LM317 Adjustable Regulator: Boosting Current with Power Transistors
LM317 is a versatile adjustable regulator chip known for its output voltage range of 1.25V to 35V. While it can deliver currents up to 1.5A, this may not be sufficient for some power applications. In this article, we explore methods to boost the current using power PNP and NPN pass transistors.
Circuit Analysis
The LM317 is a three-terminal positive-voltage regulator with various protective features. However, its limited output current capacity can be enhanced using pass power transistors.
Current Boosting Using a PNP Power Transistor (MJ2955)
Figure 1 illustrates an adjustable high-current regulator circuit using the MJ2955 transistor. Components like resistors, diodes, and capacitors play crucial roles in regulating the output voltage and current.
Current Boosting Using an NPN Power Transistor (2N3055)
Figure 2 showcases a similar current-boosting circuit utilizing the 2N3055 transistor. Proper component selection and placement are essential for optimal performance.
PCB Board Implementation
For practical testing, the circuits can be implemented on a prototyping board. Figure 3 displays the MJ2955 boosting circuit layout for demonstration purposes.
Test and Measurements
Testing the circuit output is crucial for performance evaluation. Figure 4 exhibits an oscilloscope capture of the output noise/ripple from the MJ2955 current-boosting circuit. Proper PCB design and grounding techniques are recommended for noise reduction.
LM317, MJ2955, and 2N3055 Components for PCB Design
Check out the oscilloscope capture below from the current booster output for a closer look at the performance of these components:
References:
- [1]: LM317 Datasheet: http://www.ti.com/lit/ds/slvs044x/slvs044x.pdf
- [2]: LM317 Library: https://componentsearchengine.com/part.php?partID=299235
- [3]: MJ2955 Datasheet: https://www.mouser.com/datasheet/2/308/2n3055-d-1190033.pdf
- [4]: MJ2955 Library: https://componentsearchengine.com/part.php?partID=697997
- [5]: 2N3055 Datasheet: https://www.onsemi.com/pub/Collateral/2N3055-D.PDF
- [6]: 2N3055 Library: https://componentsearchengine.com/part.php?partID=788620
- [7]: CAD Plugins: https://www.samacsys.com/library-loader-help
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