Diodes Incorporated announced a family of pwm controllers designed to improve operating efficiency and eliminate no-load losses. The AP3125 current-mode devices have been optimized for use in offline ac-dc converters in portable products, consumer electronics and domestic appliances. The improvement in performance is a result of the devices’ three operating modes. In normal mode, switching frequency is either 65kHz or 100kHz. For a mid-range load, however, the controllers enter green mode, where frequency fold-back is used to back-off the frequency and raise average efficiency. Finally, in conditions of no-load or a very light load, the devices enter a burst mode to minimize standby power.
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To help minimize audible noise in the system, the SOT26-packaged AP3125 controllers have a minimum switching frequency setting of 20kHz, while a built-in frequency dithering function in normal and green modes ensures a reduction in EMI emissions. The controllers’ improved internal slope compensation helps to simplify feedback loop design and enables more stable peak current control over a wide range of input voltage and load conditions. In addition, the AP3125 family’s internal line compensation ensures output power limit is constant over the entire line voltage range.
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