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MC78T05C 数据表(PDF) 9 Page - ON Semiconductor |
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MC78T05C 数据表(HTML) 9 Page - ON Semiconductor |
9 / 12 page MC78T00 Series 9 MOTOROLA ANALOG IC DEVICE DATA APPLICATIONS INFORMATION Design Considerations The MC78T00 Series of fixed voltage regulators are designed with Thermal Overload Protection that shuts down the circuit when subjected to an excessive power overload condition, Internal Short Circuit Protection that limits the maximum current the circuit will pass, and Output Transistor Safe–Area Compensation that reduces the output short circuit current as the voltage across the pass transistor is increased. In many low current applications, compensation capacitors are not required. However, it is recommended that the regulator input be bypassed with a capacitor if the regulator is connected to the power supply filter with long wire lengths, or if the output load capacitance is large. An input bypass capacitor should be selected to provide good high frequency characteristics to insure stable operation under all load conditions. A 0.33 µF or larger tantalum, mylar, or other capacitor having low internal impedance at high frequencies should be chosen. The bypass capacitor should be mounted with the shortest possible leads directly across the regulator’s input terminals. Normally good construction techniques should be used to minimize ground loops and lead resistance drops since the regulator has no external sense lead. Figure 14. Current Regulator Figure 15. Adjustable Output Regulator Figure 16. Current Boost Regulator Figure 17. Current Boost With Short Circuit Protection 5.0 V R Input 0.33 µF MC78T05 R IO The MC78T05 regulator can also be used as a current source when connected as above. In order to minimize dissipation the MC78T05 is chosen in this application. Resistor R determines the current as follows: IO = + IB ∆IB ^ 0.7 mA over line, load and Temperature changes For example, a 2.0 A current source would require R to be a 2.5 Ω, 10 W resistor and the output voltage compliance would be the input voltage less 7.0 V. Constant Current to Grounded Load Input Output 1.0k 4 6 7 2 3 – + 0.1 µF 10k MC1741 VO, 8.0 V to 20 V Vin – VO ≥ 2.5 V The addition of an operational amplifier allows adjustment to higher or intermediate values while retaining regulation characteristics. The minimum voltage obtainable with this arrangement is 3.0 V greater than the regulator voltage. 0.33 µF R 0.1 µF Output 1.0 µF The MC78T00 series can be current boosted with a PNP transistor. The 2N4398 provides current to 15 A. Resistor R in conjuction with the VBE of the PNP determines when the pass transistor begins conducting; this circuit is not short circuit proof. Input–output differential voltage minimum is increased by the VBE of the pass transistor. 2N4398 or Equiv MC78TXX MC78TXX Input Rsc 2N4398 or Equiv. Output R MJ2955 or Equiv. 1.0 µF The circuit of Figure 17 can be modified to provide supply protection against short circuits by adding a short circuit sense resistor, RSC, and an additional PNP transistor. The current sensing PNP must be able to handle the short circuit current of the three–terminal regulator. Therefore, an eight–ampere power transistor is specified. MC78T05 IB ^ 3.5 mA XX = 2 digits of type number indicating voltage. XX = 2 digits of type number indicating voltage. |
类似零件编号 - MC78T05C |
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类似说明 - MC78T05C |
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