Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
6-31
Section 6 Theory of Operation
Issue 1.1
SIMPLE CLASS 'D' OPERATION
If the switch is opened and closed with a 50%
duty cycle, a square wave at the switching
frequency will result at the filter input. If the
filter is designed to pass 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 is
designed to pass 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.
Figure 6-6 Simplified Principles of Class 'D' Operation
