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Auxiliary Regulator for Switching Power Supply

IP.com Disclosure Number: IPCOM000062552D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Kinnard, JR: AUTHOR

Abstract

An arrangement to improve efficiency of power supplies requiring auxiliary regulators is described. The switching frequency of switch mode power supplies has been steadily increasing and components are now available which allow operation at several hundred kilohertz. At these higher frequencies, very little power transformer inductance is required and a 5-volt output may be achieved with a single turn of wire. If a 12-volt output is needed (Image Omitted) in addition to the 5 volts, a 'hit' problem results. Two turns of wire will produce 10 volts, and three turns will produce 15 volts. Special winding techniques can produce partial turns, but they usually suffer from poor voltage regulation.

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Auxiliary Regulator for Switching Power Supply

An arrangement to improve efficiency of power supplies requiring auxiliary regulators is described. The switching frequency of switch mode power supplies has been steadily increasing and components are now available which allow operation at several hundred kilohertz. At these higher frequencies, very little power transformer inductance is required and a 5-volt output may be achieved with a single turn of wire. If a 12-volt output is needed

(Image Omitted)

in addition to the 5 volts, a 'hit' problem results. Two turns of wire will produce 10 volts, and three turns will produce 15 volts. Special winding techniques can produce partial turns, but they usually suffer from poor voltage regulation.

The simplest and usually least expensive solution to the hit problem is to produce 15 volts with a three-turn winding and use a linear regulator to reduce the 15 volts to 12 volts. The linear regulator will dissipate 25% as much power as the 12-volt load, but this is often acceptable at lower power levels. At power levels where the linear regulator dissipation becomes excessive, or when power supply efficiency is critical, an auxiliary switching regulator can be used to reduce the 15 volts to 12 volts with much greater efficiency than the linear regulator. Fig. 1 indicates how the auxiliary switch is most often applied and the resulting waveforms. The main disadvantage of the standard configuration in Fig. 1 is the difficulty of driving the control input of the auxiliary switching device. The reference terminal of the auxiliary switch (the source for the FET in Fig. 1) is at the most positive voltage on the secondary side of the power supply, and this creates difficulty in turnin...