6

LT1123

5.5V

120

Ω

43

Ω

––

Power (LT1123)

0.05W

0.14W

––

0.12W

0.32W

––

6.0V

150

Ω

51

Ω

20

Ω

Power (LT1123)

0.05W

0.15W

0.37W

0.13W

0.35W

0.76W

7.0V

180

Ω

75

Ω

27

Ω

Power (LT1123)

0.06W

0.14W

0.38W

0.16W

0.36W

0.89W

8.0V

240

Ω

91

Ω

36

Ω

Power (LT1123)

0.06W

0.15W

0.38W

0.17W

0.42W

0.97W

9.0V

270

Ω

110

Ω

43

Ω

Power (LT1123)

0.20W

0.16W

0.41W

0.07W

0.47W

1.11W

10.0V

330

Ω

130

Ω

51

Ω

Power (LT1123)

0.22W

0.17W

0.43W

0.07W

0.52W

1.25W

INPUT

VOLTAGE

0 – 4A

0.75V

OUTPUT CURRENT:

DROPOUT VOLTAGE:

0 – 1A

0.3V

0 – 2A

0.4V

short. This is possible in circuits where an overload is

unlikely and the input voltage and drive requirements are

low. See the section on Thermal Considerations for more

information.

S

APPLICATI

I FOR ATIO

of drive current that will give the required value of output

current. For circuits using the MJE1123 as a pass transis-

tor this can be done using the graph of Dropout Voltage vs

Output Current (Figure 2). For example, 20mA of drive

current will guarantee a dropout voltage of 0.3V at 1A of

output current. For circuits using transistors other than

the MJE1123 the user must characterize the transistor to

determine the drive current requirements. In general it is

recommended that the user choose the lowest value of

drive current that will satisfy the output current require-

ments. This will minimize the stress on circuit compo-

nents during overload conditions.

required drive current and the minimum input voltage.

Curves are shown for 20mA, 50mA, and 120mA drive

current corresponding to the specified base drive currents

for the MJE1123. The data for the curves was generated

using the following formula:

PNP pass transistor

LT1123

6

8

1k

LT1123 F04

10

100

715

14

13

12

11

10

9

5

The following assumptions were made in calculating the

data for the curves. Resistors are 5% tolerance and the

values shown on the curve are nominal.

For 20mA drive current assume:

For 50mA drive current assume:

For 120mA drive current assume:

current. The chart includes a number for power dissipa-