SEP 12, 2003 revised to OCT 26, 2006

Page 6 of 8

www.power-one.com

QLS25 DC-DC Series Data Sheet

25A Quarter-Brick

where A and B are constants from the table below,

and ΔV is the absolute value of the desired change

in the output voltage in Volts.

Trim up

Trim down

Model

A

B

A

B

QLS20ZG

3.77

6.81

11.58

9.88

QLS25ZE

2.07

3.92

3.5

5.61

QLS25ZD

1.27

3.92

1.31

4.95

Industry Standard Positive Trim (suffix –T)

The -T option units trim up with a resistor from the

TRIM pin to the +Sense pin and trim down with a

resistor from the TRIM pin to the –Sense pin as

shown in the Figure 9.

Figure 9. QLS25 Series Positive Trim Schematic

The equations below determine the trim resistor

value required to achieve a ΔV change in the output

voltage.

⎟

⎠

⎞

⎜

⎝

⎛

Δ

Δ

+

−

Δ

Δ

+

=

%

%

2

100

%

225

.

1

%)

100

(

11

.

5

V

V

V

V

Vout

R

UP

,k

Ω

⎟

⎠

⎞

⎜

⎝

⎛

−

Δ

=

2

%

100

11

.

5

V

R

DOWN

, k

Ω

where ΔV% is the output voltage change expressed

in percents of the nominal output voltage, Vout.

Notes:

1.

When the output voltage is trimmed up, the output power

from the converter must not exceed its maximum rating. The

power is determined by measuring the output voltage on the

output pins, and multiplying it by the output current.

2.

In order to avoid creating apparent load regulation

degradation, it is important that the trim resistors are

connected directly to the remote sense pins, and not to the

load or to traces going to the load.

3.

The QLS25 Series converters will trim down further than the

10% limit. In general, this is permissible. The user must

confirm that the results are acceptable in the application.

Safety Considerations

The QLS25 Series converters feature 1500 Volt DC

isolation from input to output. The input to output

resistance is greater than 10MOhm.

These

converters are provided with Basic insulation

between input and output circuits according to all

IEC60950 based standards.

Nevertheless, if the

system using the converter needs to receive safety

agency approval, certain rules must be followed in

the design of the system. In particular, all of the

creepage and clearance requirements of the end-use

safety requirements must be observed.

These

documents include UL60950 - CSA60950-00 and

EN60950, although other or additional requirements

may be needed for specific applications.

The QLS25 Series converters have no internal fuse.

The external fuse must be provided to protect the

system from catastrophic failure as shown in

Figure 7. The fuse with a rating not greater than 4A

is recommended. The user can select a lower rating

fuse based upon the highest inrush transient at the

maximum input voltage and the maximum input

current of the converter, which occurs at the

minimum input voltage. Both input traces and the

chassis ground trace (if applicable) must be capable

of conducting a current of 1.5 times the value of the

fuse without opening. The fuse must not be placed

in the grounded input line, if any.

In order for the output of the QLS25 Series converter

to be considered as SELV (Safety Extra Low

Voltage) or TNV-1, according to all IEC60950 based

standards, one of the following requirements must be

met in the system design:

•

If the voltage source feeding the module is SELV

or TNV-2, the output of the converter may be

grounded or ungrounded.

•

If the voltage source feeding the module is ELV,

the output of the converter may be considered

SELV only if the output is grounded per the

requirements of the standard.

•

If the voltage source feeding the module is a

Hazardous Voltage Secondary Circuit, the

voltage source feeding the module must be

provided with at least Basic insulation between

the source to the converter and any hazardous

voltages.

The entire system, including the

QLS25 converter, must pass a dielectric

withstand test for Reinforced insulation. Design

of this type of systems requires expert