These voltage regulators are monolithic integrated circuits designed as fixed−voltage regulators for a wide variety of applications including local, on−card regulation. These regulators employ internal current limiting, thermal shutdown, and safe−area compensation. 78 and 79 series voltage regulators are the most common in power supplies and easy to use.
With adequate heatsinking they can deliver output currents in excess of 1.0 A. Although designed primarily as a fixed voltage regulator, these devices can be used with external components to obtain adjustable voltages and current
Standard Voltages are - 5V - 6V - 8V - 9V - 12V - 15V - 18V - 24V
The MC7900 series of fixed output negative voltage regulators are intended as complements to the popular MC7800 series devices. These negative regulators are available in the same seven voltage options as the MC7800 devices.
Common ground is required between the input and the output voltages. The input voltage must remain typically 2.0 V above more negative even during the high point of the input ripple voltage.
All above circuits can be adapted to the negative 7900 regulators circuits. You have to remember PNP transistors are not used in the final output stages. NPN can take the heat and current loads. So it makes your Negative Regulator Boosters a bit complex. The below two circuits have the 7900 regulators playing their negative roles.
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.
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.