page
date
6 of 10
04/2011
PART NUMBER:
VHB75W
DESCRIPTION:
half-brick dc-dc converter
7. OUTPUT TRIMMING
(OPTIONAL)
The output voltages are preset to nominal values as indicated by the models table at the factory. If desired, the output voltage may
optionally be trimmed to a different value (+/- 10%) with external resistors and/or potentiometer as shown below.
+Vin
FIGURE 3. TRIMMING WITH
EXTERNAL POTENTIOMETER
+Vo
+S
Trim
-S
10KΩ
Trimpot
R load
-Vin
-Vo
To trim the output voltage with fixed resistors, the output voltage can be calculated as follows.
Trim-Up
+Vin
+Vo
+Vin
Trim-Down
+Vo
R trim-down
Trim
R trim-up
R load
Trim
R load
-Vin
-Vo
-Vin
-Vo
FIGURE 4: TRIM-UP VOLTAGE SETUP
The value of
R
trim-up
is defined as:
FIGURE 5: TRIM-DOWN VOLTAGE SETUP
The value of
R
trim-down
is defined as:
R
trim-up
=
R1 - R2 x (Vo - Vo, nom)
(KΩ)
o
V - Vo, nom
R
trim-down
=
R1 - R2 x (Vo, nom - Vo)
(KΩ)
Vo, nom - Vo
Where:
R
trim-up
is the external resistor in
K
Ω
.
V
o,nom
is the
nominal output voltage.
V
o
is the desired output voltage.
R
1
,
R
2
,
R
3
,
V
r
, and
V
f
are internal to the unit and are defined in
Table 1. For example, to trim-up the output voltage of 5.0V
module (VHB75W-Q48-S5) by 8% to 5.4V,
R
trim-up
is calculated
as follows:
o
V - Vo, nom
= 5.4 - 5.0 = 0.4 V
R1
= 5.8 KΩ
R2
= 8.2 KΩ
5.8 - 8.2 x 0.4
= 6.3 (KΩ)
0.4
Where:
R
trim-down
is the external resistor in
K
Ω
.
V
o,nom
is the
nominal output voltage.
V
o
is the desired output voltage.
R
1
,
R
2
, and
V
r
are internal to the unit and are defined in
Table 1. For example, to trim-up the output voltage of 5.0V
module (VHB75W-Q48-S5) by 8% to 4.6V,
R
trim-down
is calculated
as follows:
Vo, nom - Vo
= 5.0 - 4.6 = 0.4 V
R1
= 5.8 KΩ
R2
= 10.52 KΩ
R
trim-up
=
3.3V
5V
12V
15V
24V
48V
R
trim-down
=
3.3V
5V
12V
15V
24V
48V
5.8 - 10.52 x 0.4
= 3.98 (KΩ)
0.4
Table 1
Ω
3.168
5.8
19.656
25.474
42.33
74.514
Ω
7.2
8.2
13.304
14.76
16.67
13.0476
Table 2
6.18
5.8
86.45
150
430
1569.6
Ω
15
10.52
60.1
94
120
295.527
Ω
20050
SW
112
th
Ave. Tualatin, Oregon
97062
phone
503.612.2300
fax
503.612.2383
www.v-infinity.com
CUI [ CUI INC ]
