I have a blown kicker kx1200.1. One side of the PS FET's were blown, along with its associated driver and channel on the TL494. After looking through a couple of the threads on here, it appears I have a different version of the PCB. For starters, it appears that other people have the gate driver transistors for the power supply being labelled as Q05 and Q11. In the other threads they seem like they are SOT-23 parts using the MMBTA56 as a substitute part. On my board, it looks like Q10 and Q16 are the drivers and they are TO-92 PNP transistors. I cannot find Q05 or Q11 anywhere near the TL494 chip. Has anyone else ran into this? Are these the only gate drivers or are there another two for a push-pull configuration? I do not see any other TO-92 parts.
Also looking to find a substitute for the drivers I did find. The parts are labelled:
Q10:
K232
A1266
GR
Q16:
K044
A1266
GR
It looks like the original part was a KEC KTA1266GR. Does this sound correct? Fairchild lists the KSA1015GR as a direct replacement. Are there any other replacements or upgrades I could use?
Lastly, everyone seems to have IRF3205's as the PS FET's with 47ohm gate resistors. The one I have had IRF3205's with 22ohm gate resistors. I realize this probably helps drive the IRF3205's harder, but is it normal? I am not sure if I should look for upgraded current handling in my driver transistors.
Also looking to find a substitute for the drivers I did find. The parts are labelled:
Q10:
K232
A1266
GR
Q16:
K044
A1266
GR
It looks like the original part was a KEC KTA1266GR. Does this sound correct? Fairchild lists the KSA1015GR as a direct replacement. Are there any other replacements or upgrades I could use?
Lastly, everyone seems to have IRF3205's as the PS FET's with 47ohm gate resistors. The one I have had IRF3205's with 22ohm gate resistors. I realize this probably helps drive the IRF3205's harder, but is it normal? I am not sure if I should look for upgraded current handling in my driver transistors.
There are 2 versions. The red board used 100 ohm resistors. The green board used 22 ohm resistors.
The gate resistor value depends on several things. In an amp without additional dead time programmed into the drive circuit, the 47 ohm resistors are generally a good value. With additional deadtime, the 100 ohm resistors can be used. The 22 ohm resistors will work with the 3205s as well.
The 1266 was the original part.
The 1015 seems to be essentially identical. It should be a good substitute.
The gate resistor value depends on several things. In an amp without additional dead time programmed into the drive circuit, the 47 ohm resistors are generally a good value. With additional deadtime, the 100 ohm resistors can be used. The 22 ohm resistors will work with the 3205s as well.
The 1266 was the original part.
The 1015 seems to be essentially identical. It should be a good substitute.
OK thanks guys. I had blown PS FET's, drivers, and one channel of the TL494. I do not have any subs for the drivers right now, but after I replaced the TL494, I got my clean square waves back. Each pulse was ~20uS with ~3uS of deadtime between pulses. Keep in mind this was without the drivers or PS FET's. I think my deadtime is sufficient. I am going to be replacing the PS FET's with IRFB3306 using 22 Ohm gate resistors.
To verify, there is only one PNP gate driver transistor per side, correct?
To verify, there is only one PNP gate driver transistor per side, correct?
It is because it is what I have on hand. I used these on a previous amp with no issues as a substitute. Actually, as I look at the specs, it looks like the IRFB3306PBF is easier to drive than the IRF3205PBF. What specs in particular lead you to believe that the 3306 is harder to drive than the 3205? Maybe I'm missing something.
OK, I see that. Isn't gate charge a better indicator of how hard a transistor needs to be driven? I seem to remember having talked to an app engineer at IRF about this once before about a year ago when I was working on a circuit for my job. He pointed me to their following app note: http://www.irf.com/technical-info/appnotes/an-944.pdf
In there, this is what I took out of it (quoted on page 5):
As this application note shows, of “bottom line” importance is the total gate charge required for switching. The lower the charge, the lower is the gate drive current needed to achieve a given switching time.
I hope you don't think I'm trying to be difficult, I'm just trying to learn
In there, this is what I took out of it (quoted on page 5):
As this application note shows, of “bottom line” importance is the total gate charge required for switching. The lower the charge, the lower is the gate drive current needed to achieve a given switching time.
I hope you don't think I'm trying to be difficult, I'm just trying to learn
I could be wrong but in all instances that I've encountered for 'power supply FETs', the Ciss seemed to coincide with the amount of drive current required to properly switch the FETs on/off.
I constantly have people trying to modify or improve circuits designed by professionals. Many times, it leads to a lot of time troubleshooting and, in the end, they end up using the correct part. People, many times, wrongly assume that they have improved a circuit in some way but they lack the ability or desire to properly test the circuits under all possible operating conditions so they don't 'really' know if the circuit is performing better (or even operating properly). They simply feel good because they believe they are better/more intelligent than the people who make a living doing design work.
I've seen too many instances where simply changing an op-amp (something too many people want to do) caused problems that weren't immediately obvious. Using substitute parts in class D output stages causes even more problems.
I've found it best to use the proper parts, as long as they're still available.
I constantly have people trying to modify or improve circuits designed by professionals. Many times, it leads to a lot of time troubleshooting and, in the end, they end up using the correct part. People, many times, wrongly assume that they have improved a circuit in some way but they lack the ability or desire to properly test the circuits under all possible operating conditions so they don't 'really' know if the circuit is performing better (or even operating properly). They simply feel good because they believe they are better/more intelligent than the people who make a living doing design work.
I've seen too many instances where simply changing an op-amp (something too many people want to do) caused problems that weren't immediately obvious. Using substitute parts in class D output stages causes even more problems.
I've found it best to use the proper parts, as long as they're still available.
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