Browse Prior Art Database

Dissipation Reduction in Transistor Switching Regulator

IP.com Disclosure Number: IPCOM000086694D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Johari, GC: AUTHOR

Abstract

Series switching regulators feeding an LC-freewheeling diode filter have the problem that during the turn-off transition of the switch, the inductor is in heavy conduction and the diode is not yet ready to conduct that current, and during the turn-on transition the diode has not yet recovered whereby the switch sees a virtual short circuit. Various networks have been proposed to alleviate this problem, generally treating the two transitions separately and producing a compromise result.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 3

Dissipation Reduction in Transistor Switching Regulator

Series switching regulators feeding an LC-freewheeling diode filter have the problem that during the turn-off transition of the switch, the inductor is in heavy conduction and the diode is not yet ready to conduct that current, and during the turn-on transition the diode has not yet recovered whereby the switch sees a virtual short circuit. Various networks have been proposed to alleviate this problem, generally treating the two transitions separately and producing a compromise result.

The circuit of Fig. 1 combines turn-on and turn-off suppression features in an advantageous manner, and operates as follows:

Turn-Off Suppression (Figs. 1 and 2): When switch SW is on, point A goes to full input voltage E and capacitor C1 charges through R1. The value of resistor R1 is selected such that the time constant R1C1 = 1/3 (minimum on time). Larger values of C1 decrease turn-off dissipation in SW, but increase charging current at the time of the turn-on transition. These two conflicting requirements on the value of C1 can be met only by compromise and proper weighting of thermal stresses in SW during the turn-on and turn-off transitions.

At the time of turn-off, point A is supported by the capacitor C1 and supplies current to the choke L1. Thus the current in SW is allowed to reduce without building a large voltage drop across the switch. Since L1 << L(F), the current in L1 decreases along with the discharge of C1 and thus the rate of change of voltage at A decreases, which is effectively the same as increasing the value of C1. The decreased current in L1 (or C1) comes from C2, which in...