Battery Switch With Low Dropout Regulator

In the form of the LT1579 Linear Technology (www.linear-tech.com) has produced a practical battery switch with an integrated low-dropout regulator. In contrast to previous devices no diodes are required. The circuit is available in a 3.3 V version (LT1579CS8-3.3) and in a 5 V version (LT1579CS8-5), both in SO8 SMD packages. There is also an adjustable version and versions in an SO16 package which offer a greater range of control and drive signals. The main battery, whose terminal voltage must be at least 0.4 V higher than the desired output voltage, is connected to pin IN1. The backup battery is connected to pin IN2. The regulated output OUT can deliver a current of up to 300 mA. The LDO regulator part of the IC includes a pass transistor for the main input voltage IN1 and another for the backup battery on IN2.

The IC will switch over to the backup battery when it detects that the pass transistor for the main voltage input is in danger of no longer being able to maintain the required output voltage. The device then smoothly switches over to the backup battery. The open-drain status output BACKUP goes low to indicate when this has occurred. When neither battery is able to maintain the output voltage at the desired level the open-drain output DROPOUT goes low. The LT1579 can operate with input voltages of up to +20 V from the batteries. The regulator output OUT is short-circuit proof. The shutdown input switches off the output; if this feature is not required, the input can simply be left open.

 

 

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How to Increase Current 7805 Voltage Regulator

7805 voltage regulator is one variant of the three terminal Positive Voltage Regulator. IC 7805 operated at maximum load current at a positive fixed voltage 5V 1A, but work on the maximum current will increase the thermal level. Aluminum heatsink is needed to reduce the level of heat, though internally IC 7805 has a thermal over-load protection.

The voltage regulator that works at the maximum rate is an unfavorable condition. Besides the heat level increases, it will likely be fatal if an increase in the load current due to short circuit. A good idea is to increase load current capability by adding an external transistor.

Based on the manual of IC 7805 has given a basic circuit to operate the IC at higher load currents. Download 7805 datasheet manual.

7805 Voltage Regulator Circuit 

In the following circuit to increase 7805 output current up to 3 amperes, must be added a complementary NPN transistor MJ2955. The advantage of this technique is to overcome when there is short-circuit as described above. When there is a voltage drop, then the circuit will reduce the maximum current consumption. So the problem can be solved.

7805 Voltage Regulator Circuit

Transistor BD240C in the DC voltage regulator circuit serves as a current limiting. The transistor is open when the voltage at 10R+0.22R be higher than 0.6-0.7 Volts, which leads to a reduction to zero of the T2 base current. The voltage at which the short-circuit protection starts to act, is given by voltage sum on 0.22R and 10R. Base voltage is determined by resistors 10R and 150R. In this circuit did not happen over-thermal when short-circuit occured, the maximum current was only 0.5 Ampere.

Hope this simple explanation may help in making a higher current-voltage regulator using IC 7805. You can open the manual datasheet of the 7805 voltage regulator for more information.

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