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MC78M12CTG bảng dữ liệu(PDF) 9 Page - ON Semiconductor |
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MC78M12CTG bảng dữ liệu(HTML) 9 Page - ON Semiconductor |
9 / 16 page MC78M00, MC78M00A Series http://onsemi.com 9 APPLICATIONS INFORMATION Design Considerations The MC78M00/MC78M00A 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 mF 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. 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 2.0 V greater than the regulator voltage. Input MC78M05C Output 0.33 mF 10 k MC1741 7 6 4 1.0 k 0.1 mF 3 2 The MC78M00 series can be current boosted with a PNP transistor. The MJ2955 provides current to 5.0 A. Resistor R in conjunction 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 VBE of the pass transistor. XX = 2 digits of type number indicating voltage. MC78MXXC Input Output R 1.0 mF MJ2955 or Equiv. 1.0 mF The circuit of Figure 12 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, a 4.0 A plastic power transistor is specified. XX = 2 digits of type number indicating voltage. 1.0 mF MC78MXXC MJ2955 or Equiv. Input Output RSC R 2N6049 or Equiv. VO, 7.0 V to 20 V Vin−Vout ≥ 2.0 V * + Figure 10. Current Regulator The MC78M00 regulators can also be used as a current source when connected as above. In order to minimize dissipation the MC78M05C is chosen in this application. Resistor R determines the current as follows: For example, a 500 mA current source would require R to be a 10 W, 10 W resistor and the output voltage compliance would be the input voltage less 7.0 V. IO = 5.0 V R + IIB IIB = 1.5 mA over line and load changes. Input 0.33 mF R IO MC78M05C Constant Current to Grounded Load Figure 11. Adjustable Output Regulator Figure 12. Current Boost Regulator Figure 13. Current Boost with Short Circuit Protection |
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Mô tả tương tự - MC78M12CTG |
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