Lambda LL Series Instruction Manual page 8

Constant voltage circuit operation is determined by changes in the load which
cause a change in one input to the voltage comparator. A second input to the com-
parator is a reference voltage that is developed by a constant current of 1 milli-
ampere flowing in divider elements R8, R15 and R16 (as applicable). The comparator
compares the output voltage change with the reference voltage resulting in an error
signal at the output of the comparator.
In constant voltage operation the voltage across R7 is less than the preset
voltage across R6, causing the current comparator to be at cut off. If the load
current decreases, causing a rise in output voltage, the voltage comparator conducts
less and more current flows through the OR gate. This action causes the amplifier
to conduct more heavily, reducing drive current to the base of driver Ql, causing
the series regulator impedance to increase and the output voltage to decrease accord-
ingly.
Current limit circuit operation is determined by changes in the load. The
current comparator samples load current through current sensing resistor R7. When
the voltage drop across R7 increases to the preset voltage reference determined by
R9 and setting of R6, the current comparator conducts. Thus, when the output cur-
rent rating of the unit is exceeded, the current comparator conducts, decreasing
the current through driver Ql, resulting in an increase of voltage across the series
regulator and a decrease of the output voltage, effectively limiting the output cur-
rent to a safe value. The current limit value is determined by resistors R6, R9
and R7.
The following paragraphs apply only to "OV" suffix models.
Overvoltage Protection Circuit, functional description (See OV schematic diagram):
When the power supply increases above the voltage limit value set by the VOLT-
AGE ADJ. controls, Q102 is biased on. Q102 in turn biases Q101 on through resistor
R104 causing 0102 to supply gate current to SCR-101. SCR-101 turns on and an effec-
tive short circuit across the output terminals is attained. This action causes
the voltage at the power supply terminals to drop, protecting the load from exces-
sive supply output voltage. SCR-101 conducts until the power supply is turned off,
or until Fl opens.