some question about using LT1316 as a flyback dcdc

I don't have time or expertise to analyze your netlist but as a regular user of LTspice let me suggest that you start a blank project. Click on the part icon and navigate to the LT1316 symbol and highlight it. Now, all you need to do is click on "Open this macromodel's test fixture". Bam. You should have a working circuit ready to run as is or modify as needed. I suggest that if you want to save a modified circuit, save it to a different location.

"Brett Holden" wrote in message news:Epkwl.17709$ snipped-for-privacy@bignews4.bellsouth.net...

I tried your circuit and made a few changes to make it work. It may not be ideal. I used a MOSFET from the LTspice library and I made the transformer with lower inductance. The 2N3904 seems to be a low power zener. I added another in series to boost the power supply voltage and thus give a better gate drive to the MOSFET. After 60 mSec the output had just about reached 5 VDC but it had not yet started regulating. I did not check the efficiency and you really need to wait until it reaches a steady state to do so. Probably 100 mSec, but it is a slow simulation as it is.

Good luck.

Paul

==================================================================================================== Version 4 SHEET 1 2012 852 WIRE -592 -160 -720 -160 WIRE 0 -160 -592 -160 WIRE 432 -160 0 -160 WIRE 672 -160 560 -160 WIRE 848 -160 736 -160 WIRE 944 -160 848 -160 WIRE 944 -128 944 -160 WIRE 848 -112 848 -160 WIRE 0 -80 0 -160 WIRE 432 -64 432 -80 WIRE 432 -64 304 -64 WIRE 304 -16 304 -64 WIRE 560 16 560 -80 WIRE 848 16 848 -48 WIRE 848 16 560 16 WIRE 944 16 944 -48 WIRE 944 16 848 16 WIRE -288 64 -432 64 WIRE -160 64 -288 64 WIRE 0 64 0 0 WIRE 0 64 -160 64 WIRE 144 64 0 64 WIRE 256 64 144 64 WIRE 688 80 576 80 WIRE 944 80 752 80 WIRE -432 176 -432 64 WIRE 144 192 144 64 WIRE 480 192 144 192 WIRE -352 224 -368 224 WIRE 0 256 0 64 WIRE -720 272 -720 -160 WIRE -592 272 -592 -160 WIRE 144 272 144 192 WIRE 304 272 304 80 WIRE 480 288 480 192 WIRE 688 288 480 288 WIRE 944 288 944 80 WIRE 944 288 752 288 WIRE -432 320 -432 272 WIRE -352 320 -352 224 WIRE -352 320 -432 320 WIRE -160 352 -160 64 WIRE 944 352 944 288 WIRE 944 352 688 352 WIRE -432 368 -432 320 WIRE 0 368 0 336 WIRE 64 368 0 368 WIRE 464 368 384 368 WIRE -352 416 -368 416 WIRE 944 416 944 352 WIRE -288 432 -288 64 WIRE 688 432 688 352 WIRE -432 464 -448 464 WIRE -160 464 -160 432 WIRE 64 464 -160 464 WIRE 432 464 384 464 WIRE -448 528 -448 464 WIRE -352 528 -352 416 WIRE -352 528 -448 528 WIRE -160 528 -160 464 WIRE 464 528 464 368 WIRE 688 528 688 512 WIRE 688 528 464 528 WIRE 688 560 688 528 WIRE 144 608 144 560 WIRE 0 720 0 368 WIRE 432 720 432 464 WIRE 432 720 0 720 WIRE -720 736 -720 352 WIRE -592 736 -592 336 WIRE -592 736 -720 736 WIRE -448 736 -448 528 WIRE -448 736 -592 736 WIRE -288 736 -288 496 WIRE -288 736 -448 736 WIRE -160 736 -160 608 WIRE -160 736 -288 736 WIRE 144 736 144 688 WIRE 144 736 -160 736 WIRE 304 736 304 560 WIRE 304 736 144 736 WIRE 576 736 576 160 WIRE 576 736 304 736 WIRE 688 736 688 640 WIRE 688 736 576 736 WIRE 944 736 944 480 WIRE 944 736 688 736 WIRE -720 784 -720 736 FLAG -720 784 0 FLAG 560 16 0 SYMBOL ind2 416 -176 R0 SYMATTR InstName L1 SYMATTR Value 200µ SYMATTR Type ind SYMBOL ind2 576 -64 R180 WINDOW 0 36 80 Left 0 WINDOW 3 12 36 Left 0 SYMATTR InstName L2 SYMATTR Value 2µ SYMATTR Type ind SYMBOL schottky 672 -144 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 928 -144 R0 SYMATTR InstName R1 SYMATTR Value 300 SYMBOL cap 832 -112 R0 SYMATTR InstName C1 SYMATTR Value 200µ SYMBOL PowerProducts\\\\LT1316 224 416 R0 SYMATTR InstName U1 SYMBOL ind2 592 176 R180 WINDOW 0 36 80 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName L3 SYMATTR Value 2µ SYMATTR Type ind SYMBOL diode 688 96 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode 752 272 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL cap 928 416 R0 SYMATTR InstName C3 SYMATTR Value 1µ SYMBOL res 672 416 R0 SYMATTR InstName R2 SYMATTR Value 50K SYMBOL res 672 544 R0 SYMATTR InstName R3 SYMATTR Value 12.7K SYMBOL res 128 592 R0 SYMATTR InstName R4 SYMATTR Value 69.8K SYMBOL res -16 240 R0 SYMATTR InstName R100 SYMATTR Value 2000k SYMBOL res -16 -96 R0 SYMATTR InstName R6 SYMATTR Value 220K SYMBOL res -176 336 R0 SYMATTR InstName R5 SYMATTR Value 1300k SYMBOL res -176 512 R0 SYMATTR InstName R7 SYMATTR Value 604k SYMBOL cap -304 432 R0 SYMATTR InstName C2 SYMATTR Value 1µ SYMATTR SpiceLine V=10 Irms=10.541 Rser=0.004 Lser=0 mfg="KEMET" pn="C0603C105K8PAC" type="X5R" SYMBOL cap -608 272 R0 SYMATTR InstName C4 SYMATTR Value 0.022µ SYMBOL voltage -720 256 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 40 SYMBOL npn -368 464 R180 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL nmos 256 -16 R0 SYMATTR InstName M2 SYMATTR Value SUD40N10-25 SYMBOL npn -368 272 R180 SYMATTR InstName Q2 SYMATTR Value 2N3904 TEXT 408 -200 Left 0 !K1 L1 L2 L3 1 TEXT -752 808 Left 0 !.tran 0 60m 1m startup

Is ther no way to set an intial condtion on the output cap to speed the sim?

Probably a 5VDC source through a diode would preset it to 4.3 VDC and that might speed things up. Good idea! There may be a way to preset conditions directly in SPICE, but I don't know how,

Paul

.IC -- Set Initial Conditions

The .ic directive allows initial conditions for transient analysis to be specified. Node voltages and inductor currents may be specified. A DC solution is performed using the initial conditions as constraints. Note that although inductors are normally treated as short circuits in the DC solution in other SPICE programs, if an initial current is specified, they are treated as infinite-impedance current sources in LTspice.

Syntax: .ic [V()=] [I()=]

Example: .ic V(in)=2 V(out)=5 V(vc)=1.8 I(L1)=300m

ll

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=AD=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D

Thank you paul. But i have another question that is:The mosfet's M2 action. I think the mosfet make the voltage of Sw low than 30V(Sw -0.3 - 30). And te datasheet said the efficiency of this circuit is 75%(udner input 25V to 50V). So the question is that if the input voltage is more than 40V the efficiency must be lower than 75%. why?

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I don't know why the efficiency should be lower at a higher voltage. Usually the duty cycle is lower and losses from RdsOn are less significant, so I would expect the reverse to be true. But I found that the circuit as shown in the datasheet regulates at about 6.5 VDC, and the rough efficiency calculation I did looked more like 50%, which is very poor. Even 75% is not impressive. I think there are some problems with the circuit as drawn, and perhaps you should try the flyback circuit in the LTC folder as a starting point.

Also, I tried setting initial conditions and had problems with some values for the output voltage, but it did work when I used lower values and the simulation was faster.

Paul