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--- In LTspice@..., "imbvlad" <imbvlad@> wrote:

Hello

You may want to try the other Yahoo group, "switchmode", they may have the answers you're looking for.


Good luck,
Vlad

Hi,
i was thinking that the main component what i have used is of LT and so this group should be aiding me.

Thanks
Yoga

--- In LTspice@..., "yogasmitha" <amba_200@> wrote:

Also, I have saved the .asc file in database for your reference which i have been using/trying to modify :flyback_nom.asc

--- In LTspice@..., "yogasmitha" <amba_200@> wrote:

--- In LTspice@..., "imbvlad" <imbvlad@> wrote:

Hello

You may want to try the other Yahoo group, "switchmode", they may have the answers you're looking for.


Good luck,
Vlad

Hi,
i was thinking that the main component what i have used is of LT and so this group should be aiding me.

Thanks
Yoga

Yoga,

You are missing a ground on the bottom half of your circuit. Here are some other comments:
1. You could 'clean up' your circuit by combining all the parallel caps and series resistors.
2. You don't need any caps in parallel with the DC voltage sources that have zero resistance.
3. Your current pulses aren't going to work right, because the sum of the various times exceeds the period.

Rick

--- In LTspice@..., "yogasmitha" <amba_200@> wrote:

Hello Rick,
Thanks, But i have connected the ground on the R285 to R295 resistors. Which is ground. Do you think there has to be some big resistor at the return path? say 100K since the input and the output side will have a common grounds and as i said it will short the return path?

Do you have any other source or database which can give me the esr of the caps i am using.
SInce i know these will contribute a lot to the instability.

another thing i want to know is " i have used the inductor as a flyback transf and want to know if the series resistance is calculated by the ltspice tool on its own"
i have given the direct values of 0.045Ohm what is given in the datasheet. What actually is seen by the coil is based on the connectivity. i.e parallel or series etc.., Will lt tool calculate on own since the coil craft vendor told me the LT tool will do. I just wanted to clarify once with you.

What are the other values/components which affect the stability of the flyback?
Should i try to do something with the comp pin(values) of the LT1241 device?

Ple Help.
Thanks,
Yoga

Yoga,

You're right, you do have a connection there. When I looked at your circuit before, I saw a very large voltage between ground and the common bus on the bottom half of the circuit. This caused by the inductance between ground and the common bus and the very larges start up currents in the circuit. I removed UIC from the .TRAN command and the startup currents were greatly reduced. (You could do this other ways, but this was easy to do.) You should revisit your filtering scheme.

After I removed UIC, the circuit seemed to behave OK. Specifically, what do you think is wrong?

LTspice contains a library of caps with their ESRs. In addition, part manufactures specify ESR.

LTspice does not compute the inductor series resistance but it defaults to .001 ohms for inductors that are not mutually coupled to others. LTspice also has a library of inductors, and vendors specify performance. The model LTspice uses for an inductor is given in the help file.

Rick

Hi,
I will try by removing uic from .tran command. Coming back to the initial problem i started with,
When the flyback is working and is stable,the output of the flyback of pos5v is used by another circuit (LTC1778) which converts pos5v to pos 3.3V.
When a load of 8-9W of load from the 2A on the 3.3V is REMOVED, the pos5V sees a very noticeable dip/raise in the voltage which results in reset of CPU.

This is what i am thinking the flyback is not stable and so it has got something to do with the esr of caps, and the leakage inductance and the return ground etc..,
i cannot think of anything else what might be the issue.
However the lab results are not as bad as the simulation results but it still resets the cpu.

Pl Help
Thanks,
Yoga

--- In LTspice@..., "sawreyrw" <sawreyrw@> wrote:

--- In LTspice@..., "yogasmitha" <amba_200@> wrote:

Hello Rick,
Thanks, But i have connected the ground on the R285 to R295 resistors. Which is ground. Do you think there has to be some big resistor at the return path? say 100K since the input and the output side will have a common grounds and as i said it will short the return path?

Do you have any other source or database which can give me the esr of the caps i am using.
SInce i know these will contribute a lot to the instability.

another thing i want to know is " i have used the inductor as a flyback transf and want to know if the series resistance is calculated by the ltspice tool on its own"
i have given the direct values of 0.045Ohm what is given in the datasheet. What actually is seen by the coil is based on the connectivity. i.e parallel or series etc.., Will lt tool calculate on own since the coil craft vendor told me the LT tool will do. I just wanted to clarify once with you.

What are the other values/components which affect the stability of the flyback?
Should i try to do something with the comp pin(values) of the LT1241 device?

Ple Help.
Thanks,
Yoga

Yoga,

You're right, you do have a connection there. When I looked at your circuit before, I saw a very large voltage between ground and the common bus on the bottom half of the circuit. This caused by the inductance between ground and the common bus and the very larges start up currents in the circuit. I removed UIC from the .TRAN command and the startup currents were greatly reduced. (You could do this other ways, but this was easy to do.) You should revisit your filtering scheme.

After I removed UIC, the circuit seemed to behave OK. Specifically, what do you think is wrong?

LTspice contains a library of caps with their ESRs. In addition, part manufactures specify ESR.

LTspice does not compute the inductor series resistance but it defaults to .001 ohms for inductors that are not mutually coupled to others. LTspice also has a library of inductors, and vendors specify performance. The model LTspice uses for an inductor is given in the help file.

Rick