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motor controller tracks position by monitoring the channel A and B lines from the position sensor to determine
the sum of the movement away from this known index position. SERVO_INDEX_BIT = high when pointed at
plano #1.
4.4.5 HVPS & Control Circuits
The HVPS and Control Circuits oversee the control and turn-on of the flashlamps, monitor the voltage on the
capacitor bank, and monitor several status signals from the high voltage power supply.
Refer to the HVPS & Interface Circuits Simplified Diagram (Figure 4.4) and to the related schematics in
Section 8. The capacitor bank is charged by a Coherent manufactured high voltage power supply (HVPS).
The control circuit on the Controller PCB sends the HVPS a LAMP DR. I, II, III or IV signal, LAMP_MOD,
LAMP_VOLTS signal and the CROWBAR signal. The HVPS sends a CROWBAR_OK and F-FEEDBACK
signals to the Controller PCB.
To turn on a particular flash lamp, the Safety Control Logic EPLD U40 on the Controller PCB routes a fire pulse
(L1_LAMP_DRIVE, L2_LAMP_DRIVE, L3_LAMP_DRIVE, or L4_LAMP_DRIVE) through the Fiber Optic
Driver (U19) and then to one of the four transmitters on the Controller PCB. When the fire pulse is asserted,
the selected transmitter will turn on, emitting a 660nm light through the fiber optic to the HVPS. Enabling the
Insulated Gated Bipolar Transistor (IGBT) driver PCB and turning on the IGBT. Creating a complete path for
current discharge through the selected lamp.
CHARGING PROCESS - The microprocessor first calculates the lamp energy parameters required to provide
the selected pulse energy at the selected pulse rate. The selected energy and pulse rate index a lamp energy
current value in the stored calibration data. The data is established during automatic laser calibration and
updated by light feedback information from any previous pulses at the selected operating point.
The first pulse of a treatment delivery (i.e., the first pulse after the footswitch is depressed) includes a
correction factor to compensate for differences in cavity output that occur before the thermal lens has formed.
Subsequent pulses do not require this correction factor.
The microprocessor writes the digital value for the required voltage to the Lamp Volts Frequency Generator
U45. U45 outputs a frequency range of 0 to 100kHz for a main capacitor charging voltage of 400 volts to 800
volts. The voltage/frequency signal is sent an amplifier U43 and out through transmitter XMIT6 to become
LVOLTS, of the Controller PCB to the HVPS module. In the VersaPulse Select III, the lamp voltage is fixed at
800 VDC.
The LVOLTS drive signal from the Controller PCB enters into the Mother board on the HVPS. The signal exits
from the Mother board and into the Power Supply Controller PCB as VOLTCONTROL. The signal is fed into a
Frequency-to-Voltage Receiver/Converter U38 for the requested B+ voltage. This circuit converts a frequency
range of 0 to 100kHz to a resistor ladder. The frequency is converted to a voltage by U38 on the Power Supply
Controller at a constant rate of 10kHz per volt. An output voltage from U38-1 is filtered by two RC filters and
buffered by U39-7. The output from U39-7 becomes the input to the free running A/D converter U28. The
digital output becomes input to the digital latch U27, which sets the various analog switches corresponding to
the requested voltage, telling the boost regulator what voltage level to change the capacitor bank up to.
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