AN533

Through-hole packages

5/22

Figure 2.

Thermal equivalent diagram

1.1.5

TRIAC with external heatsink

If the estimated junction temperature is higher than the maximum junction temperature

specified in the datasheet, a heatsink has to be used.

Recommendation: this calculation has to be made in the worst case scenario i.e with the

maximum dissipated power, load and line voltage dispersions. We have to consider the

maximum ambient temperature around the component i.e. inside the box where the TRIAC

is located.

The same approach as presented in the previous section allows a suitable heatsink to be

defined. Figure 3 shows the thermal equivalent diagram.

Figure 3.

Thermal equivalent diagram with external heatsink

Junction

Ambient air

Tj

Rth(j-a)

Ta

Junction

Heatsink

Ambient air

Tj

Rth(j-c)

Tc

Rth(c-h)

Th

Rth(h-a)

Ta

Case