Browse Prior Art Database

120/220 VAC Auto-Ranging, Battery-Supported, High Voltage Supply

IP.com Disclosure Number: IPCOM000040555D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Ashley, DJ: AUTHOR

Abstract

Many uninterruptible power supplies are commercially available but experience problems such as continuously drawing current from batteries, limited to operating on either 120 VAC or 220 VAC, or having a voltage glitch on the output when transitioning from the AC line to batteries, etc. The use of a high frequency, square-wave push-pull inverter virtually eliminates these problems, while reducing overall size and weight. A circuit configuration, described herein, allows for the external application of various types of ni-cad batteries to specify how long battery operation will last. This circuit also automatically disconnects the external batteries prior to completely discharging them, provides AC line isolation to comply with safety standards, and a trickle charger to recharge the ni-cad cells.

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120/220 VAC Auto-Ranging, Battery-Supported, High Voltage Supply

Many uninterruptible power supplies are commercially available but experience problems such as continuously drawing current from batteries, limited to operating on either 120 VAC or 220 VAC, or having a voltage glitch on the output when transitioning from the AC line to batteries, etc. The use of a high frequency, square-wave push-pull inverter virtually eliminates these problems, while reducing overall size and weight. A circuit configuration, described herein, allows for the external application of various types of ni-cad batteries to specify how long battery operation will last. This circuit also automatically disconnects the external batteries prior to completely discharging them, provides AC line isolation to comply with safety standards, and a trickle charger to recharge the ni- cad cells. The battery-supported high voltage output will supply any off-the-shelf DC-DC converter plugged into it. This power supply features a constant high DC voltage output derived from the rectified AC Line or the secondary of a battery- operated square-wave inverter. The AC line input may be 120 VAC 60 Hz or 220 VAC 50/60 Hz. This is made possible by an AC auto-ranging circuit. The auto- ranging feature is accomplished by sensing a DC control voltage produced by a control transformer T1 and voltage doubler D4, D5, C6, C7. If the AC line voltage is 120 VAC, only half as much DC control voltage is available as when in 220 VAC operation. Comparator C1 will drive relay coil K1 via transistor Q2 when the DC control voltage available is equivalent to the 220 VAC input. The K1 relay contacts are in series with the center tap of the high DCV output capacitors C4, C5 and, therefore, double the rectified AC input voltage when operating from a 120 VAC line. If operating from 220 VAC, the auto-ranging comparator C1 will pick K1, opening the center tap to the high DCV output capacitors C4, C5 so as not to double the rectified AC input voltage. This maintains a nominal rectified AC line voltage of 320 VDC out during nominal AC Line operation. If the AC line voltage begins to drop, comparator C2 switches relay K2 on. The +24 VDC from the battery will be applied to a square- wave inverter, consisting of a 555 astable oscillator, 74107 flip-flop, gate drive transistors Q3, Q4 and power FETs F1, F2. The +24 VDC battery input will be converted into 240 VDC via power transformer T2 and bridge rectifier B2. Because bridge rectifier B2 is dotted across the high DCV output capacitors C4, C5, a smooth transition from AC line to batteries will be realized. During normal AC line operation, comparator C2 holds relay contacts K2 open and the square- wave inverter is non-operational because the +24 VDC battery can not supply the 5...