HiFonics HFi1500D

[Tom7227]

Hi Guys,

Working on this amp and I have found that all the power supply FET's are shorted, along with the drivers.

The gate resistors are all charcoal, can anybody tell me the value?


And, the FETS are p55N06's, do you think a P60N06 should be ok to use?

Tom

 

[Tom7227]

Correction,

The Power supply FETS are 55NF06 's , Id like to sub with 60NF06's

Different Itotal?

 

[mika111]

Perhaps not all of the gate resistors are burned down, so take them of from board and try to measure resistance value from each of them. Maybe someone shows you the right value.

I think it should be somewhere between 22-220ohms.

That 60N06 would probably work....it depends a bit from the driver transistors and gate resistor values. 60N06 has little larger Qg and Ciss so these need more ´power´ from drivers.

I=Q/t

55N06 = 35nC/130nS = 0,27A
60N06 = 39nC/11nS = 3,54A

also relation of Rds and Qg

55N06 = 35nC/0,02ohm = 1750
60N06 = 39nC/0,018ohm = 2166

So......

 

[Tom7227]

I removed them from the circuit board and they read 27 ohms, so I will use 22 ohm, and I read another post that indicated that BD140 and BD 139 are good driver replacements.

Thanks for the info 🙂

 

[mika111]

Drivers could be also:

2N5192/2N5195 or BD179/BD180

 

[Perry Babin]

In photos I have here in board v1.3, they use 47 ohm resistors.

 

[Tom7227]

That's is the same version board I have, I wouldn't have thought that they would have burnt all to the same value... WTF

Do you think using the 60NF06 with 47 ohms should work?

 

[Perry Babin]

The 60NF... should work.

In all of this series/type of maxxsonics amps I use the 3205/47ohm/BD139/BD140 combination.

 

[Tom7227]

LOL, Love the "should"

I will let ya know

 

[mika111]

I think it would be better to use those 22ohm resistors with that 60NF.......maybe

Perry can fix this assuming if necessary 😀

 

[Perry Babin]

When I was younger, I would make all sorts of absolutely definitive statements. Now I know that there are variables that can't always be known and can cause things not to work quite as expected. That's why I rarely make definitive statements unless I have tested something thoroughly or otherwise have proof that something will work.

 

[mika111]

I did not make that gate resistor statement as a absolute true. I simply figured that out from 60NF06´s bigger Ciss and Qg values.

But better to stay on with components that manufacturer has placed there. Then there shouldn´t be any problems.

 

[Perry Babin]

mika111:
My post had nothing to do with what you posted. Your post came in between the time I started typing and the time I posted.

Looking at the datasheets for the IRF3205 and the STP60NF06, the Qg and the Ciss for the 3205 are much greater and the 3205s work with the 47 ohm resistors. The STP60NF06s would be a lighter load so there's no reason (that I can see) that the 47 ohm resistors wouldn't work with them.

 

[mika111]

My mistake..sorry. It was 3.00am here at that moment, so didn´t read everything properly 😀 But yes, should expect those 60NF´s to work if 3205s do work in same circuit.

 

[Tom7227]

Thanks to the both of you for your input on this issue. I installed the 47 ohm gate resistors, replaced the drivers with bd139, bd140 and finally 60NF06 (10 total). The Amp turns on and appears to function.

The question is, were would one find an issue if those gate resistors were incorrect or the FETs would not be compatible?

Would you expect to see the FETs over heat or would there be a problem when the amp drew a lot of current?.

 

[Perry Babin]

If the resistor value is too high, the FETs will overheat. Even idling 1/4-1/2 amp too high (due to the resistor value being too high) the FETs could become extremely hot quickly. This is often masked with regulated power supply drive circuits at idle because the duty cycle is reduced. At full power, the duty cycle increases and the FETs begin to cross-conduct. This makes them much more likely to fail prematurely.

If you choose a value that's too low, it stresses the drive circuit more (not really an issue with those drivers) but I've also seen it cause nasty switching transients on the FETs.