Operator`s manual

Example: 10% trim adjust on a 12 V nominal output.
Figure 18 shows a typical variable trim circuit. Using a 1k trimpot (R7), the resistor values for R6 and R8 can
be calculated as follows:
V
1
=V
ref
+ 10% = 1.353V
Given: V
ref
= 1.23V
I
R5
= (1.353V - V
ref
)/R
TH
= (1.353V – 1.23V)/1k = 122A Given: R
TH
= 1k
Setting the bottom limit:
V
R6
= 1.23V – 10% = 1.107V
And since I
R5
= I
R6
= 122A,
R6 = V
R6
/I
R6
= 1.107V/122A = 9.074k
V
2
= V
1
+ V
R6
= 1.353V + 1.107V =2.46V
I
R7
= V
2
/R7 = 2.46V/1k = 2.46mA
I
R8
= I
R7
+ I
R6
= 2.58mA
V
R8
= (V
nom
+ 10%) – V
2
= 13.2V – 2.46V = 10.74V Given: V
nom
= 12V
R8 = V
R8
/I
R8
= 10.74V/2.58mA = 4.162k
Rev. 05/11/2012 Mission Power Solutions [phone] [e-mail] Pg. 11
Badger II Power Supply Operator’s Manual
Output Module V
REF
R
TH
Standard Vicor Maxi, Mini, Micro 1.23 V 1 kΩ
Special Module 1.23 V Consult MPwrS