Vicor 4kW MegaPAC-EL AC-DC Switchers - Manual (Page 23)

UG:108 vicorpower.com Applications Engineering: 800 927.9474 Page 23
Interface Connections (Cont.)
Output Module V
ref
R
TH
VI-200/VI-J00 ³3.3 V 2.5 V 10.0 kW
VI-200/VI-J00 <3.3 V 0.97 V 3.88 kW
Maxi (Pre-Defined) 1.23 V 1.0 kW
Maxi (User Defined) 1.23 V Consult Factory
Example:
±10% Trim adjust on a 12 V nominal output.
Figure 11 shows a typical variable Trim circuit. Using a 10k 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 BELOW 5 V.
Figure 11.
External Trim
(Remote Sense)
Load
+Out
+Sense
-Sense
-Out
Use 22-24 AWG Twisted Pair Wires
R5
V Ref
Trim
R6
R8
R7
To Error
Amplifier
R4
R3
R2
R1
+
+
V
2
V 1
-
-
RTH
Use 22-24 AWG Twisted Pair Wires
End of Life - Not Recommended for New Designs