Different power-supply specifications drive the need for different power-supply topologies. These different power-supply topologies require various types of PWM modes. Each PWM mode play an important role in wide variety of SMPS designs including standard, push-pull, complementary, multi-phase, current-reset, variable-phase and current-limit PWM modes.
The most common PWM mode is the standard edge-aligned PWM. In this mode flow of power controls by the ratio of the on time verses the off time. Only one of the PWM outputs per output pair is used in these Asynchronous Buck, Boost and Flyback converter circuits.
Push-pull converters are mostly used in AC/DC power supplies and DC/DC converters. The term "multiphase PWM" means multiple PWM outputs that are not edge-aligned. Multiphase converter circuits are mostly used in DC/DC converters that must supply high current in applications where the load may change very rapidly.
Our Synchronous Buck Converter uses a complementary PWM mode, where the complementary output controls a "synchronous switching" rectifier that is implemented with a MOSFET, instead of the typical rectifier. The complementary PWM mode can also be used in other circuits that use synchronous rectification to improve system efficiency.
Phase-shifted PWM mode is widely used in personal computer power supplies so that it is becoming more common mode. SMPS family supports all of the known PWM modes currently in wide use by the power-supply industry.
A pulse width modulation (PWM) generator featuring very high speed and high resolution capability and the ability to generate standard complementary PWM, push-pull PWM, variable offset PWM, multiphase PWM, current limit PWM, current reset PWM, and independent time base PWM while further providing automatic triggering for an analog-to-digital conversion (ADC) module that is precisely timed relative to the PWM signals. Applications include control of a switching power supply that requires very high speed operation to obtain high resolution at high switching frequencies, and the ability to vary the phase relationships among the PWM output signals driving the power supply power components. A single PWM duty cycle register may be used for updating all PWM generators at once to reduce the workload of a digital processor as compared to updating multiple duty cycle registers.
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