MA818

THIS DOCUMENT IS FOR MAINTENANCE PURPOSES ONLY AND IS NOT RECOMMENDED FOR NEW DESIGNS ADVANCE INFORMATION 3797-2·2 MA818 THREE-PHASE PULSE WIDTH MODULATION WAVEFORM GENERATOR The MA818 PWM generator has been designed to provide waveforms for the control of variable speed AC machines, uninterruptible power supplies and other forms of power electronic devices which require pulse width modulation as a means of efficient power control. The six TTL level PWM outputs (Fig. 2) control the six switches in a three-phase inverter bridge. This is usually via an external isolation and amplification stage. Rotational frequency is defined to 12 bits for high accuracy and a zero setting is included in order to implement DC injection braking with no software overhead. Any power waveform can be implemented as this is user-defined in an external PROM/ EPROM. For users requiring an on-chip pre-programmed waveform, the functionally identical MA828 is recommended. Information contained within the pulse width modulated sequences controls the shape, power frequency, amplitude, and rotational direction (as defined by the red-yellow-blue phase sequence) of the output waveform. Parameters such as the carrier frequency, minimum pulse width, and pulse delay time may be defined during the initialisation of the device. The pulse delay time (underlap) controls the delay between turning on and off the two power switches in each output phase of the inverter bridge, in order to accommodate variations in the...