LM317 Adjustable Voltage current Boost Power Supply
YouTube video Current Boost LM317 Adj. Power Supply
The LM317 is an inexpensive solution to simple variable power supplies. I have several surplus laptop power supplies often rated at 19V at several amps. The LM317 has a low current rating that limits its use. This is the simple solution.
In Fig. 1 I have a LM317 combined with a MJ2955 PNP pass transistor. As rated at an "excess" of 1.5 amps. By 0.5 amps the device is getting hot. The above test circuit supplied 1 amp while 95% of current passed through Q1.
The voltage control properties of the LM317 was normal. The control of the output voltage remained the same. A 10-Ohm resistor across Q1 base-emitter junction is key to current control. Let us take a closer look.
Refer to Fig. 2. Suppose the circuit is set for 10-volts and a current of 50mA. Rb current passing through the 10-Ohm resistor produces a voltage drop of 0.5V.
This is not enough to turn on Q1 while the LM317 supplies the load current. The heat sink on the LM317 is warm.
Refer to Fig. 3. The output voltage is still 10-volts, but the supply current I is 1 amp. The 10-Ohm resistor Rb drops 0.7 volts turning on Q1.
Most of the supply current flows though Q1 emitter-collector circuit. Most of the current though Rb flow through Q1 base-collector circuit.
About LM317 supplies 50mA while Q1 supplies 950mA. The LM317 heat sink is warm while Q1 heat sink get warm.
One can change the value of Rb to change the turn-on point of Q1.
The more current needed by the load the more Q1 conducts. The excess current bypasses the LM317.
- Experiments with TL431 Shunt Regulator
- TL431 Precision Current Regulator Circuits
- TL431 Based Current Limiter Constant Current Source Circuits
- TL431 Shunt Regulator Circuits
- Comparing ATmega328 Based Transistor Checkers
- Basic MOSFET Transistor Test Circuits
- High Voltage MOSFET Switching Circuits
- LM317 Adjustable Voltage current Boost Power Supply
- LM317 High Power Constant Current Source Circuit
- Constant Current Circuits with the LM334
- LM334 Constant Current Source with Resistive Sensors
- LM317 Constant Current Source Circuits
- Introduction Hall Effect Switches, Sensors, and Circuits
- Using Ratiometric Hall Effect Sensors
- Pulse Width Modulation Power Control for Microcontrollers
- Introduction to PIC12F683 Programming
- Basic Transistor Driver Circuits for Micro-Controllers
- Opto-Isolated Transistor Drivers for Micro-Controllers
- Introduction to Python Bitwise Operations
- Python Bitwise Operations by Example
- ULN2003A Darlington Transistor Array with Circuit Examples
- Tutorial Using TIP120 and TIP125 Power Darlington Transistors
- Driving 2N3055-MJ2955 Power Transistors with Darlington Transistors
- Understanding Bipolar Transistor Switches
- N-Channel Power MOSFET Switching Tutorial
- P-Channel Power MOSFET Switch Tutorial
- H-Bridge Motor Control with Power MOSFETS
- More Power MOSFET H-Bridge Circuit Examples
- Build a High Power Transistor H-Bridge Motor Control
New January 2018:
- Arduino Nano Test Template
- Arduino Solid State Relay Motor Enable Control
- Arduino Blink LED Tutorial
- Arduino SSR Power Enable Program
- SSR Based High Voltage H-Bridge
- Arduino H-Bridge Motor Control Program with LCD Display
- Arduino XOR Blinks LED
- Arduino IF Statement Code Examples
- Arduino Motor Control Program Using IF
- LM317 Adjustable Voltage Source Current Boost
- Geiger Counter Adventures in Radioactivity
- Introduction to Geiger-Mueller Counters and Electronics
- Astable CD4047 Geiger Counter Power Supply
- CD4047 Monostable Multivibrator Circuit
- Getting Real About Radiation Myths and Hazards
- Uranium Hype-Facts and Virginia Uranium
- Uranium Basics and Isotopes
- Climate Change, Climate Scams, and Volcanoes
- Technology is Why the Jobs are Not Coming Back
- Off-the-Shelf Technology for Space Exploration