carl said:
Can anyone explain how to me how burst fire control and phase angle control
work? or point me in the right direction, the text books i have don't really
cover these topics bar mentioning them briefly
thanks
Phase angle control varies the effective voltage by connecting the
load to the line only during some fraction of each half cycle,
starting at an adjustable point in each half cycle, and ending at the
next current zero crossing.
Burst control varies the effective average voltage (over a longer
time) by connecting the load to an integer number of complete half
cycles in a burst, and then disconnecting the load from the line for
some other integer number of full half cycles. Some systems use
integer full cycles, rather than full half cycles, to prevent any net
DC in the burst waveform. Burst mode has more low frequency ripple
than phase control, but makes less radio frequency and harmonic noise,
because all on switching is done very near the zero voltage points in
the line voltage wave and all switch off points are at zero current
points in the load current wave.
So phase control is better for ripple sensitive loads like stage
lighting and motors (where higher frequency ripple is worth the RFI
filtering needed), while burst mode is better for high power heating
elements that have a long thermal time constant.
