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ultrabrains
Joined: 14 Feb 2007
Posts: 113
Helped: 8
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 07 Mar 2008 17:23 LM317 output Currrent |
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| hey can anyone tell me how to increase the output current of a LM317 Voltage regulator to say 10 Amps or even more
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mister_rf
Joined: 27 Feb 2008
Posts: 238
Helped: 57
Location: Romania
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ultrabrains
Joined: 14 Feb 2007
Posts: 113
Helped: 8
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| 07 Mar 2008 18:34 Re: LM317 output Currrent |
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Thanks for the link.
How can i use a mosfet to incresae the current instead of transistors (2N3055) since mosfets handle higher currents and dissipate less heat.
thanks
circuit attached.
Added after 11 minutes:
the circuit diagram
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mister_rf
Joined: 27 Feb 2008
Posts: 238
Helped: 57
Location: Romania
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| 07 Mar 2008 18:58 Re: LM317 output Currrent |
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| If the MOSFET transistors are used in a linear mode, you'll have the same heat dissipated compare to the bipolar ones.
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ultrabrains
Joined: 14 Feb 2007
Posts: 113
Helped: 8
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| 07 Mar 2008 19:07 LM317 output Currrent |
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can you give a circuit to illustrate using MOSFET transistors in a linear mode.
i know small mosfets handle very high currents
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mister_rf
Joined: 27 Feb 2008
Posts: 238
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Location: Romania
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laktronics
Joined: 06 Jan 2007
Posts: 725
Helped: 122
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| 07 Mar 2008 21:01 Re: LM317 output Currrent |
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Hi,
What about an LM396 in its place?
Regards,
Laktronics
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chip2000
Joined: 01 Mar 2008
Posts: 6
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| 07 Mar 2008 21:17 Re: LM317 output Currrent |
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Its better to use L200 with external transistors because in most circuits that use lm317 with external transistors there is no current protection for the external transistors.
In L200 with external transistors there is current protection. You will find circuits with L200 in www.st.com Just download the datasheet and the application note
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ultrabrains
Joined: 14 Feb 2007
Posts: 113
Helped: 8
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| 07 Mar 2008 22:54 LM317 output Currrent |
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what is the implication of no current protection if lm317 is used.
L200 is not available here.
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Sinisa
Joined: 03 Mar 2003
Posts: 204
Helped: 37
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| 07 Mar 2008 23:38 Re: LM317 output Currrent |
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There is no advantage in using LM317 when having external transistors for higher current. Use LM723 with NPN transistors you can find . It is not the best IC's arround, but is one of the most used IC's and I would be suprised if you can't find one.
There are tons and tons of circuits on the net with this IC. If you post supply specs you are trying to build, we could help you more.
Click helped me if I did!
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mister_rf
Joined: 27 Feb 2008
Posts: 238
Helped: 57
Location: Romania
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| 08 Mar 2008 0:55 Re: LM317 output Currrent |
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For a supplementary current protection you can use this idea presented in the schematics attached and using external transistor you need to combine the schematics. 
The only problems for all the schematics are related to system efficiency.
Starting 2-3 amps the dissipated heat will increase dramatically and the useless power consumption from power line is huge.
As practical solution is to use a dc-dc step down schematics instead. There’s a lot of IC you can use.
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ultrabrains
Joined: 14 Feb 2007
Posts: 113
Helped: 8
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| 10 Mar 2008 10:24 LM317 output Currrent |
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How do i use a dc-dc step down schematics instead, like i earlier said i was looking for a way to generate a regulated volage say 5v - 15v which i know lm317 can do but the challenge is simply generating more current say 5A - infinity based on the addition of a mosfet since we have mosfets that handle as high as 75Amps.
So if there is another way out( dc-dc step down schematics) let me know.
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ultrabrains
Joined: 14 Feb 2007
Posts: 113
Helped: 8
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| 18 Apr 2008 18:21 LM317 output Currrent |
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still waiting for a response please:
How do i use a dc-dc step down schematics instead, like i earlier said i was looking for a way to generate a regulated volage say 5v - 15v which i know lm317 can do but the challenge is simply generating more current say 5A - 20A based on the addition of a mosfet since we have mosfets that handle as high as 75Amps.
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analogkid
Joined: 01 May 2008
Posts: 7
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| 01 May 2008 15:15 LM317 output Currrent |
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I think you're confusing the switching performance of power mosfets with their lack-of-advantages in linear circuits. Very small MOSFETs handle very large currents, but ONLY when operated in a pulse mode. That is, either saturated or off, never in the linear active region. I use a 75A MOSFET in a 25A switch circuit, and it generates less than 3W of heat. But if that same part were in your application, with 2.5V across it, it would generate over 60W of heat and immediately fail.
Infinity is an impractical design goal. What is the max output current you need to deliver?
ak
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zlatkoMM
Joined: 04 Apr 2008
Posts: 90
Helped: 2
Location: Croatia
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| 12 May 2008 15:45 Re: LM317 output Currrent |
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Bravo mister_rf for good shematic of protection.
People just slow down , LM 317 in classic plastic package TO 220 deliver
only 1.5 A maximum on cca max 24V.
Special type of 317 in metal case has same voltage limit but
has max 5A output.
If you wannt i will send you shematic with transistor without 317
wich has better stability then this chip.
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