How to simulate LDO regulator open loop gain and PM ?

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Re: LDO Gain

vbhupendra said:
how to simulate LDO regulator open loop gain & PM ?
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break the loop between resistors. connect this point and opamp's input by huge inductance for example 1G (to ensure operating point). pass ac source also by huge capacitor 1G
 

Re: LDO Gain

Hi,

Maybe the block below can help you to run LDO's AC analysis, which can bring you Gain & PM[/img][/list]

B.Regards.
 
Re: LDO Gain

Hi smartdream,
thanks, i am able to find gain & stability with this model.
but can u explain how this model works ?
 

LDO Gain

thanks a lot
 

Re: LDO Gain

Shouldn't the inputs of the error amp be connected in the reversed direction to ensure that the regulating loop is stable?
 

LDO Gain

Another way: the AC signal should be inserted into the input of negative input of AMP
 
Re: LDO Gain

jutek said:
break the loop between resistors. connect this point and opamp's input by huge inductance for example 1G (to ensure operating point). pass ac source also by huge capacitor 1G
Click to expand...

Hi,

I'm doing an LDO and I would like to know the gain. Could you tell me how you do it?

I'm doing dB20(VF("/vout")/VF("/vref")) but I'm not sure if it´s that. It's giving me a negative gain?

Could you help me?



thanks in advance
 

Re: LDO Gain

pseudockb said:
Shouldn't the inputs of the error amp be connected in the reversed direction to ensure that the regulating loop is stable?
Click to expand...

No, its correct, because the source follower does not invert the signal.

- - - Updated - - -

baniliu said:
Another way: the AC signal should be inserted into the input of negative input of AMP
Click to expand...

Not only "another way". It's the only correct way. The ac test signal must be injected into the lower node of the huge capacitor (which is presently grounded). That's the only purpose of the capacitor (see the figures attached to post#3).
 
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Re: LDO Gain

pseudockb said:
Shouldn't the inputs of the error amp be connected in the reversed direction to ensure that the regulating loop is stable?
Click to expand...

LvW said:
No, its correct, because the source follower does not invert the signal.
Click to expand...

In this case it's not a source follower; the pass transistor is inverting.

The feedBack connection is correct anyway.
 

Did you notice, that the schematics in post #3 and #8 have different amplifier gain sign? It's not clear which variant the comments are referring to.
 

FvM said:
It's not clear which variant the comments are referring to.
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True. I was referring to the last one (#8). Same as in this thread by the same author (seems like double posting).

For #3 I'd say it's not a source follower either, and the feedBack connection here is wrong.
 
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erikl said:
For #3 I'd say it's not a source follower either, and the feedBack connection here is wrong.
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Hey erik, can you tell me why I have seen a source follower in post#3? Because I can't. Thanks for correction.
 
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LvW said:
Hey erik, can you tell me why I have seen a source follower in post#3? Because I can't.
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Hi LvW, nor can I, that's what I told above. How should I know where you have seen a source follower in post#3? Must be a misunderstanding, I guess.
What, do you think, should be corrected?
 

erikl said:
Hi LvW, nor can I, that's what I told above. How should I know where you have seen a source follower in post#3? Must be a misunderstanding, I guess.
What, do you think, should be corrected?
Click to expand...

Erik, it was a joke. You have corrected my false reading of the scetch, didn't you?
 

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