Vicor Autoranging MegaPAC AC-DC Switcher - Manual (Page 19)

UG:106 vicorpower.com Applications Engineering: 800 927.9474 Page 19
Interface Connections (Cont.)
Output Module V
ref
R
TH
VI-200/VI-J00 ³3.3 V 2.50 V 10.0 kW
VI-200/VI-J00 <3.3 V 0.97 V 3.88 kW
Example:
±10% Trim adjust on a 12 V nominal output.
Figure 10 shows a typical variable Trim circuit. Using a 10 k trimpot (R7), the resistor
values for R6 and R8 can be calculated as follows:
V1= V
ref
+ 10% = 2.75 V Given: V
ref
= 2.5 V (see Table 1)
I
R5
= (2.75 V - V
ref
)/R
TH
= (2.75 V - 2.5 V)/10 kW = 25 mA
Setting the bottom limit:
V
R6
= 2.5 V - 10% = 2.25 V
And since I
R5
= I
R6
= 25 mA,
R6 = V
R6
/I
R6
= 2.25 V/25 mA = 90 kW
V
2
= V
1
+ V
R6
= 2.75 V + 2.25 V = 5 V
I
R7
= V
2
/R7 = 5 V/10 kW = 500 mA
I
R8
= I
R7
+ I
R6
= 525 mA
V
R8
= (V
nom
+10%) - V
2
= 13.2 V - 5 V = 8.2 V Given: V
nom
= 12 V
R8 = V
R8
/I
R8
= 8.2 V/525 mA = 15.62 kW
Using the above resistor combination, a 12 V output can be trimmed externally up
to 13.2 V and down to 10.8 V. For further information on external trimming, refer to
Chapter 5 of the Applications Manual or consult the factory for assistance.
CONSULT APPLICATIONS ENGINEERING WHEN TRIMMING OUTPUTS THAT ARE 5 V OR LESS.
Figure 10.
External Trim
(Remote Sense)
Load
+P +Out
J2-2 +Sense
J2-3 -Sense
-P -Out
Use 22-24 AWG Twisted Pair Wires
R5
2.5V
Bandigap
J2-1
R6
R8
R7
To Error
Amplifier
R4
R3
R2
R1
+
+
V
2
V 1
-
-
RTH
Use 22-24 AWG
Twisted Pair Wires
Table 1.
Module Internal Reference
Voltages and Thevenin
Resistances.
End of Life - Not Recommended for New Designs