Application Hints

The LM136 series voltage references are much easier to use

than ordinary zener diodes. Their low impedance and wide

operating current range simplify biasing in almost any circuit.

Further, either the breakdown voltage or the temperature co-

efficient can be adjusted to optimize circuit performance.

Figure 1 shows an LM136 with a 10k potentiometer for ad-

justing the reverse breakdown voltage. With the addition of

R1 the breakdown voltage can be adjusted without affecting

the temperature coefficient of the device. The adjustment

range is usually sufficient to adjust for both the initial device

tolerance and inaccuracies in buffer circuitry.

If minimum temperature coefficient is desired, two diodes

can be added in series with the adjustment potentiometer as

shown in

Figure 2. When the device is adjusted to 2.490V

the temperature coefficient is minimized. Almost any silicon

signal diode can be used for this purpose such as a 1N914,

1N4148 or a 1N457. For proper temperature compensation

the diodes should be in the same thermal environment as

the LM136. It is usually sufficient to mount the diodes near

the LM136 on the printed circuit board. The absolute resis-

tance of R1 is not critical and any value from 2k to 20k will

work.

DS005715-28

FIGURE 1. LM136 With Pot for Adjustment

of Breakdown Voltage

DS005715-29

FIGURE 2. Temperature Coefficient Adjustment

Low Cost 2 Amp Switching Regulator

†

DS005715-5

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