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LM317 Pass Transistor Regulator

LM317 Pass Transistor RegulatorLM317 Pass Transistor Regulator circuit

Existing LM317T output can be raised using an additional power transistor to share a portion of the total. The amount of current participation is established with a resistor in series with the input of 317 and a resistor placed in series with all issuers with pass transistor. In the figure below, the pass transistor will start conducting when the LM317 reaches about 1 amp of current, due to the voltage drop in the resistance of 0.7 ohms. This limitation occurs in about two amplifiers to LM317 will fall on one.4 volts through ohm resistor and produce a 700 millivolt drop in resistance of 0.3 ohm emitter. Thus, the existing total is limited to a 2 + (.7/.3) = four.three amps.

The input voltage must be around five. five volts higher than the output at full load and heat dissipation at full load would be about 23 watts, so a relatively large heat sink can possibly be needed for both the regulator and pass transistor . The filter capacitor size can be approximately C = IT / E in which this, T is the cycle time by 50 percent (8.33 mS at sixty Hertz), and E is the voltage drop that will occur in 50 percent cycle. To keep the ripple voltage below 1 volt at 4.3 amps, a 36,000 uF capacitor or filter. The power transformer must be massive enough to ensure that the peak input voltage to the regulator is still five.5 volts mentioned above the output at full load, or 17.five volts for an output of 12 volts. This allows a drop of 3 volts through the regulator and a voltage drop 1. through five of the series resistance (0.7 ohm), and a ripple voltage created from the filter capacitor. A larger capacitor filter will reduce the entry requirements, although not significantly.