Instruction manual

105
5.12. AUXILIARY POWER SUPPLY
The auxiliary power supply uses the 300 VDC bus to generate all of the low voltage DC supplies
needed for amplifier operation. This switching supply delivers the following voltages:
1) ±15 VDC to the control board
2) +16 VDC to the lower gate drives on the front and rear amplifier boards
3) +16 VDC to the top rear amplifier
4) +16 VDC to the top front amplifier
5) +24 VDC to the DC fan.
All five DC supplies are isolated from one another. LED's on the power supply are lit when each
output is in regulation. If an overload condition causes an output voltage to drop more than 10%,
the corresponding LED will extinguish.
5.13. AMPLIFIER BOARDS
The power amplifier is a full bridge inverter made of two half bridges joined together. One half
bridge is the rear amplifier board, the other is the front amplifier board. Power MOSFET's are used
as the switching device in each quadrant of the bridge. Status of the gate drive to the MOSFET's is
indicated by LED's on the front and rear boards. Green indicates that the power FET should be on
and yellow off. When the unit is switching normally, both green and yellow LED's should appear
lit.
5.14. CONTROL BOARD
The main function of the control board is to generate the gate drive signals for the front and rear
amplifier boards. Other functions include overcurrent and overtemperature protection, and power
supply fault detection.
The SIG HI oscillator signal from the current limit board is low pass filtered and sent to the
reference input of the control board error amplifier. Differentially sensed output voltage closes the
loop to the error amp. The output of the error amp drives a 75 kHz pulse width modulator.
Modulator output is sent to two gate drive circuits which drive optical isolators to the full bridge
switching devices.