VEFT1-SMT Dual Output Series Dc-Dc Converter

Rev. 11-2005

3 / 3

V-Infinity, LLC, 20050 SW 112th Ave., Tualatin, OR 97062

www.v-infinity.com

1-866-372-1258

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.

Input Voltage

External Input Capacitance

4.7 µF

5 V

12 V

2.2 µF

15 V

2.2 µF

24 V

1.0 µF

Table 1

- 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.

Vout

External Ouput Capacitance

10 µF

5 V

9 V

4.7 µF

12 V

2.2 µF

15 V

1 µF

24 V

0.47 µF

Table 2

<Figure 1>

+Vin

-Vin

+Vout

COM

DC

C

L

L

DC

L

C

C

-Vout

+Vin

-Vin

+Vin

-Vin

REG

+Vout

-Vout

COM

+Vout

DC

DC

DC

DC

REG

REG

COM

-Vout

REG

DC DC

DC DC

REG

REG

- 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.

- 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.