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Voltage Regulator Having Coupled Filter for Fast Load Transient Response

IP.com Disclosure Number: IPCOM000060405D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

McCoy, WB: AUTHOR [+2]

Abstract

In a conventional forward-averaging output of a switching supply, the filtering is done at the voltage and current levels of the output, as shown by the portion of the diagram not enclosed in the dotted line A. For low voltage, high current outputs, this filtering becomes unwieldy because (1) capacitive energy storage at low voltage requires large capacitor values and (2) use of large inductances at high currents results in physically large structures (because of the large cross- section needed for both the wire and the core), and slows the supply's speed of response to changes in load current. By adding an ancillary winding to the transformer T and driving the circuit A shown enclosed in the dotted line, the need for output filtering at the supply voltage and current can be reduced.

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Voltage Regulator Having Coupled Filter for Fast Load Transient Response

In a conventional forward-averaging output of a switching supply, the filtering is done at the voltage and current levels of the output, as shown by the portion of the diagram not enclosed in the dotted line A. For low voltage, high current outputs, this filtering becomes unwieldy because (1) capacitive energy storage at low voltage requires large capacitor values and (2) use of large inductances at high currents results in physically large structures (because of the large cross- section needed for both the wire and the core), and slows the supply's speed of response to changes in load current. By adding an ancillary winding to the transformer T and driving the circuit A shown enclosed in the dotted line, the need for output filtering at the supply voltage and current can be reduced. The coupling M and turns ratio of the inductors L and LA can be arranged so that substantially reduced (ideally zero) ripple occurs in the output load RL . For this operating condition, M/LA = Vout/VA . The ancillary circuit A must dissipate minimum power in order to perform this function without allowing the current to be reduced to zero in either inductor. This power is dissipated in RA and is given by: PA = (1/2 VoutWi)/k2 where: Wi = ripple current which would occur in L without inductive coupling, and k2 = M2/LAL = (coupling coefficient)2 Because of the inductive coupling, circuit A can be chosen for effici...