LM136A-2.5QML, LM136A-2.5QML-SP

SNOSAM3E – JULY 2007 – REVISED APPRIL 2013

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APPLICATION HINTS

The LM136 voltage reference is much easier to use than ordinary zener diodes. It's low impedance and wide

operating current range simplify biasing in almost any circuit. Further, either the breakdown voltage or the

temperature coefficient can be adjusted to optimize circuit performance.

Figure 12 shows an LM136 with a 10k potentiometer for adjusting 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 13. 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 resistance of R1

is not critical and any value from 2k to 20k will work.

Figure 12. LM136 With Pot for Adjustment

of Breakdown Voltage

(Trim Range = ±120 mV typical)

Figure 13. Temperature Coefficient Adjustment

(Trim Range = ±70 mV typical)

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