Scientific 5000 Series, Manual

Page: 49 / 360

3 - THEORY
MODEL 5000 SERIES MANUAL
Version 1.23
3-3
circuit and then applied to the device. The sources are ramped on smoothly and
shutdown at the end of the test cycle. All ranges and load switching is done only
after the sources are shutdown. This facilitates dry contact switching to provide
longest possible relay life.
3.2.1 Hi Source Board
The Hi Source Board drives through the device-under-test (DUT) anode/collector and
returns through monitor resistors for return current measurement. The monitor
resistors are decade precision (R19-28), one of which is switched in the circuit to
determine the current range. When used as a current source, the monitor current
becomes the controlling element. The source is thereby a current source when the
reference voltage input is fixed and reference current is varied. It is a voltage source
when the reference current input is fixed and the reference voltage is varied.
Voltage drive is generated by the amplifier (U1) and buffer transistor drives. Current
limiting is performed by amplifier networks containing U9 and U15. These limit the
current when in voltage drive and control the current when in current drive.
Reference voltages for the current and voltage drives are generated by the Analog
Board via the OUT bus. The sample and hold circuit on the source boards pick their
voltages off the bus in the proper time frame and store them for the test cycle. The
current result is fed to U9, U15 and associated circuitry that controls the source
element.
3.2.2 Lo Source Board
The Lo Source Board drives the base/gate of the device-under-test and operates in
much the same way as the Hi Source Board. In fact, both source boards use the
same printed circuit board with silk-screened identifiers to indicate differences. Notes
on the POWER SOURCE schematic indicate parts differences. The primary
difference in the Lo Source is that its current is monitored at the output rather than
the return side of the source. The Lo Source produces lower voltage and current,
consistent with requirements for base/gate drive. The Lo Source is otherwise
essentially the same as the Hi Source, a buffered power amplifier with both voltage
and current control.
3.2.3 Relay Board
The Relay Board is a group of relays that steer power sources and loads plus monitor
circuits to produce resultant anode to cathode and gate to cathode voltages. Relays
K3, 17, 5, 6 and 7 switch anode loads in and out of the circuit. Relays K20, 21, 22,
23, 11, 12 an 13 control various gate to cathode and anode to cathode loads. All
these relays are set-up automatically for each test according to programmed test
entries. Gains are switched in and out by K18 and K19.
Resultant monitor voltages for anode to cathode and gate to cathode are developed
at U17 output and U10 output respectively. Both are properly buffered to avoid
loading the device-under-test. One or the other is put on the bus for return to the
Analog I/O Board for result decision.
The booster function is contained on the Relay Board for generating voltages above
50 volts. The sep-up transformer is off board and is driven via connector J3.