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Browse Prior Art Database

Reduction of Ripple Voltage when Leaving Burst Mode

IP.com Disclosure Number: IPCOM000170210D
Original Publication Date: 2008-Jun-03
Included in the Prior Art Database: 2008-Jun-03
Document File: 3 page(s) / 375K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Electronic devices such as the Coolset F3 controller can be used as AC/DC converters with low standby power. This device provides an Active Burst Mode function to enable the system to achieve a low standby power when the load condition is low. Active Burst Mode means that the device is always in active state and can therefore immediately response to any change in the FB (Feedback) signal VFB. The controller also provides a blanking time before entering the Burst Mode. This ensures that the system will not enter Active Burst Mode unintentionally. The blanking time is generated by charging a soft-start capacitor from 4.4 V to a maximum of 5.4 V. The gate drive is still activated during this time period even at overload condition when the feedback voltage rises up to above 4.8 V.

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Reduction of Ripple Voltage when Leaving Burst Mode

Idea: Gong Xiaowu, Ph.D., SG-Singapore; He Yi, SG-Singapore

Electronic devices such as the Coolset F3 controller can be used as AC/DC converters with low standby power. This device provides an Active Burst Mode function to enable the system to achieve a low standby power when the load condition is low. Active Burst Mode means that the device is always in active state and can therefore immediately response to any change in the FB (Feedback) signal
VFB. The controller also provides a blanking time before entering the Burst Mode. This ensures that the system will not enter Active Burst Mode unintentionally. The blanking time is generated by charging a soft-start capacitor from 4.4 V to a maximum of 5.4 V. The gate drive is still activated during this time period even at overload condition when the feedback voltage rises up to above 4.8 V.

A problem occurs when leaving the Burst Mode. During Burst Mode operation, VFB swings from 3.4 V to 4.0 V. When VFB > 4.0 V, the controller will be switched on; when VFB < 3.4V, the chip will be switched off. If during Burst Mode operation, the load condition increases, the output voltage will drop accordingly and make VFB increase. This increased VFB will first pass the threshold voltage 4.0 V and let the controller work in Burst Mode on-state. Now, the peak current sense limitation voltage is only
0.25 V which does not provide high power to the secondary side. This can lead to not fulfilling power requirements and cause the output voltage to drop further and VFB to ramp up. When VFB reaches 4.8 V, the chip will leave the Burst Mode operation, the current limitation will become 1.0 V and more power is delivered to the secondary side. The ramping up of V...