how to decide the triange wave and input signal amplitude.??

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Disabled Account
Joined 2004
titanchen68 said:
Thanks a lot ....
So , if the clamp circuit put in the error-amp will get better than clamp in the pre-amp , right ???
You said it will not getting an accurate clamp by using zener, but it seems to be a good ideal for now.

I still do not understand the different between the clamping around the error-amp and in the pre-amp.
Isn't it to clamp the input signal not exceed the triangle wave amplitued ??

what do you feel that i clamp the input signal amplitude to be 75% of triangle wave amplitude ??
Is it too lower or higher???

That is becoming my guess however I am now seeing problems elsewhere. For the moment it seems to be the easiest solution. For now, yes back to back zeners seem to be an easy fix but you should check the manufacturers data. I'm not certain but I think you will find that higher power devices, within reason, have better characteristics. They will have higher capacitance though.

If you clamp around the error amplifier then you gaurantee the level at which you clamp. If you clamp the input signal you have to take into account the effects of both the input signal and that from the feedback signal. I'm not saying it won't work but the behaviour is likely to be more complex.

As for the level you might choose then, assuming there is nothing else upsetting things then, unless you can calculate a true figure for deadtime in your circuit, it's not unreasonable to use the circuit itself to find out what the level should be.

DNA
 
I have bought the 3v zener diode use to clamp in error-amp.
And I'll try it later.

Yesterday , i want test the highest output amplitude.
So , i use function generator be the input signal.
I am testing in No Load. ( It seems not a good ideal )
When the inpug signal too big to clip the output signal that after LC filter.
The outuput mosfet burned out immediatly.
Is that right ???

Because i want to test the relationship between input signal and output waveform.
do i have anyother way to test ???
 
Disabled Account
Joined 2004
titanchen68 said:
I have bought the 3v zener diode use to clamp in error-amp.
And I'll try it later.

Yesterday , i want test the highest output amplitude.
So , i use function generator be the input signal.
I am testing in No Load. ( It seems not a good ideal )
When the inpug signal too big to clip the output signal that after LC filter.
The outuput mosfet burned out immediatly.
Is that right ???

Because i want to test the relationship between input signal and output waveform.
do i have anyother way to test ???


titanchen68 said:


Yes , i am .
Is that strange ???
Because I don't why , i only think is ShotThrought !
But i remember the Ir2110 has internal Dead time , i think it will not happen.

Sorry, I'm not sure I can help here.

Although some IRF drivers do include deadtime the IR2110 does not so you have to generate it in some other way. It looks like your gate diode/resistor combination is being used to achieve this and if things are not going wrong during normal operation the method may be working.

I'm sure someone else has mebtioned the bootstrap supply for the IC not being recharged during clipping. Your circuit shows a 40V supply but I assume that is a mistype. Maximum current drain is specified as 250uA so a 15V supply would drop to undervoltage lockout in about 18mS, which is quite a low frequency.

Even so you might expect the undervoltage lockout to prevent nasty things from happening although the data sheet makes no mention of drive or levels under these conditions.

Sorry, at the moment nothing else comes to mind...

DNA
 
Hi Titan,

If the bootstrap is not sufficient to provide enough voltage to charge the gates of mosfet, then this could happen during clipping...yes i had experienced this...you can also increase the boot Cap value upto 50MFD to maintain sufficient charge in case of hard clipping....

Second best way is to use an isolated floating supply reference to the source of High side Mosfet and then feed the VB from it, I have used this technique to enable the gate driver to give as much as charge to the gates of mosfets with Qg>300nC...No destruction at hard clipping with this technique....

K a n w a r
 
Thanks for replying....

I will try to increase the bootstrape cap to 50uF.
That sounds a good ideal , But in this technique , don't i still use large bootstrape cap to maintain the sufficient charging ???

After this project , i get a summy for voltage disigned.
The +/-RAIL voltage effected by :
1. maximum output power
2. triangle amplitude and output amplitude of error-amp

This project i want to create a 400Wrms in 4ohm
(didn't consider about voltage drop in mosfet)
so , i use a +/-55V rail voltage , 56*56/4/2 = 392Wrms
But i clamp my error-amp to 3.6v , the triangle wave amplitude is 4v.
In maximum , i only get 90% of maximum ouput voltage.
And only get 81% of maximum output power.
Only 392*0.81 = 317Wrms.

Did i get any wrong ???
 
Workhorse said:
Have you used the 50MFD cap....whats the result after that?

K a n w a r

I add a DC protect , and used the 50uF bootstrape cap.
When the output wave amplitude near +/-RAIL, after about 1sec , the DC protect working.
But the output mosfet didn't burned.
I think if didn't have dc proctect , the mosfet will burned,too.
But i don't know what will happen if i didn't add the dc protec circuit.
 
Disabled Account
Joined 2004
Just a thought......

With such a fast comparator and if your error amplifier pole capacitor is too small it may be possible that as your output approaches the rail you end up with multiple switching transitions somewhere in the circuit.

These might be too fast for the IR2110/gate circuit to handle with the result that you end up with your mosfets in the linear region and that causes them to go bang.....

DNA
 
Genomerics said:
Just a thought......

With such a fast comparator and if your error amplifier pole capacitor is too small it may be possible that as your output approaches the rail you end up with multiple switching transitions somewhere in the circuit.

These might be too fast for the IR2110/gate circuit to handle with the result that you end up with your mosfets in the linear region and that causes them to go bang.....

DNA


So , if the cap in the error amplifier is big enought, It will not happen???
I will try maybe 1n to 4n7 cap to test.
 
Disabled Account
Joined 2004
Hang On If your previously posted circuit diagram is close to what you have at the moment I'll throw it into LTspice and see if something good comes out.

It won't be precisely precise but I'll have a fiddle and post something on my website.

I'll let you know here when it's there.......

Cheers

DNA
 
Genomerics said:
Hang On If your previously posted circuit diagram is close to what you have at the moment I'll throw it into LTspice and see if something good comes out.

It won't be precisely precise but I'll have a fiddle and post something on my website.

I'll let you know here when it's there.......

Cheers

DNA


This is my newest circuit , i change some compoment value.
And change level shift prototype.
 

Attachments

  • my_class-d.pdf
    22.7 KB · Views: 128
Today , i test the amp . It has a big problem.
I use +/- 55v , i assume the output amplitude will get +/-45v.
But when the output amplitude near +/-25v.
I hear some "Tizz" sound.
when i increaer the input signal , the output amplitude get some pulse.
If i continou increase input signal , the dc protect working.

I probe my triangle wave output , the ramp through the ov get some pulse noise.
Is that effect my whole system??
 
Disabled Account
Joined 2004
titanchen68 said:
Hi,,
I have seen the report you write, it so good...!!!
But i still get some confuse !
i have to read it again , Thanks....

Thanks.

It's still not finished..... I'm running into problems that I'm sure other people have had when they look at these things. Mind you it's good to have a go and get it down in one place.

Don't believe all of it, I'm sure you wont. Certainly don't think of it as a 'final' answer. I'm just thinking about things.

Feel free to be 'confused'. There is a lot of stuff to go through there and my English is not very 'formal'.

Cheers

DNA
 
I add two 3v clamp zener diode in error-amp.
(The feedbck network still connect before LC-filter)
And i probe the output of error- amp , the highest amplitude is 3.5.
My triangle amplitude is 4v , i think the output amplitude must be 45v.
But I only get 28v , the output waveform get clip.
Even if increase the feedback resistor to 62K , It still get 28v.

Now , i don't have any ideal about why it happen.
 
I found something ...!!!
I probe the output of RC filter in feedback network.!!
I use 1k // 200p to do a LPF filter. Fc = 795kHz.
The waveform looks like only smooth the coner slightly,But only the top of rise eage and buttom of the fall eage.

When the output amplitude get higher , the duty cycle of the waveform,become high and low depend on the output amplitude.

when the output amplitude get higher , the amplitude of feedback waveform become lower , because the LPF in the feedback network smooth the rise eage coner.

so , i want ask how to design the LPF in the feedback network??
My triangle freq only 160KHz , doesn't 800KHz LPF too low ???
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.