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MC7912CD2TR4G Datasheet(PDF) 9 Page - ON Semiconductor |
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MC7912CD2TR4G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 16 page MC7900 Series http://onsemi.com 9 APPLICATIONS INFORMATION Design Considerations The MC7900 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 capacitor chosen should have an equivalent series resistance of less than 0.7 W. The bypass capacitor should be mounted with the shortest possible leads directly across the regulators 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. Bypassing the output is also recommended. Figure 8. Current Regulator The MC7905, −5.0 V regulator can be used as a constant current source when connected as above. The output current is the sum of resistor R current and quiescent bias current as follows. The quiescent current for this regulator is typically 4.3 mA. The 5.0V regulator was chosen to minimize dissipation and to allow the output voltage to operate to within 6.0 V below the input voltage. IO = 5.0 V + IB −20 V Input MC7905 10 R IO = 200 mA − VO ≤ 10 V 1.0 mF Gnd Gnd + 1.0 mF + R Figure 9. Current Boost Regulator (− 5.0 V @ 4.0 A, with 5.0 A Current Limiting) When a boost transistor is used, short circuit currents are equal to the sum of the series pass and regulator limits, which are measured at 3.2 A and 1.8 A respectively in this case. Series pass limiting is approximately equal to 0.6 V/RSC. Operation beyond this point to the peak current capability of the MC7905C is possible if the regulator is mounted on a heatsink; otherwise thermal shutdown will occur when the additional load current is picked up by the regulator. *Mounted on heatsink. −10 V Input 0.56 0.56 0.56 MJE200* or Equiv 5.6 2N3055* or Equiv MC7905* 1.0 mF −5.0 V Output Gnd Gnd + + 1.0 mF 10 mF + Figure 10. Operational Amplifier Supply ( ±15 @ 1.0 A) The MC7815 and MC7915 positive and negative regulators may be connected as shown to obtain a dual power supply for operational amplifiers. A clamp diode should be used at the output of the MC7815 to prevent potential latch−up problems whenever the output of the positive regulator (MC7815) is drawn below ground with an output current greater than 200 mA. +20 V Input +15 V Output 0.33 mF 1N4001 or Equiv Gnd Gnd 1.0 mF + −20 V Input −15 V Output MC7815 MC7915 + + + 1.0 mF 1.0 mF 1.0 mF |
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