09-Sept-14

Application Notes

QSB150 350

Thermal Resistance Information

Voltage trim up

Connect trim resistor Rtrim between Trim pin and -Sense pin.

Where:

R trim up/down is the external resistor in k

Ω.Vnomisthenominaloutputvoltage.Vdesisthedesiredoutputvoltage.R1,R2,R3andVr

are internal to the unit and are defined in the table below.

Voltage trim down

Connect trim resistor Rtrim between Trim pin and +Sense pin

Voltage trim up -

Voltage trim up, Connect trim resistor

Rtrim between Trim pin and +Sense pin.

Voltage trim down -

Connect trim resistor Rtrim between Trim pin

and –Sense pin

R trim up =

R2 x R3 (k

Ω)

R2 + R3

-

R1 Vr - Vf

R2

R2 + R3

R trim down =

- R2 (kΩ)

R trim down =

kΩ

- 10.22

511

%

Where:

%=

x 100

R trim up =

kΩ

--

k x

%

511 10.22

%

Where:

%=

x 100

Output Voltage (V)

R1(k

Ω)

R2 (k

Ω)

R3 (k

Ω)

Vr (V)

Vf (V)

3.3 V

3.00

12.0

4.3

1.24

0.46

5.0 V

2.32

3.3

0.0

2.5

0.0

12.0 V

9.10

51.0

5.1

2.5

0.46

15.0 V

12.0

56.0

8.25

2.5

0.46

24.0 V

20.0

100.0

7.5

2.5

0.46

Output Voltage Trim

QSB100, QSB200 & QSB350 Series

Air Flow Rate

Natural Convection

20 ft. / min (0.1 ms)

7.12 °C/W

100 ft./min (0.5 ms)

6.21 °C/W

200 ft./min (1.0 ms)

5.17 °C/W

300 ft./min (1.5 ms)

4.29 °C/W

400 ft./min (2.0 ms)

3.64 °C/W

500 ft./min (2.5 ms)

2.96 °C/W

600 ft./min (3.0 ms)

2.53 °C/W

700 ft./min (3.5 ms)

2.37 °C/W

800 ft./min (4.0 ms)

2.19 °C/W

0

5

10

15

20

25

30

35

40

45

50

0

10

20

30

40

50

60

70

80

90

100

Natural Convection

20 ft./min. (0.1 m/s)

100 ft./min. (0.5 m/s)

200 ft./min. (1.0 m/s)

300 ft./min. (1.5 m/s)

400 ft./min. (2.0 m/s)

500 ft./min. (2.5 m/s)

600 ft./min. (3.0 m/s)

700 ft./min. (3.5 m/s)

800 ft./min. (4.0 m/s)

Ambient Temperature ,Ta (ºC)

Maximum Power Dissipation vs Ambient Temperature and Air Flow without heatsink

Derating Curve

Output Voltage Trim

QSB75 & QSB150 Series

Value

QSB100/200

QSB350

k

1.225

1.24