Good Will Instrument PSS-2005 User Manual - page 15
PSS-3203/2005 PROGRAMMABLE POWER SUPPLY
USER MANUAL
20
7. THE SYSTEM DIAGRAM AND DESCRIPTION
7-1. Block Diagram
The graph above is the system diagram of PSS -SERIES, Which consists
of Micro Processor Unit (MPU), Digital to Analog Converter (DAC),
Analog Switch Circuit, Reference Voltage Circuit, Driver Circuit,
Control Circuit, Comparator, and etc.
AC
INPUT
TRANSFORMER
RELAY
CONTROL
VOLTAGE
COMPARATOR
CURRENT
COMPARATOR
D TO A
CONVERTER
REFERENCE
ANALOG
SWITCH
AND SAMPLE
HOLD
MICRO
CONTROL
LCM
DISPLAY
KEYBOARD
AUX
RECTIFIER
AND FILTER
SERIES
REGULATOR
AMPLIFIER
OR
GATE
O/P
INTERFACE
RS-232 OR GPIB
PSS-3203/2005 PROGRAMMABLE POWER SUPPLY
USER MANUAL
21
7-2.The Operation of the whole circuit
Each output channel of PSS -series has a reference voltage circuit at
around 2.5V output voltage which can be amplified to 2.5 (1+R314
/(R315+Vr))=2.5(1+12.4K/(7.68K+Vr)) by a non -inverter amplifier.
When Vr=0~500, take its middle value to convert above formula into
6.41V, and treat this as the reference voltage of DAC AD7541. The
AD7541 is a 12 -bit DAC with 6.41V/4095=1.56mV/bit of the resolution.
When the instrument is in C.V. Mode, the MPU will send 3300
counts, 33.00V of output voltage, to DAC, output through analog switch
and Sample Hold circuit, the voltage now is at around
-5.148V( -1.56mVx3300=-5.148V). Then, compare this voltage with the
real output voltage which is retrieved by the voltage sense circuit. As the
entire circuit is a close loop, therefore, the retrieved voltage value will be
followed with the reference voltage of Sample Hold. Besides, the
Comparator output terminal will output a related voltage value to control
the whole output circuit through a driver circuit
? and generate the
required output voltage. The attenuation of the voltage sense circuit is
A=R342/(R342+R335)=4.99K/(4.99K+27.0K) =0.156, and the output
voltage is Vout=5.148/A=5.148/0.156=33.00V
? If the output is affected
by the offset of materials, can use the Vr to make adequate adjustment.