Aaron's Homepage Forum
Aaron's Homepage Forum
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password
Forgot your Password?

 All Forums
 Electronics
 Power Supply
 power supply
 New Topic  Reply to Topic
 Printer Friendly
Previous Page
Author Previous Topic Topic Next Topic
Page: of 2

hillbillyboy_316
Apprentece

12 Posts

Posted - Dec 15 2009 :  4:08:29 PM  Show Profile  Reply with Quote
the 240 ohm resistor is 0.238 and the 5k pot goes from 0 to 5.44
Go to Top of Page

hillbillyboy_316
Apprentece

12 Posts

Posted - Dec 15 2009 :  4:15:53 PM  Show Profile  Reply with Quote
and the IN voltage to the regulator is 34 volts
Go to Top of Page

hillbillyboy_316
Apprentece

12 Posts

Posted - Dec 15 2009 :  7:11:24 PM  Show Profile  Reply with Quote
im not getting the 1.25 reference voltage off of my regulator im only getting .50 volts
Go to Top of Page

audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 17 2009 :  10:59:31 AM  Show Profile  Reply with Quote
quote:
Originally posted by hillbillyboy_316

the 240 ohm resistor is 0.238

It should be 1000 times higher.

quote:
the 5k pot goes from 0 to 5.44

It should also be 1000 times higher. Maybe it goes to 5.44k ohms and you don't know how to read your meter.

quote:
and the IN voltage to the regulator is 34 volts

That is fine.

quote:
im not getting the 1.25 reference voltage off of my regulator im only getting .50 volts

That is very wrong. It should have 1.2V to 1.3V from the output to the ADJ pin.

I have never used the wrong resistance of 240 ohms with an LM317, LM338 or LM350 so maybe that is what happens when the resistance is too high.
Why don't you use 120 ohms or 100 ohms?

Go to Top of Page

hillbillyboy_316
Apprentece

12 Posts

Posted - Dec 17 2009 :  2:16:42 PM  Show Profile  Reply with Quote
i replaced the lm338k with a lm317t and i get the 1.2 reference volts and i can get 1.2 volts all the way up to 32 volts, would that mean i had a bad lm338k regulator?
Go to Top of Page

audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 17 2009 :  5:31:50 PM  Show Profile  Reply with Quote
Yes, your LM338 is defective.
Go to Top of Page

madnoob
New Member

1 Posts

Posted - Feb 18 2010 :  2:49:11 PM  Show Profile  Send madnoob a Yahoo! Message  Reply with Quote
Hi all! I don' have an lm338 but i have 4 lm350k available. How could i adapt this schematic in order to get about 10amps of current from it at the maximum voltage posible. The transformer i have is 28 volts AC.Thanks in advance!
Go to Top of Page

audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Feb 18 2010 :  3:47:16 PM  Show Profile  Reply with Quote
quote:
Originally posted by madnoob

Hi all! I don' have an lm338 but i have 4 lm350k available. How could i adapt this schematic in order to get about 10amps of current from it at the maximum voltage posible. The transformer i have is 28 volts AC.Thanks in advance!


Your 28V transformer will make an unregulated supply that is too high for the LM350.

The datasheets for the LM350 and LM338 show a 9A and a 15A variable power supply but they use an obsolete opamp. You can probably find an available opamp that will work.
Go to Top of Page

Rod
New Member

Chile
1 Posts

Posted - May 27 2010 :  4:42:36 PM  Show Profile  Reply with Quote
Hi Aaron.
I have a problem with my power supply.
I designed it and it worked fine between 0-40 V, but it only gives 1.7A. The trafo is for 3A, the rectifier 6A and the regulator is a LM 338K (5A). It should give 3A max, but it doesn't.
Any suggestions ??
Help Please ...
1 x LM338K (National - 5A)
1 x Rectifier KBPC610 (6A - 1000V)
1 x Trafo 16x2 3A (China)
1 x C = 4700 uF (electrolitic)
1 x C = 220 uF (electrolitic)
1 x C = 10 uF (electrolitic)
2 x C = 100 nF
1 x R = 150 Ohm
1 x Pot = 4.7 kOhm

Rodrigo
Go to Top of Page

audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - May 27 2010 :  9:03:44 PM  Show Profile  Reply with Quote
Your 32VAC transformer has a peak voltage of 45.3V and the bridge rectifier charges the main filter capacitor to 43.3VDC when the load is 2.1ADC. The 3A transformer is overloaded when the DC current is more than 2.1A.

The LM338 has a minimum output current of 5A only when its Vin - Vout= 10V or less. So your power supply produces 5A only when its output voltage is from 33.3V to 43.3V.
When the output voltage is set to 13.3V or less then its typical max current is 1A but it could be less.
Go to Top of Page

Hardeen
New Member

2 Posts

Posted - May 14 2013 :  11:30:26 AM  Show Profile  Reply with Quote
Hi audio guru,
My best regards---I am looking to get more than 5 amps from the LM 338K or similar types reg.What if I place three or four in Paralell,in theory it is supposed to work ok? have anyone tried it successfully?.just checking--- will try it later,Unless you tell me otherwise. Best regards.
Hardeen
Go to Top of Page

Hardeen
New Member

2 Posts

Posted - May 14 2013 :  11:37:50 AM  Show Profile  Reply with Quote
Hi Audio guru,My best regards.
One question---Is it possible to Place more than one LM338 or similar types reg. in Parallel to increase the current output capacity.Guess this has been done or tried before. Best regards.
Hardeen
Go to Top of Page

audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - May 20 2013 :  8:11:25 PM  Show Profile  Reply with Quote
I guess you did not read the datasheet for the LM338.
The LM338 provides more than 5A (typically 8A) when it is cooled properly and the voltage from its input to its output is 10V or less.
The datasheet shows two circuits with three LM338 ICs with an obsolete opamp to provide 15A.
Also shown is a circuit with two LM338 ICs and an obsolete opamp to provide 10A.
Go to Top of Page
Page: of 2 Previous Topic Topic Next Topic  
Previous Page
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
Aaron's Homepage Forum © 1995-2020 AARONCAKE.NET Go To Top Of Page
This page was generated in 0.12 seconds. Snitz Forums 2000