3/3
VEFT1-SMT Dual Output Series Dc-Dc Converter
Rev. 11-2005
Application Notes:
- Input filtering
To reduce the reflected ripple current and minimize
EMI, especially when the converter input is more
than 2” away from the DC source, it is recommended
to connect a low ESR electrolytic capacitor between
Vin and Gnd. The values suggested are as shown in
Table 1. If additional filtering is required, the
capacitance may be increased, or expanded to an LC
network as shown in Figure 1.
- Minimum loading
The converter needs a minimum of 10% loading to
maintain output regulation. Operation under no-load
conditions will not cause immediate damages but
may reduce reliability, and cause performance not to
meet specifications.
- Regulation
With a semi-regulated design, the converter’s output
voltage varies with load current and will change
proportionally to the input voltage. If regulated
output is needed, an external regulator can be used
as shown in Figure 2.
Table 1
Input Voltage
5V
12 V
15 V
24 V
- Output filtering
An output capacitor is needed to meet output ripple
requirements as shown in Table 2.
Output capacitance may be increased for additional
filtering, but should not exeed 10µF or expanded to
an LC network as in Figure 1.
External Input Capacitance
4.7 µF
2.2 µF
2.2 µF
1.0 µF
- Protection
The converter has minimal protection against input
over-voltage or output over-load, and may be
permanently damaged if exposed to these conditions.
An input clamping device can be used for input
voltage limiting. An input fuse or an output fuse
can also be used to protect against over-loading.
- Dual outputs used as a single output
The +Vout and -Vout can be used to obtain a single
output that is the sum of the two outputs. In this
case, the COM pin shouldn’t be used.
- External Regulator
An external 3-terminal regulator can be connected
to the output of the converter to achieve full
regulation. Make sure the converter’s output voltage
provides sufficient head room for the regulator. An
additional benefit is that the built-in protection
features in the regulator, such as OCP, OTP, etc, will
protect the converter also. In a complimentory
supply, a negative output regulator must be used to
achieve the negative regulated output.
+Vout
Table 2
Vout
5V
9V
12 V
15 V
24 V
External Ouput Capacitance
10 µF
4.7 µF
2.2 µF
1 µF
0.47 µF
+Vin
-Vin
+Vin
C
L
L
REG
REG
DC DC
DC DC
+Vout
C
L
C
REG
REG
COM
-Vout
+Vout
COM
REG
REG
-Vin
DC DC
<Figure 1>
COM
-Vout
+Vin
-Vin
DC DC
DC DC
-Vout
V-Infinity, LLC, 20050 SW 112th Ave., Tualatin, OR 97062
www.v-infinity.com
1-866-372-1258
CUI [ CUI INC ]
