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Variable on Period Flyback Drive

IP.com Disclosure Number: IPCOM000084643D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Hoffman, HS: AUTHOR

Abstract

This transistor switching circuit employs flyback on-drive, regenerative maintenance, direct off-drive and off-clamping in a variable on-period circuit suitable for a transistor switching regulator.

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Variable on Period Flyback Drive

This transistor switching circuit employs flyback on-drive, regenerative maintenance, direct off-drive and off-clamping in a variable on-period circuit suitable for a transistor switching regulator.

In Fig. 1 a clock controlled input pulse applied at terminal 8 turns transistor driver 10 on for the duration of the pulse, a fixed period. As shown in Fig. 2, the driver current 12 through primary 14 of transformer T will build-up to the current limit 16 fixed by emitter resistor 18, and remain there until the end of the fixed period. The flyback current 20, generated in coil 22 as the result of the turn off of transistor 10, will turn on main transistor 24. Regenerative on-drive from coil 26 to coil 22 keeps transistor 24 on, even though the fly-back current component 20 of its drive proceeds to fall to zero and goes to a negative current component 28.

At some point during transistor 24 on-time and before T reaches saturation, transistor 10 is again turned on by a pulse applied at terminal 8 by control CTRL responsive to the regulator feedback, not shown. Driver 10 current 30 loads T so as to pick up the regenerative drive current and allow off-drive current 32 to flow from transistor 24 through coil 22 until storage in transistor 24 ends.

When the currents in coils 22 and 26 go to zero, transistor 10 collector falls but is clamped by diode 36, resetting T. The diode drop through diode 36 signals CTRL via line 38 to turn off transist...