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LM338K Fiches technique(PDF) 7 Page - STMicroelectronics |
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LM338K Fiches technique(HTML) 7 Page - STMicroelectronics |
7 / 12 page will be 0.05 Ω (1 + R2/R1) or in this case, 11.5 times worse. Figure 2 shows the effect of resistance between the regulator and 140 Ω set resistor. With the TO-3 package, it is easy to minimize the re- sistance from the case to the set resistor, by using 2 separate leads to the case. The ground of R2 can be returned near the ground of the load to provide remote ground sensing and improve load regula- tion. PROTECTION DIODES When external capacitors are used with any IC regu- lator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most Figure 2 : Regulator with Line Resistance in Out- put Lead. 20 µF 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 100 µF 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 50 Ω resistor which limits the peak discharge current. No protec- tion is needed for output voltages of 25V or less and 10 µF capacitance. Figure 3 shows an LM338 with protection diodes included for use with outputs greater than 25V and high values of output capacit- ance. Figure 3 : Regulator with Protection Diodes. LM138-LM238-LM338 7/12 |
Numéro de pièce similaire - LM338K |
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Description similaire - LM338K |
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