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Non-Dissipative Clamp for Large Duty Cycle Switching Power Supply

IP.com Disclosure Number: IPCOM000046762D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Weekly, RD: AUTHOR

Abstract

This is a secondary clamping circuit for application in a single switch variable duty cycle switching regulator power supply. This circuit allows switching transistors to be used to their specified performance levels and allows for substantially greater than 50% duty cycle operation. In addition to the secondary clamping circuit a leakage clamp is also employed to handle the primary energy not coupled into the secondary clamp. In the figure, when transistor Q1 is on, capacitor C1 is charged through diode D1 to a voltage proportional to the bulk DC voltage VB. When Q1 is turned off, the voltage across transformer T1 reverses in polarity and increases in magnitude until diode D2 is turned on. This clamps the transformer voltage at the output voltage VO2 minus the voltage across C1.

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Non-Dissipative Clamp for Large Duty Cycle Switching Power Supply

This is a secondary clamping circuit for application in a single switch variable duty cycle switching regulator power supply. This circuit allows switching transistors to be used to their specified performance levels and allows for substantially greater than 50% duty cycle operation. In addition to the secondary clamping circuit a leakage clamp is also employed to handle the primary energy not coupled into the secondary clamp. In the figure, when transistor Q1 is on, capacitor C1 is charged through diode D1 to a voltage proportional to the bulk DC voltage VB. When Q1 is turned off, the voltage across transformer T1 reverses in polarity and increases in magnitude until diode D2 is turned on. This clamps the transformer voltage at the output voltage VO2 minus the voltage across C1. The following derivation illustrates that the collector-to-emitter voltage at Q1 is substantially limited to a voltage which is constant and independent of the duty cycle:

(Image Omitted)

Although the clamp voltage is independent of bulk voltage VB or duty cycle, a relationship between the maximum allowed duty cycle, the clamp voltage, and the bulk voltage may be made which is the point at which core walk-up begins. To prevent core walk-up the volt-time during the on time of Q1 must be less than or equal to the possible volt-time during the off time of Q1, or:

(Image Omitted)

During steady state for a forward converter, bu...