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Old 8th December 2009, 10:14 AM   #31
PHEONIX is offline PHEONIX  Australia
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Quote:
Originally Posted by panson_hk View Post
Output at 18 W into 8 ohm. THD vs time from a cold start. It takes about 20 min to reach the min. THD level (optimum set point).

Bias scheme: Two ThermalTrak diodes in series with a 1 k pot.
Hello Panson_hk

Why dont you plot 20-20Khz THD curve into 8R with 80Khz bandwidth and 18W and 80Watts.

Regards
Arthur
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Old 8th December 2009, 12:07 PM   #32
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Hello Panson_hk

Why dont you plot 20-20Khz THD curve into 8R with 80Khz bandwidth and 18W and 80Watts.

Regards
Arthur
Please visit my web site for such curves.
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Old 8th December 2009, 01:32 PM   #33
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Hello Panson,

about possible compensation optimization. Have you tried it?
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Old 9th December 2009, 05:22 AM   #34
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Hello Panson,

about possible compensation optimization. Have you tried it?
I have not tried other compensation yet since I am doing bias tracking improvement for ThremalTrak.
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Old 14th December 2009, 06:55 AM   #35
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Default Two channels in a case.

Two-channel compact 49810 TT in a case under testing.
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Old 14th December 2009, 03:14 PM   #36
traw is offline traw  United States
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When using a driver like mje15030/31, in my case pushing 3 set of irfp240/9240, is there a rough calculation of how much the drivers should be biased to? Or is it an adjustment by monitoring a scope ? With 53volt rails, and 400 ohms strung from 15030 emitter to the 15031 emitter get 7.39 volts for about 18mA. Seems that voltage is fixed based on how much biasing the output stage, ~150-200mA I am using. Then the bias current through the driver just manipulated with that resistor since the 7.39 for me seems fixed based on that power stage bias choosing.

Just wondering if there is a rule of thumb...
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Old 15th December 2009, 02:16 AM   #37
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Originally Posted by traw View Post
When using a driver like mje15030/31, in my case pushing 3 set of irfp240/9240, is there a rough calculation of how much the drivers should be biased to? Or is it an adjustment by monitoring a scope ? With 53volt rails, and 400 ohms strung from 15030 emitter to the 15031 emitter get 7.39 volts for about 18mA. Seems that voltage is fixed based on how much biasing the output stage, ~150-200mA I am using. Then the bias current through the driver just manipulated with that resistor since the 7.39 for me seems fixed based on that power stage bias choosing.

Just wondering if there is a rule of thumb...
Hi traw,

We shall bias driver in class-a, i.e. the current never stops. Since you are using MOSFET output, you don't need to worry about the current value for class-a operation. The driver is always in class-a mode.

The simulation confirms that gate current is so little to pull driver output of class-a mode.

On the other hand, we need some calculation for BJT output.
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Old 15th December 2009, 04:01 AM   #38
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I guess the thing i wonder is how much current should I run through the driver? Your sim seems to show 45mA. I am currently using about 18mA with 400ohm R4. I started with 200ohm R4 and was at 36mA and mje1503X devices were getting quite warm (have slip on to220 heatsinks on them). Not sure if should drop down to even lower mA by increasing R4 or need to have more current running through - ideally little as needed to do the job and most performant of course. thanks
I do like the sound using driver with the IR mosfets better than driving straight off lme, using lme49830 though.
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Old 15th December 2009, 04:15 AM   #39
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I guess the thing i wonder is how much current should I run through the driver? Your sim seems to show 45mA. I am currently using about 18mA with 400ohm R4.
45 mA in the sim is just an arbitrary value. The main point is that the current is practically constant. You can set it according to sonic performance and heatsink requirement.

You compared sonic performance between 49830 and 49810+driver?
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Old 15th December 2009, 04:20 AM   #40
traw is offline traw  United States
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Originally Posted by panson_hk View Post
You compared sonic performance between 49830 and 49810+driver?
It was sonic impression of 49830 running 4 fets directly versus running 6 fets with a driver, liking the latter better.

Ah ok... I thought maybe there was some rule of thumb could use to choose right ballpark of current, guess experiment away. Need to get scope.

Have not tried 49810. Boards I have made for 30, though tried once to tweak for some sample 49810 with failure and just shelved the experiment - not sure what missed as thought diff was just need to feed another pin with 5volts or something like that.
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