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Driver Circuit For Switching Regulator

IP.com Disclosure Number: IPCOM000048941D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Radcliffe, JK: AUTHOR

Abstract

Base drive circuit 10 (Fig. 1) maintains a constant ratio between the rising base current Ib (Fig. 2) and collector current Ic of a switching regulator transistor Q1.

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Driver Circuit For Switching Regulator

Base drive circuit 10 (Fig. 1) maintains a constant ratio between the rising base current Ib (Fig. 2) and collector current Ic of a switching regulator transistor Q1.

Transistor Q1 is, by way of example, part of a power stage 11 configured as a self-oscillating triangular-wave flyback converter. Q1 is serially connected to the primary winding N1 of flyback transformer T1, whose output winding N3 provides the regulated output voltage Vo. Feedback winding N2 of transformer T1 drives the base of Q1 through circuit 10 which is connected across Q1's base and emitter electrodes B and E, respectively, and which periodically turns Q1 on and off.

At time t1, Q1 turns on and its collector voltage V1 goes to zero, i.e., ground. The collector current Ic, which is initially at zero, rises as a linear ramp with an approximate slope Vc/Lc, where Lc is the inductance of transformer T1. When transistor Q2 turns on, it connects the base of Q1 to ground thereby turning off transistor Q1 at time t2. During the turn-off period, the collector of Q1 goes positive and the energy stored in transformer T1 is delivered to the output winding N3. The voltage across transformer T1 decays. inducing a voltage in N2 which turns Q1 on after the stored energy has been delivered and thus begins the turn-on period of the next cycle.

To compensate for inefficiencies due to the wide variation expected for current Ic for the various applications for which Q1 is designed, an inductor L is incorporated in drive circuit 10. It can be shown that this causes the base current Ib to vary in the same fashion as the collector current.

More particularly, during the on period of Q1, the bulk voltage Vc is coupled to N2 and causes current IL in inductor L to rise with a s...