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PWM controllers boost operating efficiency, minimise noise

Posted: 09 Feb 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Diodes? PWM controller? AC-DC converter? consumer electronics?

Diodes Inc. has introduced a line of PWM controllers that promises to enhance operating efficiency and eliminate no-load losses. According to the company, the AP3125 current-mode devices are optimised for 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 cut standby power.

To help reduce 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 allows more stable peak current control over a 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.

To help increase system reliability, the controllers also integrate a more complete range of protection functions than competing devices, stated Diodes. Internal over-temperature protection and fast over-current protection are included, along with over-voltage and overload protection. The AP3125B and AP3125HB variants also integrate brownout and line over-voltage protection, easily configured using a few divider resistors.

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