some question about using LT1316 as a flyback dcdc

[mayichao]

http://mail.ustc.edu.cn/~ycma/1316flyback.asc
this is the asc file.
I just draw the schematic as same as Lt1316 datasheet,but when i run
it there is some mistake.
first the nSHDN is always 0.
So LT1316 is not working.
the 2n3904's work as a diode?

thanks.



ps :zvn4424 spice model
******************************************************************
SPICE PARAMETERS
*ZVN4424 MODEL LAST REVISION 1/94
*
..SUBCKT ZVN4424 30 40 50
* NODES: DRAIN GATE SOURCE
M1 30 20 50 50 MOD1 L=1 W=1
RG 40 20 200
RL 30 50 240E6
D1 50 30 DIODE1
..MODEL MOD1 NMOS VT0=1.25 RS=2.34 RD=1.634 IS=1E-15 KP=5.319
+CGS0=101P CGD0=4P CBD=66.2P PB=1
..MODEL DIODE1 D IS=5.516E-13 RS=0.2084 N=1.0078
..ENDS ZVN4424

 

[Brett Holden]

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.

 

[Paul E. Schoen]

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.

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

 

[Hammy]

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

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

 

[Paul E. Schoen]

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

 

[Nobody]

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,

..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(<n1>)=<voltage>] [I(<inductor>)=<current>]

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

 

[mayichao]

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?

 

[Paul E. Schoen]

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.

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?

=========================================================================

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