technical reference
35
Synrad
Series 48Series 48
Series 48Series 48
Series 48 operator’s manual
Technical overview
Fault shutdown conditions
The power input circuit consists of a panel-mounted fuse for overcurrent protection, a dual Schottky
shunt rectifier for reverse-voltage protection, a panel-mounted keyswitch, and a normally open MOSFET
safety switch. Application of reverse-voltage will normally require fuse replacement.
The output of the Keyswitch is connected to the control board through the DB9 Connector user port.
Note that the supplied DB9 jumper plug can be removed to allow the user to insert a remotely located
relay or switch in series with the Keyswitch. If the Keyswitch is left on or is electrically bypassed, the user
can turn the laser on and off, and reset fault shutdowns from a remote location.
The temperature warning message output (pin 5 of the DB9 connector) goes low when the laser tube
temperature reaches 54 °C ±2 °C and remains low until tube temperature falls 2 °C below the trigger
temperature. The warning message output does not shut down the laser. Over temperature fault shut-
down occurs when laser tube temperature reaches 60 °C ±2 °C.
Control board operation begins when the supply voltage rises above +18 VDC and remains below +36
VDC. After start-up, the control board will shut the laser down if supply voltage falls below +15 VDC or
rises above +36 VDC.
If an electronics failure causes the control board to output PWM power to the RF Drivers in excess of
20% of the commanded PWM input, a fault shutdown will occur.
To reset after any fault shutdown, correct the problem(s) then cycle the Keyswitch (or Remote Keyswitch
if one is present) or remove power to the laser for 30 seconds. During any fault shutdown, the fault
shutdown output (pin 1 of the DB9 connector) will latch to low state until a keyswitched reset occurs.
Power-On reset
The Power-On Reset feature will not allow lasing to restart after a power failure or shutdown has oc-
curred until the Keyswitch or Remote Keyswitch is first cycled off (open circuit condition) and then back
on (closed circuit). Power-On Reset is defeated on all OEM versions. OEM customers must provide this
required safety feature elsewhere as part of their equipment integration.
RF Driver IV
RF power is provided by a patented single MOSFET transistor power oscillator operating in a tuned
feedback circuit. The low-impedance MOSFET output is coupled to the relatively high-impedance laser
tube electrode by a ceramic-substrate micro-strip transmission line integral to the RF circuit board.
RF rise time is about 1 µs to deliver a striking voltage of over 500 V peak to the discharge electrodes. A
pulse-stretching network on the control board widens the incoming Command input so that the tickle
pulses delivered from the RF Driver are sufficient to provide a plasma ready state without emission.
The RF drive is not centered on a frequency authorized for significant incidental radiation (ISM bands
around 27 and 40 MHz). The power module must therefore be shielded effectively which is accomplished
by integrating the plasma tube and drive into a single assembly. Refer to Figure 3-4 for the RF Driver IV
circuit schematic.
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