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

UG:107 vicorpower.com Applications Engineering: 800 927.9474 Page 23
External Trim (J2-1)
Output voltage can be trimmed using an optional factory-installed Trim potentiometer
or with the Trim pin (see Figure 11). The Trim potentiometer is located on the
ConverterPAC. If the Trim potentiometer has not been ordered, the Trim pin must
be used. When using the Trim pin, the Trim limits are determined by the DC to DC
converter used on the ConverterPAC. Maximum Trim ranges are 10% above the
nominal converter voltage and 50% below the nominal converter voltage
(except 10 V, 12 V and 15 V outputs which are 10% below nominal) as measured from
the output studs or output connector of the power supply.
Note: The combined effects of module trim up, remote sense and dynamic load step may cause the
module to trip OVP. (See page 7 for information on restart).
The Trim pin on J2 can be used to control the output voltage. It is referenced to the
-Sense pin on J2 and can be controlled by either a resistor network or an external
voltage source. To increase an output voltage above its nominal, it is necessary to
increase the voltage at the Trim pin above the internal reference voltage (Vref). The
reverse is true to decrease an output voltage.
Note: Converters are sometimes pretrimmed at the factory if a nonstandard output
voltage is requested. Standard voltages include 2 V, 3.3 V, 5 V, 10 V, 12 V, 15 V, 24 V,
28 V, and 48 V. If using a nonstandard voltage, or if a ConverterPAC is ordered with a
Trim option, the resistor calculations will differ from those below. Please consult the
factory for assistance.
Output Module V
ref
R
TH
VE-200/VE-J00 ³3.3 V 2.5 V 10.0 kW
VE-200/VE-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
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