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Example:
±10% Trim adjust on a 12V nominal output.
Figure 8 shows a typical variable trim circuit. Using a 10kΩ trimpot (R7),
the resistor values for R6 and R8 can be calculated as follows:
V
1
= V
REF
+ 10% = 2.75V
Given: V
REF
= 2.5V (see Table 2)
I
R5
= (2.75V – V
REF
)/R
TH
= (2.75V – 2.5V)/10kΩ = 25mA
Given: R
TH
= 10kΩ (see Table 2)
Setting the bottom limit:
V
R6
= 2.5V – 10% = 2.25V
And since I
R5
= I
R6
= 25mA,
R6
= V
R6
/I
R6
= 2.25V/25mA = 90kΩ
V
2
= V
1
+ V
R6
= 2.75V + 2.25V = 5V
I
R7
= V
2
/R7 = 5V/10kΩ = 500mA
I
R8
= I
R7
+ I
R6
= 525mA
V
R8
= (V
NOM
+ 10%) – V
2
= 13.2V – 5V = 8.2V
Given: V
NOM
= 12V
R8
= V
R8
/I
R8
= 8.2V/525mA = 15.62kΩ
CONSULT APPLICATIONS ENGINEERING WHEN TRIMMING OUTPUTS BELOW 5V.
Single-Output Power Supplies (Arrays)
Vicor standard configuration for single-output power supplies is to set the left module (as seen from
looking at the power supply output) as the controlling module of the array.
Figure 8
External pin
(Remote Sense)
Load
+P +OUT
S1/S2 J2-2 +SENSE
S1/S2 J2-3 –SENSE
–P –OUT
Use 20 – 22AWG Twisted Pair Wires
2.5V
REF
S1/S2 J2-1
R6
R8
R7
To Error
Amplifier
+
V
2
–
Use 20 – 22AWG Twisted Pair Wires
