high current CCS using lm317

AndrewT · 14th December 2011, 11:08 AM

Hi,
my searching abilities are proving to be severely incapable.

How do you wire up an lm317 with a booster transistor, so that it operates as a CCS at currents that exceed the 317's 1.5A current rating?

Nisbeth · 14th December 2011, 06:04 PM

Forgive me for stating the obvious, but wouldn't it be easier to just use an LM350/LM338/LT108x with a higher output current rating? This would only work up to the 7.5A of the LT1083 of course.

/U.

palstanturhin · 14th December 2011, 06:52 PM

Why did not adding current boost (pnp) transistor and current limiting transistor (npn) + current limit resistor work?

Check data sheet page 20 for 6V Charger and go add the boost transistor...
Change resistor values as needed...

AndrewT · 14th December 2011, 07:04 PM

A 317 CCS is a two component assembly.
Is starting with voltage regulator and modifying it to add on a current limiter the only way to get a >1.5A CCS?

SY · 14th December 2011, 07:11 PM

Let's say you have a power NPN. Add a resistor in series with the emitter, and take the CCS output from the "far" end of the resistor. Now, connect the collector to the power source, the "in" of the 317 to the power source. Connect the 317's "out" to the transistor base, then the 317's "adj" terminal to the "far" end of the resistor.

The resistor is calculated as i(set)/0.55. That value is approximate, you may have to diddle the resistor value a bit.

AndrewT · 14th December 2011, 07:17 PM

I have drawn that description out.
I will plug board it this PM.
Thanks.

AndrewT · 14th December 2011, 09:26 PM

It works, with just 3 components.
Thanks again.

SY · 14th December 2011, 09:41 PM

No prob. I love simple circuits.

geraldfryjr · 12:28 AM

I just happened to be working on a 0V to 20V regulator to replace one side of my Microanta bench supply that quit working as it uses a UA723 and I don't have one to replace it.

It seems to be working good as a simulation in this configuration as high power CCS.

As a regulator R4 is a .5 ohm for the existing metering and R1 is the load and R5 would be shorted or nonexistent.

Pretty cool as this would/could be the Basis to a bufferd version of Elvee's LM317 Class A amplifier.

Also I used the 1N4002's for the simulation and Diodes of the proper current rating should be substituted for your application.
Without the diodes the output voltage won't go to 0V as a regulator.
I haven't spent much time on this as I just now whipped up the CCS configuration.

Enjoy

jer

14th December 2011, 11:08 AM	#1
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	high current CCS using lm317 Hi, my searching abilities are proving to be severely incapable. How do you wire up an lm317 with a booster transistor, so that it operates as a CCS at currents that exceed the 317's 1.5A current rating? __________________ regards Andrew T.

14th December 2011, 07:04 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	A 317 CCS is a two component assembly. Is starting with voltage regulator and modifying it to add on a current limiter the only way to get a >1.5A CCS? __________________ regards Andrew T.

14th December 2011, 07:11 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Let's say you have a power NPN. Add a resistor in series with the emitter, and take the CCS output from the "far" end of the resistor. Now, connect the collector to the power source, the "in" of the 317 to the power source. Connect the 317's "out" to the transistor base, then the 317's "adj" terminal to the "far" end of the resistor. The resistor is calculated as i(set)/0.55. That value is approximate, you may have to diddle the resistor value a bit. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

14th December 2011, 07:17 PM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I have drawn that description out. I will plug board it this PM. Thanks. __________________ regards Andrew T.

14th December 2011, 09:26 PM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	It works, with just 3 components. Thanks again. __________________ regards Andrew T.


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14th December 2011, 06:04 PM	#2
Nisbeth diyAudio Member Join Date: Jan 2001 Location: Denmark	Forgive me for stating the obvious, but wouldn't it be easier to just use an LM350/LM338/LT108x with a higher output current rating? This would only work up to the 7.5A of the LT1083 of course. /U.

14th December 2011, 06:52 PM	#3
palstanturhin diyAudio Member Join Date: Jun 2011	Why did not adding current boost (pnp) transistor and current limiting transistor (npn) + current limit resistor work? Check data sheet page 20 for 6V Charger and go add the boost transistor... Change resistor values as needed...

14th December 2011, 09:41 PM	#8
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	No prob. I love simple circuits. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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