Pafi said:
thanks for that.
however, I fail to see how that helps substantiate your claim that
what exactly did you mean by that? if I load a 7.99ohm load to it (it is "lower" than 8ohm spec'd for the amp), would it explode? would it distort 10%? would it fail to produce any signal?
what exactly did you mean by "cannot be loaded", and how low is "lower impedance"?
I think you pointed an interesting and real phenomenon. I experienced a failure wich can only be explained by this. However I can't accept that an explosion can be occured without (at least local) overheating. 😉
Eva said:
The amp modifications needed to make tk2350 produce highest power include doubling the amount of mosfets as I've read (don't shoot the messenger...) from 4 to 8 mosfets....
fokker said:
The lower the load impedance, the higher the peak current the MOSFETs (and their body diodes) are required to handle and the amounts of heat produced.There is obviously a limit on the stress they can whitstand.
Pafi said:
Oh, "local overheating", I fully agree, I will try to remember that funny euphemism the next time that I have to explain a cracked transistor 😀😀
BTW: I'm working in class D full bridge fed with 300V to 400V and I experience that failure all the time with MOSFETs. I'm employing soft switching and di/dt is limited by means of a magnetic snubber, also the energy due to Qrr is returned to the supply instead of being dissipated. However, I have yet to find a MOSFET capable of surviving crossover times in the 50ns range (400V to 500V) after diode recovery, even Infineon "C3" series fail. Co-pack IGBTs perform just fine, though. I have just got some Infineon "CFD" devices to test (expensive!!)
Eva said:
I absolutely understand that and agree with that.
However, why was Pafi so sure that when a the amp cannot be loaded with lower impedance? how did he know that such a limited will be exceeded with an undefined impedance figure?
for example, is that limited exceeded with a 7.99ohm load? or 4ohm load? or 1 ohm load? or 0.1ohm load? Pafi hasn't been able to answer that and to me he could only be able to answer if he had tried his hands on the amp - something he apparently hasn't done.
All I wanted to know was what exactly did he mean by his statement and how did he learn that.
If you're prepared to sacrifice on power, with dropping the voltage any amp can drive lower impedance loads. Or: any amp driven to the limits of voltage can't drive heavy loads anymore...
As I said: "There is no point in calculating exact impedance. It depends on cooling, type of audio signal, etc..."
I'm not going to calculate exact impedance limit (wich is a function of several variables) especially since I dont know the circuit. All I said that there is a limit, and this limit is strongly affected by Qrr.
I'm not going to calculate exact impedance limit (wich is a function of several variables) especially since I dont know the circuit. All I said that there is a limit, and this limit is strongly affected by Qrr.
You're damned right, things can go well for a while, till the 'right' piece of music comes along to create an impedance beond amp tolerance.....
Pafi said:
Maybe Qrr is important for you but it isn't rigid here. My power stage is half bridge with additional diode. No more power lost because of Qrr. If amps are so easy damaged what is the purpose that we design complex protection circuit?
you said earlier and I quote:
so, doesn't that suggest that there exist lower impedance that when loaded to the amp, it will NOT cause the amp to exceed the limit and the amp will continue to work as designed?
if so, isn't that exactly the opposite of what you said?
Alternatively, find an amp that such a limit doesn't exist. If your earlier statement is true, it must be universally true and applies to UcD, NCD or any other amps and I didn't see you making that statement.
I am perfectly fine with making a wrong statement. Just clarify it and we move on.
Pafi said:
so, doesn't that suggest that there exist lower impedance that when loaded to the amp, it will NOT cause the amp to exceed the limit and the amp will continue to work as designed?
if so, isn't that exactly the opposite of what you said?
Alternatively, find an amp that such a limit doesn't exist. If your earlier statement is true, it must be universally true and applies to UcD, NCD or any other amps and I didn't see you making that statement.
I am perfectly fine with making a wrong statement. Just clarify it and we move on.
It looks like the discussion went very far from D-class amps 
. Can we go back to it?
Drzhuang, are these amps used in any commercial products (especially in PA systems)?
Can they be purchased in China (for example in Beijing)?
Marek
. Can we go back to it?Drzhuang, are these amps used in any commercial products (especially in PA systems)?
Can they be purchased in China (for example in Beijing)?
Marek
This is the third time I have to split off-topic posts.
I've got a job that takes part of my time as well.
Or you guys stay on topic, or I'll close the thread.
You've been warned.
/Hugo
I've got a job that takes part of my time as well.
Or you guys stay on topic, or I'll close the thread.
You've been warned.
/Hugo
Markus2006 said:It looks like the discussion went very far from D-class amps
Drzhuang, are these amps used in any commercial products (especially in PA systems)?
Can they be purchased in China (for example in Beijing)?
Marek
I'm sorry for disturbance ordinary discussion.
Actually, I didn't mean you in my post 🙂 . What about the questions I asked?drzhuang said:
Marek
Markus2006 said:
Yes, I understand you clearly. That "sorry" is for all who take care of the topic. But you know that the topic started in disputation. I can't answer you question here. Sorry. This is for you.
Pafi said:
Sine wave, resistance load, DC current meter and DC voltage meter for power supply£¬ AC voltage meter for load. In rated output power get data then calculate.
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