This RF came in with defective power supply and amplifier right channel. Left channel is working normal.
Replaced in R channel:
5x IRF9640
5x gate resistor 100R
2x 0,1 ohm source resistor
power supply:
4x 75N05 to IRF 1405
4x gate resistor
Amp still not working: with high current draw >10A.
IRF1405 are hot with in 5 sec.
With the rectifiers MUR 1620 removed still >10A idle
With the rectifier diodes for the 17V LM317/LM337 supply removed at the right channel idle is 1,5A, which is very strange to me because two transformers are in parallel. And +/- 17V are still there on both channels.
My question is, are the MTP75N05 exchangable with the IRF1405 which i had on stock? I measure some overshoot at the gates.
Replaced in R channel:
5x IRF9640
5x gate resistor 100R
2x 0,1 ohm source resistor
power supply:
4x 75N05 to IRF 1405
4x gate resistor
Amp still not working: with high current draw >10A.
IRF1405 are hot with in 5 sec.
With the rectifiers MUR 1620 removed still >10A idle
With the rectifier diodes for the 17V LM317/LM337 supply removed at the right channel idle is 1,5A, which is very strange to me because two transformers are in parallel. And +/- 17V are still there on both channels.
My question is, are the MTP75N05 exchangable with the IRF1405 which i had on stock? I measure some overshoot at the gates.
The 1405s are harder to drive. You may have to go to a lower value gate resistor.
If you had open source resistors, you very likely have damage to the protection circuit.
If you had open source resistors, you very likely have damage to the protection circuit.
Thanks for answering Perry. I will try the lower gate resistors.
75N05 is obsolete overhere...and I saw you recommend IRF3205 or IRF1010e in another thread. But then I have to do the mesha trick again..🙁
75N05 is obsolete overhere...and I saw you recommend IRF3205 or IRF1010e in another thread. But then I have to do the mesha trick again..🙁
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I use IRF3205 and 47 ohm gate resistors. You may want to replace the drivers in the power supply as well if you have not already.
Lowered the gate resistors to 47 ohms, less overshoot (just a bit), amp is working again! 🙂
I was reading both datasheets of the IRF1405 and 75N05, are there other parameters for the switching behaviour, because their difference is not that big..?
IRF1405
Rdson 4,6mOhm
Ciss 5480pF
Coss 1210pF
75N05
Rdson 6mOhm
Ciss 4500pF
Coss 1100pF
I was reading both datasheets of the IRF1405 and 75N05, are there other parameters for the switching behaviour, because their difference is not that big..?
IRF1405
Rdson 4,6mOhm
Ciss 5480pF
Coss 1210pF
75N05
Rdson 6mOhm
Ciss 4500pF
Coss 1100pF
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The numbers for the 75N05 are off. See attached.
Many years ago, the Ciss was considered the determining factor when looking at the load on the drive circuit. It was prominently listed on the top of the datasheets. Now Qg (total gate charge) is considered more important. From my experience, for power supply FETs, the Ciss seems to be more critical but since both parameters increase as the current rating increases, you can look at either when comparing parameters for substitutes for power supply FETs. For output transistors in class D amps, I haven't found it as simple to determine which transistors would be more suitable from datasheets.
Many years ago, the Ciss was considered the determining factor when looking at the load on the drive circuit. It was prominently listed on the top of the datasheets. Now Qg (total gate charge) is considered more important. From my experience, for power supply FETs, the Ciss seems to be more critical but since both parameters increase as the current rating increases, you can look at either when comparing parameters for substitutes for power supply FETs. For output transistors in class D amps, I haven't found it as simple to determine which transistors would be more suitable from datasheets.
I was looking at datasheet of the the SUP75N05 http://www.mouser.com/ds/2/427/70292-240088.pdf with differences to the MTP75N05.
Qg more inportant? ok thanks!
Qg more inportant? ok thanks!
I still look at the Ciss for PS FETs. As with any substitute, you have to test thoroughly. That's why I recommend reducing the 12v supply voltage to force the supply to full duty cycle to see if the current draw increases at the lower voltage. If it does increase, the drive circuit has to be modified to work with the substitute FETs.
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