Circuit for continuous variation of AC or DC current in load operated from AC or DC supply or combination supply e.g for heating systems

摘要

The circuit connects the supply network to the load (10) and contains a low pass filter (12) which achieves a continuous input current, and a coil (14) in series with or part of the load. A first a.c. switch (16) is in parallel with the load and coil, and a second a.c. switch (32) is driven at a frequency higher than the supply frequency and connected in series with the load. A controller (34) detects the a.c. or d.c. load current directly or indirectly, has an input for a desired a.c. or d.c. load current and drives the second switch with a suitable switching frequency and duty cycle to achieve the desired load current.