Obtaining Bode plots for SMPS feedback loop

eem2am · 22nd October 2011, 02:53 PM

Hello,

Is there any company, anywhere in the world, that can provide us with Bode Plots for the SMPS Feedback loop if we send them our SMPS schematic and the specification to which the SMPS is intended.?

darkfenriz · 22nd October 2011, 03:09 PM

I am not a company, but can do it for you.

jcx · 22nd October 2011, 04:20 PM

Linear Technology (free) Ltspice and very long sim times can be used, with some difficulty since they dropped their BodeCad sw

Ridley Engineering does it in hardware - I haven't used it but the site looks like it has lots of solid info on sw mode

eem2am · 22nd October 2011, 07:08 PM

Hi,

As far as i see, LTSpice doesnt have voltage mode full-bridge pwm controllers, so i wouldnt be able to put many of our schematics in there.

I have previously used LTSpice to get individual points on the Gain and phase plots......but it would be very time consuming to get enough points for a whole plot.

I have the book by Basso that gives transfer functions for certain standard TL431/Opto feedback circuits, but many of our schematics dont use those standard types, because of eg high, split output voltages such as +/-50V.

darkfenriz · 22nd October 2011, 08:22 PM

Every PWM modulator has its well defined gain.
It is easy to simulate that as a linear gain and perform an AC sweep.

jcx · 22nd October 2011, 09:00 PM

fine for well defined operating conditions - not so much for transition to discontinuous mode, inductor saturation, hard nonlinearities that may give sub-harmonic or other decidedly nonlinear behaviors

but by all means if your circuit can be modeled simiply with state space averaging do that 1st

Ltspice does use encrypted models of their own Sw Reg parts but if you have a Spice model for your part it can be ran in Ltspice

I have used VBA to extract numbers from a Ltspice log file - use the .meas commands in Ltspice

ran stepped sims overnight to obtain points for a graph

22nd October 2011, 02:53 PM	#1
eem2am diyAudio Member Join Date: Jun 2011	Obtaining Bode plots for SMPS feedback loop Hello, Is there any company, anywhere in the world, that can provide us with Bode Plots for the SMPS Feedback loop if we send them our SMPS schematic and the specification to which the SMPS is intended.?

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22nd October 2011, 03:09 PM	#2
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	I am not a company, but can do it for you.

22nd October 2011, 04:20 PM	#3
jcx diyAudio Member Join Date: Feb 2003 Location: ..	Linear Technology (free) Ltspice and very long sim times can be used, with some difficulty since they dropped their BodeCad sw Ridley Engineering does it in hardware - I haven't used it but the site looks like it has lots of solid info on sw mode

22nd October 2011, 07:08 PM	#4
eem2am diyAudio Member Join Date: Jun 2011	Hi, As far as i see, LTSpice doesnt have voltage mode full-bridge pwm controllers, so i wouldnt be able to put many of our schematics in there. I have previously used LTSpice to get individual points on the Gain and phase plots......but it would be very time consuming to get enough points for a whole plot. I have the book by Basso that gives transfer functions for certain standard TL431/Opto feedback circuits, but many of our schematics dont use those standard types, because of eg high, split output voltages such as +/-50V.

22nd October 2011, 08:22 PM	#5
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Every PWM modulator has its well defined gain. It is easy to simulate that as a linear gain and perform an AC sweep.

22nd October 2011, 09:00 PM	#6
jcx diyAudio Member Join Date: Feb 2003 Location: ..	fine for well defined operating conditions - not so much for transition to discontinuous mode, inductor saturation, hard nonlinearities that may give sub-harmonic or other decidedly nonlinear behaviors but by all means if your circuit can be modeled simiply with state space averaging do that 1st Ltspice does use encrypted models of their own Sw Reg parts but if you have a Spice model for your part it can be ran in Ltspice I have used VBA to extract numbers from a Ltspice log file - use the .meas commands in Ltspice ran stepped sims overnight to obtain points for a graph

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