2-11.400 Hertz Switching Amplifier
a. The oscillator consists of a tank circuit, high gain
A22Q106 (0B-A21Q107, 0C-A21Q7) amplifies the
amplifier and a capacitor feedback. Transistor
Signal from the half wave retifier with A22Q107(OB-A21Q106,
OC-A21Q6) being used as a paraphase amplifier. Signals
A21Q4) (fig. FO-5) drives the tank circuit which is made up
are taken from both the collector and emitter in a
of A22L101, (OB-A21L1), A22C106, (OB-
paraphase amplifier because they switch exactly opposite
A21C105, OC-A21C5), and A22C104, (OB-A21C106,
to each other. The two opposing signals then drive
(OC-A21C6). To complete the oscillator circuit, A22C103
A22Q110 and Ql11 (0B-A2IQ105 and A21Q109, 0C-
provides the required feedback to the base of the oscillator
A21Q5 and A21Q9).
amplifier. The oscillator frequency (400 Hz 0.5 Hz) is
determined by the values of L101 with C106 and C104 in
2-12. Complementary Switch
parallel. To change the frequency of the oscillator, capacitor
Q110 and Ql11 work together as a complementary switch.
C 104 maybe changed. An increase of 0.01 microfarads will
If Q110 is turned "ON", Q1ll must be turned "OFF" and
produce a frequency decrease of approximately 3 hertz.
vice versa. This situation will continue through two stages
b. The oscillator has three functions. It is the reference
of amplification. In all cases if one half of the switch is
sine wave, the 400 hertz switch signal, and the inverter
"ON" the other half must be OFF.
regulating signal. As the reference sine wave, the oscillator
signal must have less than 2 percent harmonic distortion.
2-13. Inverter Switch Drive Transformer
After amplification, the output must match this signal. The
inverter can not meet the requirements if this signal has
a. Each pair of complimentary switches drives one
greater than 2 percent harmonic distortion. Regulation is
inverter switch transformer. A22Q110 and A22Q111 drive
determined by the peak to peak value of the signal. The AC
A2T3 for phase A. A2IQ105 and A21Q109 drive A2T2 for
error detector and the oscillator control circuits make the
phase B. A21Q5 and A21Q9 drive A2T4 for phase C.
peak voltage increase or decrease in response to the output
b. The interstage transformer has three centertapped
voltage through control of the error detector and oscillator
windings. The primary winding (pins 1 and 3) is driven by
the complementary switch. Pin 2 is tied to the + 16V dc.
Secondary N1 provides the base drive for the main power
2-9. Phase Locking
switch transistors. The power switch current will vary with,
a. The correct phase relationship and phase rotation for
the load but the complementary switch drive cannot
the three phase operation is established in the three
compensate for this. Since the base current must increase if
oscillator circuits. The positive zero voltage crossing of
the switched current increases, the emitter is tied to ground
phase B lags behind the positive zero voltage crossing of
through. secondary N2. An increase in switched current will
phase A by 120 or one third of a cycle. Similarly, phase C
assist in boosting the base current to the necessary level.
positive zero voltage crossing lags behind phase A positive
The inverter current sense is taken from the center top of
zero voltage crossing by 240 or two thirds of one cycle.
the base drive winding.
b. The oscillator coils each have
a secondary winding.
These are connected in delta with phase B and phase C
2-14. Inverter Switches
secondaries each having one end grounded. Phase A is the
predominant phase. The three secondaries form a single
Due to the very high currents which must be switched, six
winding. there is a 180 difference from ground through all
transistors are used for each phase. Phase A used A2Q20,
three windings and back to ground. At the one third points,
Q21 and Q22 and A2Q29, Q30 and Q31. Phase B used
the difference is only 60 from the ends. But if phase A is
A2Q17, Q18, and Q19and A2Q26, Q27, Q28. Phase C uses
the reference, add 60 and 180 (or invert the signal) ther
A2Q23, Q24 and Q25 and A2Q32 Q33 and Q34. Each
difference is 240, which is needed for phase C. For phase B
inverter switch drive transformer drives six transistors. For .
the phase signal precedes phase A by 60. The result is
each phase, three transistors will be "ON" and three
minus 60 plus 180 which equal 120. The inversion of
transistors will be "OFF". A low value resistor in each base
180 takes place on phase Bat the halfwave rectifier. The
drive circuit assists in stabilizing the base drive current.
inversion for phase C takes place by reversing the drive at
A2CR 10 through CR15 provide a clamp against negative
the interstage transformers.
voltage spikes. As the transistors are switched (three --
ON, three -OFF), the ends of the main transformer
2-10. Half and Full Wave Rectifiers
primary windings A3T1 are alternately grounded. Any
At the output of the oscillator, two rectifiers split the
current being applied to the center tap of the transformer
signal for different purposes. A22CR105 (fig. FO-3)
must switch back and forth to whichever end is grounded.
provides a positive going half wave rectified signal to the
400 hertz switching amplifier. A22CR 106 and
2-15. Pulser Circuit
A22CR107 (0B-A21CR104, A21CR106, 0C-A21CR4,
The pulser section controls the current being applied to the
A21CR6) provide a negative going full wave rectified
main transformer center tap. Paragraphs 2-16 through 2-20
signal to the pulser drive. The 400 hertz switching is
describe the pulser operation.
discussed first followed by the pulser drive.