LM338: Pspice simulation

Nurul Hamzah

Part Number: LM338
Other Parts Discussed in Thread: LM317,

Hello, I am trying to run this circuit using Pspice, however, I didnt get the desired output current which is 1A. Can you help me? Thank you in advance

over 1 year ago

0 Stephen Ziel over 1 year ago

TI__Mastermind 35485 points

Hi Nurul,

It looks like you are trying to simulate this circuit in the datasheet. The output of this circuit is between the LM338 and LM317, labeled Iout in the image below. You should not expect 1A flowing through R3. R3 = 120 ohms, and the internal reference is 1.24V. So you should expect about 10mA across R3. Therefore the LM317 sinks a constant 10mA despite the voltage on Iout node, which keeps the LM338 regulating properly as the LM338 has a minimum load current requirement of 10mA (worst case).

Thanks,

Stephen

0 Nurul Hamzah over 1 year ago in reply to Stephen Ziel

Prodigy 10 points

hello Stephen, thank you for answering my question. I had tried simulating the same circuit with the load (a 12V Li-ion battery) and I construted it using resistors and capacitor. but however I still didnt get 1A as the output current. can you perhaps show me which part of the circuit did I do wrong? thank you in advance!

0 Stephen Ziel over 1 year ago in reply to Nurul Hamzah

TI__Mastermind 35485 points

Hi Nurul,

You'll want a DC source for V1, not an AC source. If you set your DC source to something like 10V, then you'll need to configure R5 to be no greater than (Vin - 3) / 1A = (10V - 3V) / 1A = 7 ohms in the simulation. You shouldn't need the R6 resistor, you can delete that.

Thanks,

Stephen

0 Nurul Hamzah over 1 year ago in reply to Stephen Ziel

Prodigy 10 points

did i do it correctly? but i still didnt get 1A

0 Stephen Ziel over 1 year ago in reply to Nurul Hamzah

TI__Mastermind 35485 points

Try this:

Thanks,

Stephen

0 Nurul Hamzah over 1 year ago in reply to Stephen Ziel

Prodigy 10 points

hello, i have change the value of resistor to 7ohms but i still cant get the desired result. what do you suggest?

the load is supposed to be a 12v battery as i was trying to charge the battery.

0 Stephen Ziel over 1 year ago in reply to Nurul Hamzah

TI__Mastermind 35485 points

Set R2 = 1.05 ohms and see if that works.

Thanks,

Stephen

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LM338: Pspice simulation