Vicor PRM-AL Customer Evaluation Boards - Manual (Page 7)

UG:003 vicorpower.com Applications Engineering: 800 927.9474 Page 7
6.1 Adjust the PRM® Output Voltage Set Point
6.1.1 Make sure that the power is removed from the unit prior
to making adjustment.
6.1.2 Using a DMM (set to measure resistance), probe between SG (Item 3)
and the pad labeled OS located next to the 5 kΩ trim pot R08.
6.1.3 Adjust R08 such that the meter reads ~ 200 Ω. This value added to the
fixed resistor R07 should total ~ 2.3 kΩ. Note: R07 is 1.7 kΩ on the
boards with the MIL-COTS PRM.
6.1.4 One could also probe between SG and the ON side of switch OSV (#5)
and set the total resistance shown to ~ 2.3 kΩ.
6.1.5 Move switch OSF (#6) to the OFF position.
6.1.6 Move switch OSV (#5) to the ON position.
6.1.7 The unit is now ready to provide the desired output voltage set point.
6.1.8 Powering the device on should yield a no-load output voltage of the
nominal specified value.
6.1.9 The output voltage can now be set to the desired value by varying
trim pot OS (R08).
6.1.10 IT MAY BE POSSIBLE TO INADVERTENTLY TRIM THE OUTPUT TOO
HIGH ENABLING THE OVERVOLTAGE PROTECTION CIRCUIT. If this
happens, reduce the impedance of R08. The initial conditions of steps
6.1.2 and 6.1.3 can be used to recover.
6.1.11 The desired output voltage set point can also be achieved by using the
equations in the data sheet and setting the total OS resistance
(R07+R08) to that value and then configuring the switches as above.
6.1.12 Be certain to adhere to the power vs. output voltage curve in the data
sheet to avoid over powering the device!
6.2 Adjusting the Current Limit
6.2.1 Increasing the load beyond the rated maximum may activate the
PRM’s internal current limit (see data sheet for values) feature. Certain
applications may require a lower limit and for those situations we offer
the adjustment feature.
6.2.2 Refer to the data sheet for the resistance vs. limit curve for the desired
limit value. Note: the IL values of resistors installed on this board
(R01+R02: 2 kΩ+100 kΩ) may not cover the entire range of the curve.
6.2.3 The adjustable IL mode is engaged by repositioning the IL switch (#2)
from OFF to ON. (This may be done while the unit is powered.)
6.2.4 Adjusting the IL trim pot will reduce the current limit from the factory
preset limits specified in the data sheet. It is not possible to increase this
limit beyond the factory settings.
6.2.5 To reinstate the factory limit return the IL switch to the OFF position.
6.3 Trimming the output voltage using SC
6.3.1 Once the output voltage has been determined and set using the
OS resistors, it is still possible to trim the output down to 26 V using the
SC control. Adjusting the output in this manner rather than merely
adjusting the output via the OS values provides improved regulation.