DC-DC buck converter large signal modeling in spice

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Hello

I have studied about spice modeling, especially buck converter.

?? ??027.jpg

To realize this schematic, i write netlist like this


VG VIN GND VIN_para
RIN VIN V0 RL_para
V_DC_IN V0 V1 DC 0
F1 V1 GND V_DC_OUT 'N(V(VD,0))'
E1 V2 GND VIN GND 'N(V(VD,0))'
V_DC_OUT V2 V3 DC 0
L0 V3 VOUT 100uH
CL VOUT GND 10uF
RL VOUT GND 100

VD VD GND DC 'VOUT_PARA/VIN_PARA' AC 1

.param N(x)='x'
.param VIN_PARA=12
.param VOUT_PARA=5
.param RL_para=0.1

.tran 1u 10m
.probe V(*) I(V*) I(ROUT)
.AC DEC 100 1m 1G
.probe VDB(VOUT) VP(VOUT) VDB(VD)
.PRINT GAIN=par('V(VOUT)/V(VD)')
.end

in transient simulation, result is correct. but ac simulation, gain and phase is so strange.

in this text book, ac simulation is like this.

?? ??028.jpg

bu t my result is not corresponding. I appreciate that there is anyone who can explain about this.

thanks
 

I neither understand the schematic nor the meaning of the term "large signal modeling" related to it.

In my view, you can perform two kinds of simulations of a switched mode circuit:
- simulation of the real switching circuit, obviously involving a PWM modulator
- simulation of a continuous time equivalent circuit

AC analysis can be only performed on the latter, but you have to derive the equivalent circuit first. A particular problem is raised by the parameter variation when changing between CCM and DCM.
 

Try to set in a .AC directive frequency range 10 Hz - 100 kHz (as in the book) and 101 (not 100) points.
 

Extending to What Fvm said, if you can replace the transformer by a simple GAIN block (with gain equal to step up or step down ratio), i expect to see expected response. Also I would place VAC in place of VDC in that case.
 

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