switch mode power supply What does frequency foldback do in a switching regulator


Posted on Feb 5, 2014

When VOUT is very low during start-up or a short-circuit fault on the output, the switching regulator must operate at low duty cycles to maintain the power switch current within the current limit range, since the inductor current decay rate is very low during switch off time. The minimum on-time limitation may prevent the switcher from attaining a sufficiently


switch mode power supply What does frequency foldback do in a switching regulator
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low duty cycle at the programmed switching frequency. So, the switch current will keep increasing through each switch cycle, exceeding the programmed current limit. To prevent the switch peak currents from exceeding the programmed value, the LT3759 contains a frequency foldback function to reduce the switching frequency when the FBX voltage is low (see the Normalized Switching Frequency vs FBX graph in the Typical Performance Characteristics section). Some frequency foldback waveforms are shown in the Typical Applications section. The frequency foldback function prevents IL from exceeding the programmed limits because of the minimum on-time. This seems different from foldback short circuit protection. But how does frequency foldback work What would be a good analogy to its process What would the plot look like without frequency foldback




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