Vicor Constant Current (CC) Demonstration Board User Manual
Page 5
UG:007
vicorpower.com
Applications Engineering: 800 927.9474
Page 5
A.
Auxiliary voltage (VH): The op amp is powered using the VH pin. This pin is a 9 V ±0.3 V
regulated voltage capable of sourcing up to 5 mA. Do not exceed the current rating
for VH. Exceeding the current limit will render the unit inoperative. To increase VH
capability an external circuit scheme using a power transistor can be used as described in
application note
B.
Secondary control (SC): The output of the comparator op amp (U02B) is connected to the
SC pin. This pin will be driven high to drive the PRM output voltage high and vice versa.
The resistor divider formed by (R23 & R30) controls the maximum voltage at the input of
this SC pin. The output of the comparator is about 9 V. Care must be taken when selecting
values different than the recommended (R23 & R30). Please refer to the application note
C.
Output set resistor (R27): This pin defines the maximum output voltage of the PRM when
the error amplifier output drives the SC pin to its maximum. The combination of both
resistors (R27 & R8) forms the R
OS
resistor required to operate the PRM. Reducing the
R
OS
resistor by turning the potentiometer (R8) clockwise will increase the maximum
output voltage. The Fixed resistor (R27) value is chosen to ensure a maximum output
voltage of 55 V. Please refer to the
for more details on
how to choose the appropriate R
OS
value for the desired PRM maximum output voltage.
D.
VTM control pin (VC): This PRM output pin provides a 10 ms pulse during start up enabling
the downstream VTM. VC is connected to pin (3 & 4) on (J01) connector.
2.1.3 Test Points
1.
Input & output Kelvin test points –IN, +IN (TP1 & TP3) and –OUT, +OUT (TP7 & TP8):
These input/output access points of the PRM enable accurate efficiency measurements of
the VI Chip independent of the interconnection losses.
2.
PC (TP3): Test point primary control signal. During normal operation this pin is internally
pulled high to 5 V. Drive this pin low by moving (SW01) to the OFF position to disable the
PRM output. This pin will pulsate under fault conditions.
3.
V
SENSE
(TP4): Test point voltage sense serves to show the output voltage of the difference
amplifier (U02A). This voltage is proportional to the actual PRM-sensed output current.
The constant of proportionality is equal to the difference amplifier gain formed by the
resistors (R16-R18). If the recommended gain of 100 is used in combination with the
10 m
Ω sense resistor the outcome is a one-to-one relationship between the measured
voltage at this test point and the PRM output current. (V
SENSE
= R
SENCE
x Gain x I
OUT
_
PRM
)
4.
V
REF
(TP5): Test point voltage reference value is being compared with the sensed voltage
V
SENSE
. Op amp B is providing an output voltage to the SC pin in order to retain V
SENSE
=
V
REF
= I
OUT
_
PRM
assuming that R
SENSE
x Gain = 1. Turn the potentiometer (R10)
clockwise to increase the required output current set point.
5.
SG (TP6): Test point signal ground is the ground reference for the internal control IC.
6.
Output voltage oscilloscope probe jack (J02): Accepts most oscilloscope probes and
enables precision measurement of the output voltage ripple.