LTspice simulation problem

meysaminter said:

UC3854 not UC3844!!!!!!!!!!!!!!!!!!!!!

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I am very sorry... I guess I need changing my glasses

they're usually not so good about building models of their competitors' parts

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They don't at all. You have to use standard SPICE models provided by part manufacturers. My impression of simulations with TINA specific switcher models is that they are too different from regular SPICE simulations to work for my purposes. But I didn't spent much time on it so far.

The other point is that simulation models of complex devices are limited in several regards and not necessarily represent the full part behaviour. At best, you get a brief information which aspects of device behaviour or modelled at all. It may be more reasonable to make your own functional model using behavioral modelling means.

UC3854 not UC3844!!!!!!!!!!!!!!!!!!!!!

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Too much!!!!!!!!! exclamation marks. The UC3844 model provided by Kerim is apparently such a kind of user model and can serve as a starting point for UC3854 modelling.

I changed my design to TL494 . I used it in Boost topology . I want to have 300V output . so I calculated the parameters . but when I simulated it in LTspice . the output voltage was aboat 190V !!! I changed many parameters but the output did't changed anymore. SO I don't now what to do!!! plz check my circuit and tell my what is wronge with it .

Among many other problems, wrong voltage divider values for TL494. The regulated steady-state output is around 100 V now.

Other points are unsuitable TL494 compensation network (should not use a parallel resistor),
missing VDD supply for IR2110.

I corrected the devider resistor and VDD for IR2110 . but still the output is 100V . When I change the parameters such as resistor devider, inductor and capasitor . the output don't change!!!!

You are right, I overlooked a major problem of your circuit. TL494 output duty cycle is limited to < 50 % when using a single output. Thus the boost converter can't exceed a step-up ratio of 1:2 in continuous mode. Both outputs of TL494 must be OR-ed.

FvM said:

You are right, I overlooked a major problem of your circuit. TL494 output duty cycle is limited to < 50 % when using a single output. Thus the boost converter can't exceed a step-up ratio of 1:2 in continuous mode. Both outputs of TL494 must be OR-ed.

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I OR-ed the outputs but nothing changed!!!!

You should look more thoroughly at the design signals (that's what simulation is good for). You'll notice that the output isn't switching at all - due to too high IR2110 VDD.

Your Vdd pin on the IR2110 does not have to have supply connected to it , only connect it to Vcc. Hence there was no propper output from the 2110 to drive the FET. The 100V output was due to the charge current into the inductor at startup causing the 100V output when it decayed.
Use the low side driver , not the high side driver in this sort of cct. Without a push pull drive from the chip , ther is no way to derive the high-side gat drive as there is no functioning
bootstrap cct.
Modified and attached. I've changed a few other values , but all else is the same.

Your Vdd pin on the IR2110 does not have to have supply connected to it , only connect it to Vcc.

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Maybe it's working with this behavioral IR2110 model. A real chip should not be operated without logic supply! But the supply voltage must be correct, e.g. 5V for a 5V input signal.