Nautel XR12, Troubleshooting Manual, Page: 98 / 283

XR12 Troubleshooting Manual Detailed Circuit Descriptions
Page 2-30 Issue 3.0 2009-07-28
Figure 2.2: Simplified Principles of Class ‘D’ Operation
Simple Class 'D' Operation
If the switch is opened and closed with a
50% duty cycle, a square wave at the
switching frequency results at the filter
input. If the filter passes the switching
frequency, but attenuate its harmonics, a
sine wave is applied to the load.
Push Pull Class 'D' Operation
If S1 and S2 are opened and closed with a
50% duty cycle, a square wave of current,
at the switching frequency, is passed
through the primary of the transformer
and transformed to its secondary. If the
filter passes the switching frequency, but
attenuate its harmonics, a sine wave is
applied to the load.
Power MOSFET Class 'D' Operation
Power MOSFETs can be used to replace
the switches as depicted in the simple class
'D' operation and push-pull class 'D'
operation examples. Note that the switch
contacts are replaced by the phase-
oriented secondaries of an RF drive
transformer. Q1 corresponds to S1-A, Q2
to S1-B, Q3 to S2-B and Q4 to S2-A, as
depicted in the push-pull class 'D'
operation example. Q1 and Q4 turn on/
off together and Q2 and Q3 turn on/off
together.