Analysis of the noise and efficiency characteristics in a quasi-resonant converter
A quasi-resonant converter using flyback topology can realize soft switching with relatively simple circuit. However, a switching device with high withstand voltage is necessary to achieve complete zero voltage switching when the input voltage is high and it causes decrease of efficiency because a switching device with high withstand voltage has relatively high on voltage. Therefore, we analyzed efficiency and noise of a quasi-resonant converter with a low breakdown voltage and low on voltage switching device under the condition of non-zero voltage switching. As a result of the analysis, it is found that high efficiency and low noise are achieved with non-zero voltage switching.
An adaptive blanking time control scheme for audible noise free quasi resonant Flyback converter
The quasi resonant (QR) control scheme is widely adopted in Flyback converter to maximize its efficiency by reducing the switching loss. However, the maximum frequency limitation adopted in QR control may cause the audible noise due to the frequency hopping phenomena at certain load and input condition, which is related to the intrinsic output characteristic of the control scheme. This paper presents a simple solution to eliminate the frequency hopping in the QR Flyback using an adaptive blanking time circuit. The proposed method changes the blanking time automatically to keep the output characteristic smoothly which eliminate the audible noise in the transformer. The detailed operation principle and design considerations are presented. The experimental results from a 16V/4A prototype are provided to validate the effectiveness of the proposed solution.
Analysis of surge and noise generation in a forward dc-to-dc converter
Switching surge and noise voltages are analyzed under the common-mode condition in a forward dc-to-dc converter, which is the most popular converter. The analysis is performed by partitioning the switching time into several states and introducing the high-frequency equivalent circuit corresponding to each state. The equivalent circuits include not only inductive or capacitive parameters but also the parameters related to the transistor's switching speed and the diode's recovery characteristics. As a result the effects of these various parameters on the surge and noise generation are made clear quantitatively. Particularly an important feature of the relationship between the transistor's switching speed and the surge and noise voltages is obtained.