Adjustable High-Current Regulated Power Supply Using LM317 & series-pass transistors.
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Adjustable High-Current Regulated Power Supply Using LM317 & series-pass transistors.
Transcript of Adjustable High-Current Regulated Power Supply Using LM317 & series-pass transistors.
Adjustable High Current Regulated Power Supply http://www.repairfaq.org/sam/samschem.htm David Subert ([email protected]) This adds a gain stage to improve regulation compared to the circuit in the sect ion: Higher Current Operation and is shown using an adjustable regulator though a fixed regulator could also be used. This is similar to the circuit in the Texa s Instruments LM317 datasheet. Although not specified, I expect this is good for up to 5 A or more depending on the actual voltage difference between input and output and the size of the heat sink used for the power transistor, Q2. Using th is configuration rather than something like an emitter follower provides much be tter regulation since the point of regulation for the LM317 is still the actual output of the circuit. +-------------------.C E.-------+ | Q2 _\___/_ | | 2N3055 | | | | R5 | +---------.E C.------+---/\/\---+ | Q1 _\___/_ 500 | | 2N2905 | | | / R4 | | \ 5K | | / | | R3 | I +-------+ O | 1N4002 Vin (+) o---+-+---/\/\---+---| LM317 |---+----+--+------+-------+---o Vout (+) | 22 +-------+ | | | | | | A / _|_ | | | | \ R1 /_\ D1 | | | | / 120 | | | _|_ C1 | | | +_|_ C2 / --- 10uF +-------+---+---+ --- 47uF \ RL* | | | - | / | \ R2 +_|_ C3 | | | +->/ 5K --- 10uF | | | | \ - | | | | | | | | | Vin(-) o------+---------------+--+-----------+----------+-------+---o Vout (-) * For proper regulation, RL must be low enough in value to guarantee at least a 30 mA current at the selected output voltage. It can be a separate resistor or p art of the actual load. For even higher current operation, multiple power transistors (Q2) can be wired in parallel as a pass-bank with small (e.g., 0.1 ohm) emitter resistors to balan ce the load. In this case, Q1 may need to be a slightly bigger transistor and R4 reduced in value to provide adequate base drive. Details will depend on your pa rticular needs. As with the other circuits, a negative power supply can be constructed by using the appropriate regulator IC, swapping NPN or PNP transistors, and reversing all the polarities of the capacitors and diode.
