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
(Trim Range =
±
120 mV typical)
DS005715-29
FIGURE 2. Temperature Coefficient Adjustment
(Trim Range =
±
70 mV typical)
Low Cost 2 Amp Switching Regulator
†
DS005715-5
*
L1
60 turns
#16
wire on Arnold Core A-254168-2
†
Efficiency
≈
80%
5
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