20μF capacitors have low enough internal series re- sistance to deliver 20A spikes when shorted. Al- though the surge is short, there is enough energy to damage parts of the IC.
When an output capacitor is connected to a regula- tor and the input is shorted, the output capacitor will discharge into the output of the regulator. The dis- charge current depends on the value of the capaci- tor, the output voltage of the regulator, and the rate of decrease of VI. In the LM338 this discharge path is through a large junction that is able to sustain 25A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 100μF or less at output of 15V or less, there is no need to use diodes.
The bypass capacitor on the adjustment terminal can discharge through a low current junction. Dis- charge occurs when either the input or output is shorted. Internal to the LM338 is a 50Ω resistor which limits the peak discharge current. No protec- tion is needed for output voltages of 25V or less and 10μF capacitance. Figure 3 shows an LM338 with protection diodes included for use with outputs greater than 25V and high values of output capacit- ance