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Switching Regulator Start Up Circuit

IP.com Disclosure Number: IPCOM000086300D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Palmucci, CJ: AUTHOR

Abstract

This pulse width modulated regulator employs a "limit cycle" or variable-frequency, variable-pulse width (VFVP) regulator as a temporary source of bias during its start up. The VFVP regulator receives its initial power from a differentiating circuit responsive to application of line voltage, and then employs feedback from the main regulator filter before finally timing out and latching off after the main regulator has had time to ramp-up.

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Switching Regulator Start Up Circuit

This pulse width modulated regulator employs a "limit cycle" or variable- frequency, variable-pulse width (VFVP) regulator as a temporary source of bias during its start up. The VFVP regulator receives its initial power from a differentiating circuit responsive to application of line voltage, and then employs feedback from the main regulator filter before finally timing out and latching off after the main regulator has had time to ramp-up.

In the illustrated circuit, line voltage applied at A provides a pulse through capacitor C5 to capacitor C1, causing current to flow through capacitor C2 to resistor R1 so that transistor Q2 is turned on. This pulls current out of the base of transistor Q1, causing it to conduct. Transistor Q1 saturates and current flows through resistor R6 into the VFVP output load at point Z and charges up capacitor C3. As Z rises, voltage divider R2, R3 provides base voltage to transistor Q3.

When this becomes large enough, Q3 is turned on causing diode D4 to conduct base current away from transistor Q2, thus switching it to the off condition. Point Z begins to fall due to load current, until transistor Q3 is caused to switch off. This releases drive current for transistor Q2 and Q2 and Q1 are switched back on and the output voltage rises again.

The differentiated input voltage starts to decay after the first few milliseconds. However, by that time, main switch transistor Q4 has turned on, causing current...