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Old 26th January 2008, 09:05 AM   #11
AndrewT is online now AndrewT  Scotland
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Hi Gaet,
the 0r15 is far too low. It will overheat the MJE drivers.

I would still use 4diodes (1 from each output) but you may want to experiment with adding a small resistor value to the emitter of the BD139. Someone symmed this recently and reported good results.

Have you looked at the interview threads - fets includes a section on using diode compensation?
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Old 26th January 2008, 12:46 PM   #12
roender is offline roender  Romania
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Hi Gaetan,

With only 4 diodes output stage will be undercompensated and on a verge of runaway:
4*(-1.66) = -6.64 mV/K Total TC for NJL diodes.
4*(-2.1m) = -8.4mV/K Total TC for drivers (CFP) and output BJTs BE junctions.
The output stage will have a total TC = -2.24mV/K !!!!!
You need five NJL diodes with total TC = 8.3mV/K

Mihai
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Old 26th January 2008, 12:48 PM   #13
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Quote:
Originally posted by AndrewT
Hi Gaet,
the 0r15 is far too low. It will overheat the MJE drivers.

I would still use 4diodes (1 from each output) but you may want to experiment with adding a small resistor value to the emitter of the BD139. Someone symmed this recently and reported good results.

Have you looked at the interview threads - fets includes a section on using diode compensation?

Hello Andrew

I want to keep the drivers allway ON in class A, to minimize switching noise, so what would be the minimum value to replace the 0r15 resistor ?

How about 50 ohm for small resistor value to the emitter of the BD139 ?

You mean to look at the "Bob Cordell Interview: BJT vs. MOSFET" ?

Thank

Gaetan
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Old 26th January 2008, 12:51 PM   #14
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Quote:
Originally posted by roender
Hi Gaetan,

With only 4 diodes output stage will be undercompensated and on a verge of runaway:
4*(-1.66) = -6.64 mV/K Total TC for NJL diodes.
4*(-2.1m) = -8.4mV/K Total TC for drivers (CFP) and output BJTs BE junctions.
The output stage will have a total TC = -2.24mV/K !!!!!
You need five NJL diodes with total TC = 8.3mV/K

Mihai
Hello Mihai

Can I ad a 1N4148 for the fifth diode ?

Thank

Gaetan
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Old 26th January 2008, 12:53 PM   #15
roender is offline roender  Romania
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Quote:
Originally posted by gaetan8888

watt would be the minimum value to replace the 0r15 resistor ?
Thank

Gaetan

15ohm will bias drivers at 75mA
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Old 26th January 2008, 12:57 PM   #16
roender is offline roender  Romania
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Quote:
Originally posted by gaetan8888


Hello Mihai

Can I ad a 1N4148 for the fifth diode ?

Thank

Gaetan
No, use a MUR120. Put all output stage junctions on the same heatsink ... take a look at RMI-FC100 thread. Or use three NJL pairs
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Old 26th January 2008, 01:02 PM   #17
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Quote:
Originally posted by roender


No, use a MUR120. Put all output stage junctions on the same heatsink ... take a look at RMI-FC100 thread. Or use three NJL pairs

Hello Mihai

I have some 1N5819 , can I use that ?

Thank

Gaetan
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Old 26th January 2008, 01:06 PM   #18
roender is offline roender  Romania
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Do not know. If TC=1.66mV/K you could try.
MUR120 is the diode inside NJL transistor.
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Old 26th January 2008, 03:27 PM   #19
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Or you can use a 4 units endstage and just use the diode on a fifth one.

Reason is you only get 5 Pieces of each as sample from ON Semi
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Old 26th January 2008, 04:32 PM   #20
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Quote:
Originally posted by Radioman62
Or you can use a 4 units endstage and just use the diode on a fifth one.

Reason is you only get 5 Pieces of each as sample from ON Semi

Hello

I should do that, as you guess I did get 5 Pieces of each as sample from ON Semi, at least the fifth NJL will be at good use.

They don't have those NJL at Mouser.com but they have the MJL version only.

Thank

Bye

Gaetan
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