Three-Phase PWM Waveform Generator

The SA828 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.

The SA828 is fabricated in CMOS for low power consumption.

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 turn-on and turn-off times of families of power devices.

FEATURES

■ Fully Digital Operation

■ Interfaces with Most Microprocessors

■ Wide Power-Frequency Range

■ 12-Bit Speed Control Accuracy

■ Carrier Frequency Selectable up to 24kHz

■ Waveform Stored in Internal ROM

■ Double Edged Regular Sampling

■ Selectable Minimum Pulse Width and Underlap Time

■ DC Injection Braking