# Alternative Transistors for LM317 High Current Voltage Regulator Circuit

#### sribasu

Joined May 10, 2017
18
Hi,
I am referring the below circuit diagram to make a High Current Linear Voltage Regulator circuit. This circuit is given in LM317's datasheet.

I need the regulator circuit to handle no more than 5 AMP Output Current. I find TIP73 a little overestimate for this current. Moreover, I do not have this transistor handy. For 5 AMP output, what would be the alternatives for TIP73 and 2N2905 transistors in this circuit?
Can I replace them with 2N3055/TIP3055 and TIP42/MJE2955 respectively? Would 2N3055/TIP3055 cause any interference to the LM317 to regulate the output voltage?

#### Dodgydave

Joined Jun 22, 2012
10,061
Yes your selection of alternative transistors will work just as well.

I would use the MJE3055 in a To220 case.

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#### sribasu

Joined May 10, 2017
18
Yes your selection of alternative transistors will work just as well.
Thanks Dodgydave for your response. I have a followup question. I am new to Electronics. I learned the other day that 2N3055 has high leakage, so do I need to attach a load everytime (just like the one shown in the diagram) to measure the output voltage?
If yes, what is a practical value and wattage rating of the recommended load resistor to use when measuring the output voltage?

#### Dodgydave

Joined Jun 22, 2012
10,061
The Lm317 needs a minimum of 10mA load, i would use a 100ohm 10W load resistor, and use the MJE3055 transistor.

#### crutschow

Joined Mar 14, 2008
27,898
Make sure the 3055 is mounted on a good heatsink as it will dissipate ≈(Vin-Vout)*Iout watts.

Also that circuit is not short-circuit protected.

#### bertz

Joined Nov 11, 2013
327
Hi,
I am referring the below circuit diagram to make a High Current Linear Voltage Regulator circuit. This circuit is given in LM317's datasheet.

I need the regulator circuit to handle no more than 5 AMP Output Current. I find TIP73 a little overestimate for this current. Moreover, I do not have this transistor handy. For 5 AMP output, what would be the alternatives for TIP73 and 2N2905 transistors in this circuit?
Can I replace them with 2N3055/TIP3055 and TIP42/MJE2955 respectively? Would 2N3055/TIP3055 cause any interference to the LM317 to regulate the output voltage?
The circuit shown will NOT be able to handle 5 amps! In fact it will not even handle 3 amps. You need at least two pass transistors in parallel mounted on a hefty heat sink with fan cooling as shown in the attached photo. The TO-3 case has much better heat dissipation capability than the TO-220.
As Crutschow correctly points out this circuit has no short circuit protection or current limit capability. I suggest you take the time to view this tutorial on power supply design.

#### Picbuster

Joined Dec 2, 2013
1,027
Hi,
I am referring the below circuit diagram to make a High Current Linear Voltage Regulator circuit. This circuit is given in LM317's datasheet.

I need the regulator circuit to handle no more than 5 AMP Output Current. I find TIP73 a little overestimate for this current. Moreover, I do not have this transistor handy. For 5 AMP output, what would be the alternatives for TIP73 and 2N2905 transistors in this circuit?
Can I replace them with 2N3055/TIP3055 and TIP42/MJE2955 respectively? Would 2N3055/TIP3055 cause any interference to the LM317 to regulate the output voltage?
It is, due to efficiency, not useful to use linear power supplies above the 1 Amp.
Advice use a step down see TI's step down pages call simple switches one coil few cap and two resistors.

Picbuster

#### Tegra

Joined May 18, 2017
2
I agree with Picbuster, linear supplies are out of date. A small switcher will be smaller, cheaper to build and actually save a substantial amount in power consumption. (Saving even 1 watt will save $1 a year, your circuit will likely "waste"$20 a year)

T

#### sribasu

Joined May 10, 2017
18
Thanks for replying. Unfortunately I can't use a SMPS for my purpose. I got it working with 2N3055 transistor TO-3 package along with a TIP2955 (I know I could have chosen a smaller one).
Thank you all for responding to my question. I really appreciate your help!

I made a PCB layout of LM317 power supply. Sharing it here, if it helps anyone else!

#### DickCappels

Joined Aug 21, 2008
7,842
Make sure the 3055 is mounted on a good heatsink as it will dissipate ≈(Vin-Vout)*Iout watts.

Also that circuit is not short-circuit protected.
Is the 2N2905 sufficient for limiting the current?