Thermal regulation

LM137 - LM337

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Thermal regulation

When power is dissipated in an IC, a temperature gradient occurs across the IC chip

affecting the individual IC circuit components. With an IC regulator, this gradient can be

especially severe since power dissipation is large.

Thermal regulation is the effect of these temperature gradients on output voltage (in

percentage output change) per watt of power change in a specified time. Thermal regulation

error is independent of electrical regulation or temperature coefficient, and occurs within 5

ms to 50 ms after a change in power dissipation. Thermal regulation depends on IC layout

as well as electrical design. The thermal regulation of a voltage regulator is defined as the

The LM137 specification is 0.02 %/W max. In Figure 1, a typical LM337’s output drifts only 3

thus well inside the specification limit of 0.02 %/W x 10 W = 0.2% max. When the 10 W

pulse is ended the thermal regulation again shows a 3 mV step as the LM137 chip cools off.

Note that the load regulation error of about 8 mV (0.08 %) is additional to the thermal

regulation error.

In Figure 2, when the 10 W pulse is applied for 100 ms, the output drifts only slightly beyond

the drift in the first 10 ms and the thermal error stays well within 0.1% (10 mV).