Pure sin wave inverter

[Tahmid]

Add a large enough deadtime by adding a large resistance between pins 5 and 7. The maximum value allowable is 500Ω. So use 470Ω.

If that is insufficient, you may limit duty cycle by using feedback from the output AC signal.

 

[--BawA--]

hi tahmid ,
i m still facing one problem, when i set the output voltage of the dc bus at 260 volts and connect two 100w +100w bulb ,the output voltage remains constant, but if i increase the output voltage to 311volts using trimpot with only one bulb 100w connected , and then as i connect the second 100w bulb my output voltage goes to 269 volts ,,,so what can i do so that my output voltage should constant 311volts , with 200watt loads ,,
feedback is working , i hve also used 3mh inductor at the filter stage,,,so where should i change, should i increase the no. of secondary turns of the transformer?

 

[Tahmid]

When you increase output voltage to 311V and use 200W load, do the MOSFETs get very hot? Hotter than when set using 269V?

Can you state your transformer turns - primary and secondary?

 

[--BawA--]

MOSFET get hot in both the case ,,, but i cant say exactly that in which case it gets too hot
, primary turns- 2
secondary turns -65
core etd44
frequency 50khz
one thing i hve noticed that the heat sink connected to my one side mosfet bank get slightly more hot than the heat sink that is conncted to second mosfet bank..

 

[Tahmid]

How many MOSFETs do you have in parallel in each leg?

Did you use any driver after the SG3525?

Measure the voltages at SG3525 pins 11 and 14 in all cases - when voltage is 260V with 200W load, when voltage is 311V with 100W load and when voltage is 269V with 200W load. Post your results.

 

[--BawA--]

hi tahmid, till now, i didn't use any driver after sg3525 , i used it directly, one thing i hve noticed that at 200 watt loads my battery pottential goes to 10.5 volts, .

- - - Updated - - -

i think that i should use tc427 after sg3525 , perhaps my mosfet was not getting fully ON,, i found tc427 yesterday very hardly, w0hat do u think , will it resolve the problem?

 

[Tahmid]

Since your transformer is for 12V to 390V, at 10.5V input the output shouldn't drop to 269V. (10.5/12 * 390V) = 341.25V

The lack of a driver after the SG3525 could be a problem. So TC427 might resolve the issue.

 

[--BawA--]

hi tahmid
i have read your blog, i have one confusion , i want my frequency to be 50khz, so i have set the frequency of sg3525 to 50khz, should i adjust the frequency to 100khz , for obtaining 50khz ,,,i m confused , please explain??

 

[Tahmid]

The SG3525 oscillator should be set for 100kHz and the output frequency you will observe at the output pins will be 50kHz.

Hope this helps.
Tahmid.

 

[--BawA--]

tahmid, what is the reason behind this? why we obtain a frequency of 50khz ,if we set the frequency to 100khz?

 

[Tahmid]

tahmid, what is the reason behind this? why we obtain a frequency of 50khz ,if we set the frequency to 100khz?

There is a flip-flop before the driver stage, due to which your output signals will have frequencies half that of the oscillator frequency that is calculated using the formula.

Hope this helps.
Tahmid.

 

[picgak]

hi tahmid, till now, i didn't use any driver after sg3525 , i used it directly, one thing i hve noticed that at 200 watt loads my battery pottential goes to 10.5 volts, .

Mostly the overheating of mosfets are due to the voltage drop as indicated , because at this time the gate voltage may not be sufficient.

 

[kabeer02]

Your battery should'nt go to 10volt even if you load up to 350watts,that means you need to check your batt also.

 

[--BawA--]

hi tahmid,,
i hve used tc427 after sg3525 ,,,and also i hve set my oscillator frequency to 100khz so that switching frequency can be 50khz,,,now the problem is,,,my output voltage does not go beyond 297volts at 100 watt load ,,,and when i connect a 200watt bulb the output goes to 230volts,,,,where is the problem??? one thing that i hve noticed is that my left side mosfet bank get hot quickly in comparison to right side mosfet bank,,,,i m very confused right now,please suggest me a way...

 

[picgak]

hi tahmid,,
i hve used tc427 after sg3525 ,,,and also i hve set my oscillator frequency to 100khz so that switching frequency can be 50khz,,,now the problem is,,,my output voltage does not go beyond 297volts at 100 watt load ,,,and when i connect a 200watt bulb the output goes to 230volts,,,,where is the problem???,,,,i m very confused right now,please suggest me a way...

The voltage problem is in your feed back circuit, if you can post the feed back circuit we can try to solve it

 

[kabeer02]

post your complete diagram if possible we will see where the problem is.

 

[--BawA--]

I hve successfully designed my full bridge circuit which was controlled by microcontroller, I was getting 325v output at my h bridge..after attaching a low pass lc filter , my hbridge mosfets blown out .I have used electlolytic capacitor in my filter design.. what was the reason behind that ??
Are electolytic capacitor not used in lc filters?? Plz reply

 

[kabeer02]

we can know what is going on without your circuit diagram.

 

[picgak]

I hve successfully designed my full bridge circuit which was controlled by microcontroller, I was getting 325v output at my h bridge..after attaching a low pass lc filter , my hbridge mosfets blown out .I have used electlolytic capacitor in my filter design.. what was the reason behind that ??
Are electolytic capacitor not used in lc filters?? Plz reply

Hi Bawa,
Kabeer is right if you really want answer to the above question please attach at least the portion of the circuit you are talking about.

 

[Tahmid]

I hve successfully designed my full bridge circuit which was controlled by microcontroller, I was getting 325v output at my h bridge..after attaching a low pass lc filter , my hbridge mosfets blown out .I have used electlolytic capacitor in my filter design.. what was the reason behind that ??
Are electolytic capacitor not used in lc filters?? Plz reply

Did you use polarized electrolytic capacitors? You can't do that unless you've connected two back-to-back to create a non-polar capacitance. The output is AC. And the use of a polarized capacitor will damage the capacitor and other parts of the circuit too if the capacitor is shorted.

For better answers and suggestions, you will need to upload the schematic of the circuit you're using.

Hope this helps.
Tahmid.