T52) to short circuit the capacitor (C51) during a surge condition, the latter transistor also controlling the amplifier V1 to switch off the transistor T1, if the output voltage of bridge B exceeds a value corresponding to that set by Zener diode D4. A Zener diode (D55) in the other transistor (T53) circuit shunting capacitor (C51) prevents its complete discharge in order to enable this capacitor to supply a transistor (T51) responsive to the output of bridge B. The thyristor Ty11 may be replaced by a unijunction transistor. Other modifications are the use of the converter output voltage to supply the circuit R after starting and the omission of capacitor C12, in which case the thyristor Ty11 remains on after starting so that capacitor C11 is charged by the supply L3, D5 or the converter output voltage.