current and voltage. The 1524 also provides an accurate 5.1 volt DC reference which is used
for the under and over voltage lockout circuits. The PWM also contains an amplifier which
converts the error signals phase by 180° (at DC) so the signal into the PWM has the proper
phase. The PWM also provides an oscillator used to control the frequency of the pulse width
modulated signal.
4.5.8 PULSE WIDTH Modulator for the 2.5KW/5KW
U15 performs all the PWM functions. The industry standard UC3526 was chosen in this
application. Its primary function is to convert the differential analog signal on pins 1 and 2
to PWM signals on pin 16 and pin 13. The 5 Volts reference is used on the A100 board for
supervisory functions and for driving the input of the gate drive buffers. Pin 5 and pin 8 can
be pulled low for any fault condition by either Q5 in the supervisory circuit or by the current
limiting circuit.
4.5.9 Transistor Drive for the 600W/1KW
The outputs of U8 are “ORed” to provide a PWM signal at 50KHz. This is used as a clock
for the power MOSFET driver IC (U1) located on the A200 half bridge inverter board. The
totem pole outputs of the UC3706 drive T2. With the internal flip-flop active, the outputs of
U1 at pins 6 and 11 are alternating providing balance transformer drive and insuring that
only one transistor is turned on at a time.
4.5.10 Transistor Drive For the 2KW/2.5KW and 5KW
IXLD4429, an industry standard MOSFET driver, was chosen to drive the A200 Full Bridge
Inverter because of its high peak current capability and high speed. The output of the PWM
at pins 13 and 16 are alternating and are fed into the IXLD4429 MOSFET drivers. The
IXLD4429 drives the pulse transformer(s) providing the 180 degrees out of phase that is
required to keep only the diagonally opposite transistors conducting simultaneously.
83-473-000 Revision J
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Theory of Operation
