Home Community

LM338 Power Suply Current Regulator

 Pages: [1] 2 3 ... 6
 Author Topic: LM338 Power Suply Current Regulator  (Read 10283 times)
Fight
Newbie

Posts: 44

 « on: May 26, 2010, 12:44:14 PM »

Features:
Guaranteed 7A peak output current
Guaranteed 5A output current

But problem is that in Electrical Characteristics:
Vin-Vout = 30V Than max current 1A
what is meaning that
lets Vin = 38V  and Vout = 8V
38-8 = 30

and Vin-Vout = 10V or less than 5A can handle
mean
38-28 = 10
mean 8 to 28V 1A handle
and 28 to above 5A handle

Attatch Diagram

2.    in Application Hints diagram all diagram is designed that can handle 5A

Attatch Diagram
 Logged

hotwaterwizard
Moderator
Electronics God

Gender:
Posts: 2231

Service Tech

 « Reply #1 on: May 27, 2010, 11:15:18 PM »

Exactly what are you wanting to do here?

You Must Heatsink the components for 5 amps each if not they will only handle 1 amp each.
There is another way to make a high current power supply.
 Logged

John DeRosa (Hotwaterwizard)

When in Doubt, Try it out!!

hotwaterwizard
Moderator
Electronics God

Gender:
Posts: 2231

Service Tech

 « Reply #2 on: May 27, 2010, 11:36:51 PM »

 Logged

John DeRosa (Hotwaterwizard)

When in Doubt, Try it out!!

Hero999
Global Moderator
Electronics God

Posts: 2471

 « Reply #3 on: May 28, 2010, 04:02:26 AM »

Exactly what are you wanting to do here?

You Must Heatsink the components for 5 amps each if not they will only handle 1 amp each.
There is another way to make a high current power supply.

That circuit will have very poor regulation because the base-emitter saturation voltage of the 2N3055 will vary depending on the current drawn and the 0.47R resistors will have a significant voltage accross them.

Suppose the current draw is 0A and you set the voltage to 12V.

Then you increase the current to 5A.

@0A the VBE of the transistors will be near 0.6V.

Each transistor will have 5/6 = 833mA through it, the same for the emitter resistor.

The voltage will drop by the 0.47R resistor will be 5/6
 Logged

I also post at:
http://www.silicontronics.com

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question: if I know the answer, I'll be happy to help.

Fight
Newbie

Posts: 44

 « Reply #4 on: May 28, 2010, 05:50:14 AM »

Quote
The LM338 will only be able to output 5A if the difference between the input and output voltage is under 10V and a good heat sink is used (1
 Logged

Hero999
Global Moderator
Electronics God

Posts: 2471

 « Reply #5 on: May 28, 2010, 08:02:56 AM »

Quote
The LM338 will only be able to output 5A if the difference between the input and output voltage is under 10V and a good heat sink is used (1
 Logged

I also post at:
http://www.silicontronics.com

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question: if I know the answer, I'll be happy to help.

Fight
Newbie

Posts: 44

 « Reply #6 on: May 28, 2010, 12:11:12 PM »

Very Very Thanks Hero
 Logged

Fight
Newbie

Posts: 44

 « Reply #7 on: May 28, 2010, 12:16:47 PM »

 Logged

Fight
Newbie

Posts: 44

 « Reply #8 on: June 05, 2010, 12:20:06 PM »

Attatch diagram
what is the role of emittr resistance 0.1 ohm
why using this resistor
 Logged

Hero999
Global Moderator
Electronics God

Posts: 2471

 « Reply #9 on: June 05, 2010, 05:11:19 PM »

They help to ensure the current is shared equally between the transistors. The value isn't critical, I chose 0.1R because I originally designed it for high currents, for 5A you can use 1R which will be easier to get hold of.
 Logged

I also post at:
http://www.silicontronics.com

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question: if I know the answer, I'll be happy to help.

Fight
Newbie

Posts: 44

 « Reply #10 on: June 06, 2010, 01:44:02 AM »

if i change the value of 1R instead of 0.1R than what change in circuit current
the resistor wattage
the voltage across R = ?
the current across R = ?
 Logged

Hero999
Global Moderator
Electronics God

Posts: 2471

 « Reply #11 on: June 06, 2010, 02:54:23 AM »

Changing the value will not change the current, the circuit does not provide current regulation, it's just that if the voltage drop across the resistors is very low, the current sharing won't be very good.
 Logged

I also post at:
http://www.silicontronics.com

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question: if I know the answer, I'll be happy to help.

Fight
Newbie

Posts: 44

 « Reply #12 on: June 06, 2010, 04:50:54 AM »

Quote
it's just that if the voltage drop across the resistors is very low, the current sharing won't be very good.

if 10R resistor use than
 Logged

Fight
Newbie

Posts: 44

 « Reply #13 on: June 06, 2010, 04:57:42 AM »

what is the efficiency of these circuit
if this method using with lm317 and lm338 than thses ic better current and voltage or not
 Logged

 Pages: [1] 2 3 ... 6
 Jump to: Please select a destination: ----------------------------- Electronics Forums ----------------------------- => Projects Q/A => Datasheet/Parts requests => Electronic Projects Design/Ideas => Power Electronics => Service Manuals => Theory articles => Electronics chit chat => Microelectronics ----------------------------- Related to Electronics ----------------------------- => Spice Simulation - PCB design => Inventive/New Ideas => Mechanical constructions/Hardware => Sell/Buy electronics - Job offer/requests => Components trade => High Voltage Stuff => Electronic Gadgets ----------------------------- General ----------------------------- => Announcements => Feedback/Comments => General