поискавой системы для электроныых деталей |
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LM340K127812P+ датащи(PDF) 11 Page - National Semiconductor (TI) |
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LM340K127812P+ датащи(HTML) 11 Page - National Semiconductor (TI) |
11 / 17 page Application Hints The LM340/LM78XX series is designed with thermal protec- tion, output short-circuit protection and output transistor safe area protection. However, as with any IC regulator, it be- comes necessary to take precautions to assure that the regulator is not inadvertently damaged. The following de- scribes possible misapplications and methods to prevent damage to the regulator. SHORTING THE REGULATOR INPUT When using large capacitors at the output of these regula- tors, a protection diode connected input to output (Figure 1) may be required if the input is shorted to ground. Without the protection diode, an input short will cause the input to rapidly approach ground potential, while the output remains near the initial V OUTbecause of the stored charge in the large output capacitor. The capacitor will then discharge through a large internal input to output diode and parasitic transistors. If the energy released by the capacitor is large enough, this diode, low current metal and the regulator will be destroyed. The fast diode in Figure 1 will shunt most of the capacitors discharge current around the regulator. Generally no protec- tion diode is required for values of output capacitance ≤ 10 µF. RAISING THE OUTPUT VOLTAGE ABOVE THE INPUT VOLTAGE Since the output of the device does not sink current, forcing the output high can cause damage to internal low current paths in a manner similar to that just described in the “Short- ing the Regulator Input” section. REGULATOR FLOATING GROUND (Figure 2) When the ground pin alone becomes disconnected, the output approaches the unregulated input, causing possible damage to other circuits connected to V OUT. If ground is reconnected with power “ON”, damage may also occur to the regulator. This fault is most likely to occur when plugging in regulators or modules with on card regulators into powered up sockets. Power should be turned off first, thermal limit ceases operating, or ground should be connected first if power must be left on. TRANSIENT VOLTAGES If transients exceed the maximum rated input voltage of the device, or reach more than 0.8V below ground and have sufficient energy, they will damage the regulator. The solu- tion is to use a large input capacitor, a series input break- down diode, a choke, a transient suppressor or a combina- tion of these. When a value for θ (H–A) is found using the equation shown, a heatsink must be selected that has a value that is less than or equal to this number. θ (H–A) is specified numerically by the heatsink manufacturer in this catalog, or shown in a curve that plots temperature rise vs power dissipation for the heatsink. 00778108 FIGURE 1. Input Short 00778109 FIGURE 2. Regulator Floating Ground 00778110 FIGURE 3. Transients www.national.com 11 |
Аналогичный номер детали - LM340K127812P+ |
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Аналогичное описание - LM340K127812P+ |
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