LM317 Current Boosting Circuits [2N3055, MJ2955]

LM317 Current Boost Circuits using 2N3055 and MJ2955
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#LM317
LM317 is one of the most popular adjustable regulator chips. The output voltage of the regulator can be adjusted from 1.25V to 35V. However, the chip can deliver currents up to 1.5A which is not enough for some power applications. In this article, I will discuss two methods of LM317 current boosting, using power PNP and NPN pass transistors.

According to the LM317 datasheet: “The LM317 [1, 2] device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V. It requires only two external resistors to set the output voltage. The device features a typical line regulation of 0.01% and a typical load regulation of 0.1%. It includes current limiting, thermal overload protection, and safe operating area protection. Overload protection remains functional even if the ADJUST terminal is disconnected.”
This information proves to us that this cheap 3-terminal device is suitable for many applications but it comes with a drawback for power applications and that is the limitation of the regulator’s output current handling (1.5A in the best conditions). This problem can be solved using a pass power transistor.

Current Boosting Using a PNP Power Transistor (MJ2955)
Figure-1 shows the schematic diagram of the circuit. This is an adjustable high current regulator circuit that the output voltage can be adjusted using a 5K potentiometer.

 The 10R resistor defines the Turn-On time of the pass-transistor and by the way, it defines how much current should passe through the LM317 and MJ2955 [3, 4]. Based on this parameter, the power rate of the resistor must be calculated. 1N4007 is a protective diode and 270R resistor provides the necessary ADJ pin’s current. As mentioned earlier, the 5K potentiometer defines the output voltage. 1000uF, 10uF, and 100nF capacitors have used to reduce noises. Don’t forget to install the transistor on a big heatsink.

[A-2] Current Boosting Using an NPN Power Transistor (2N3055)
Figure-2 shows the schematic diagram of the circuit. The 10K resistor at the output draws a small amount of current to avoid the floating output and it helps to stabilize the output voltage. Here 2N3055 [5, 6] plays the role of pass-transistor also.

[MyVanitar]

LM317 is one of the most popular adjustable regulator chips. The output voltage of the regulator can be adjusted from 1.25V to 35V. However, the chip can deliver currents up to 1.5A which is not enough for some power applications. In this video/article, I will discuss two methods of LM317 current boosting, using power PNP and NPN pass transistors.

[Iploac]

Why do some people use a Bd139 along with these two components when creating a circuit to regulate both voltage and current? Does it enable the user to be able to vary the current?

[idiyerbill]

The forum and the schematics was very helpful thank you so much

[Ianistrip]

Hello very great-clever idea.,
I have a question for your current boost by a 2N3055,
in my old circuit power supply 0-25V - 1.5 A, with 2 x LM 317s,
the first Lm317 works as current limiter & from his output the DC voltage
goes to the second LM 317 for voltage adjust 0 to 25 V for output terminal,
does the right conect the transistor 2N3055 to the first LM 317(current limiter)?
and the resistor's pin 10KΩ connect to this LM's out OR to output terminals + & - ?? or not..
(Iam a simple amateur)
Thank you
*I tryed to upload here a schematic by google-drive (to see you what I mean)
but doesn't let me to upload the link here

[sameerk]

Hello from India....Thank you very much Sir for this easy to understand and very helpful video. Subscibed for more.

[MACYNET]

How much is max input Voltage? Also, there is one more capacitor on the scheme than your build circuit

[tylerthompson]

So i am studying how and why heat gets produced by TO-3 transistors (2N3055) how could i deliberately make my 2N3055 produce heat? Not enough heat to destroy the transistor but enough to say its very hot? How would i set it up? Just put higher voltage on the transistor?

[mehmetberkeinan]

Hello, thanks for project. i have some trouble with this schematic potentiometer. When i reach minimum potentiometer is burning. İn schematic potentiometer 5k or with 5k serial resistor ? its my school project and i stuck.. in the output so unregulated i think potentiometer cause that too.

[thTek]

The Maximum Amp draw per gauge of wire Chart, shows that the breadboard kit wire at 24 gauge can only handle 1.154 Amps, which supports the 5 Watt or less theory

[jp]

You are losing voltage in the small lead wires you are using. The LM317 can regulate far better than you demonstrated. The voltage drop on your lead wires must be huge. Good video for newbies. Adding a pass transistor for more current is far cheaper than buying LM338 if you need more than 1.5 amps.

[timecapsule]

I want to output 15 volts from 23 volts. Which resistor should I change and what value? plz help me

[ruslank]

I have 18V 30A transformer. Can I use MJ11032 instead of 2N3055 and possibly replace LM317 with LM350 if need be?

[emmanuelmatewere]

Can i use a 25c1106 npn power transistor?

[blackwinter]

میگم ی مدار حفاظت اتصال کوتاه سراغ نداری؟ بدون رله

[ربيعالصراوي]

Great job bro, i want a circuit diagram please.

[DariusIC]

Is it possible to make the same circuit for LM337 in negative voltage? For a dual power supply.

[Electronic_For_You]

Plise make a video LM317 and 13005 from old cfl lamp to boost the current pliz 🙏🙏🙏🙏

[stoffel]

Thanks for the video. I read your article. You are kind to share this info. Im looking to build a variable dc power (0-48v) supply with 15 to 20 amp current output. a microwave transformer 220v input to 12v output with KBPC 5010 FBR and beafy cap. I dont know how to calculate the capacitor rating that i need though. Then this circuit of your design afterwards with digital V and A readout. Going to need cooling fan also and safety fuse. Im subscribed and you need more subs and likes. Any tips and advice from your side wil be much appreciated. ( im new to electronics by the way, need to learn allot more)