IRFP240/9240 -Vbs,Drivers ??? - Page 3 - diyAudio
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Old 1st April 2005, 05:12 PM   #21
ilimzn is offline ilimzn  Croatia
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Sto te zanima, nesto ekstra klase ili nesto OK, jednostavno i pouzdano? Imam nesto s IRFP240/9140...

Sorry for the non-English content everyone, zox is enquiring about an amp schematic. I will look into my archive and post something when I get home from work...
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Old 1st April 2005, 05:17 PM   #22
zox2003 is offline zox2003  United States
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Default OK

Vise bi mi odgovaralo to sto je jednostavnije i pouzdano znaci nesto sto si mozda probao i radi bez problema.
Imam 2 x 42V ispravljac.

Ja bih te zamolio ako mozes da postiras danas.

Hvala Unaprijed...


I am sorry...We are just guys from same country and sometimes is easier to communicate on our language.I asked him to post schematic today for amp I requested.
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Old 1st April 2005, 06:24 PM   #23
ilimzn is offline ilimzn  Croatia
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Here is a simple amp I've built many times...

Notes:
Q6, 7, 8 will work best with some small heatsinks. I used a double sided PCB with ground plane on top and just bent the transistors to lie on it, with a drop of heat transfer grease between the transistor body and the copper. It will work with no heatsink but the transistor temperatures will be about 60C. Q6, 7, 8, 10 may be changed for something in a case more suitable for cooling but I would not recomend it because most transistors in cases like that have lower gain. There is a better way to solve this, see below under improvements.

Q1, 2, and 3 are mounted on appropriately large heatsink. Mount Q1 between Q2 and Q3 if Q2 and Q3 are close, else mount Q1 close to either Q2 or Q3 if Q2 and Q3 are further apart.

R1 = 10k trimmer has '40%' beside it because that was left from the simulator. It sets bias current, wiper towards Q8 increases bias current. About 25mA will minimise distortion into 8ohms resistive at 1kHz but will have unreasonably high HF distortion. Depending on application I use from 40-150mA.

Although not obvious, R7, R6, D3 form a current limiter which is quite symetrical for both N and P output MOSFET. Changeing of the power devices will require changes in their values, so know what you are doing before you change this!

Some things not shown on the schematic:

No Zobel/Boucherot network has been included in the schematic. When configured as a standalone amp, i normally include it, typical examples are easily found.

Input cap - if DC coupling is used from a low impedance source, change C3, R4, R8 to 470u, 3.3k 2W, 100ohm respectively. If input cap is used, leave as is. This reduces output offset voltage.

Power rails to output tansistors need fuses. 4A fast blow max for your power rails. you can push it higher, IRFPs are quite robust, but be careful. Output current limit is set to about 8-9A. If you trust your fuses, you can remove the zener...

Possible improvements:

Small non-inductive foil caps should be placed in parallel with C1, C2, C3, C4 and input cap if used (if it's not a foil type already).

Remove diodes D1 and D2 and feed the driver stages with regulated 40-45V for better output power.

Use higher gain transistors for Q5 and Q6 (BC546B work well but R23 and R24 may need increasing so that Vcemax for BC546 is not compromised under any circumstances). The distortion will lower somewhat.

D4 and D5 may be replaced by a LED (R20 may have to be changed to keep the current through Q9 more or less the same).

Q4 and Q5 will be slightly unbalanced in this circuit due to the simple current mirror used. This increases distortion a bit and introduces 20-30mV of output offset. If offset is a problem, R22 can be slightly lowered by paralleling with a large (10k or so) resistor, to correct this. A wilson current source is the real answer but then it makes it a different amp

Increasing driver stage current will reduce distortion but since the LTP tail current is the reference, this can get complicated. Also, Q6, 7, 8 heat can become a serious problem. There are two ways to solve this:
Add a 'shadow' pair to R13, Q7, Q8, R21
Add cascode transistors to Q6, Q7, Q8
I've done both but then this becomes a different amp, so that's a nother story

Distortion will be lower if R2 and R5 are lowered, or removed entirely. If you remove them replace R6 by 100ohms, a zener diode must be added between gate of Q2 and output, both zeners should be about 5.1-5.6V. Thermal coupling between Q1, 2, 3 must be done carefully (use good insulators and grease, also mount transistors mechanically close). You also get increased output power. You may want to increase R18 to avoid accidentally being able to set an extremely high bias current. In any case, meddling with R2 and R5 requires change of the zener diode to get appropriate current limiting.

Expect a good clean 60W under all circumstances from this amp, with plenty headroom.
Attached Files
File Type: pdf mosfet.pdf (12.7 KB, 449 views)
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Old 1st April 2005, 06:30 PM   #24
zox2003 is offline zox2003  United States
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Default Jos neki...

da li imas jos koji?



Any more?



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Old 1st April 2005, 06:33 PM   #25
zox2003 is offline zox2003  United States
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Default What about 4 ohms

Can I run this amp on 4 ohms?How much more power I will get?

Can I replace IRF520 in your schematic with BJT transistor?

Thanks
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Old 1st April 2005, 06:58 PM   #26
zox2003 is offline zox2003  United States
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Default Question about upgrade

What if I add driver stages ?Any better and more power?
Check attachement with mods and let me know?

Thanks.
Attached Files
File Type: pdf amp mod.pdf (25.5 KB, 264 views)
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Old 1st April 2005, 07:01 PM   #27
edl is offline edl  Hungary
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http://www.audiofanatic.it/Schemi/Ti...W_IRF530_1.jpg
http://www.audiofanatic.it/Schemi/Ti...W_IRF530_2.jpg

these are lookin' like IR's simple design.
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Old 1st April 2005, 07:57 PM   #28
ilimzn is offline ilimzn  Croatia
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Default Re: Question about upgrade

Quote:
Originally posted by zox2003
da li imas jos koji?
Any more?
Naslo bi se, ali polako - nismo u onom vicu 'nakapajte mi rezervoar benzina jer kap ne kosta nista'

Quote:
Originally posted by zox2003
Can I run this amp on 4 ohms?How much more power I will get? Can I replace IRF520 in your schematic with BJT transistor?
Thanks
Double power into 4 ohms but you are asking for trouble because unless you have a huge heatsink and/or you intend to drive simple loads (not very reactive) you will be operating the output transistors close to maximum.
In theory, IF you supply the driver stage with at least 10V more than the output stage, you can get the output to go within fractions of a V of the rail voltage, but distortion will rise a lot for those last few V. So, with 40V rails into 8 ohms, assuming rail voltage does not droop, you get 100W into 8 ohms. THEORETICALLY 200 into 4 but you will need a HUGE heatsink and special mounting hardware to do this semi-reliably. I would not recomend more than 100W-120W continious out of one pair of IRFPs into any load. You could use multiple pairs but you need a driver stage for this. Alternatively, you can build two and bridge them, but I would recomend a lower output rail voltage (36V or so).

You cannot replace the IRF520 with a BJT, not without modifying nearby components. You could however use IRF530, 540, 640 instead, almost any MOSFET rated for at least 10A (the reason is higher transconductance in higher current types). If you want to use a BJT you will have to do a lot of experimenting with a resistor in the emitter and R2 and R5.

Quote:
Originally posted by zox2003
What if I add driver stages ?Any better and more power?
Check attachement with mods and let me know?
Thanks.
You cannot get more power with any kind of driver stage as power is limited by the output rail voltages and voltage/current/power ratings of Q2 and Q3.

The power you get out of the amp is defined by the voltage on voltage at C1 or C2 (max power rail - 0.5V) minus Vgs for the MOSFET at maximum current (about 5-7V depending on load) or the power rail voltage in that instant minus same 5-7V, whichever is lower. The power will be that voltage squared divided by 2xRload. Power rails should not be higher than 50V for the output stage AT ANY TIME for the given Q2 and Q3.

A driver stage may help if you want parallel MOSFET pairs, because the unmodified driver will not be able to drive more than one pair. In that case you need to connect the driver transistor collectors AFTER the diodes D1 and D2, and disconnect R6/R7 from the IRF520. Bases of drivers go to the point where you just disconnected R6 and R7. Emitters go to R6/R7 instead of the IRF520. Your R? in the schematic should be on the order of 150ohms. Drivers should be on heatsinks. C1 and C2 should be increased to 1000uF. Add 2 diodes in series with IRF520 drain, the diodes whould be in thermal contact with drivers (ideally). For this configuration a BJT instead of IRF520 could work better but still you need to change resistors around it and a resistor in the emitter of this BJT. Such a modified output stage can drive 2-3 pairs of MOSFETs.

From your questions and proposed mod I have to surmise you don't completely understand how this amp works, so I would advise starting small and with a proven design such as it originally is, before you start modding.
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Old 1st April 2005, 08:30 PM   #29
zox2003 is offline zox2003  United States
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Default Thanks...

Thanks you on your answers.You are helpfull.

Let's sumarize:

With same circuit as your original can I get 100w/4ohms on +/- 42V rails without any modifications (as is)?

Do I have to possible reduce something to have this amp running that power?


Can I exclude R2 and R5 for just a pair of IRFP240/9240?

Can I use IRFP9240 instead 9140?


Thanks a lot.


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Old 1st April 2005, 09:12 PM   #30
ilimzn is offline ilimzn  Croatia
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Default Re: Thanks...

Quote:
Originally posted by zox2003
Let's sumarize:
With same circuit as your original can I get 100w/4ohms on +/- 42V rails without any modifications (as is)?
Yes - a quick sim shows you will get 100W into 4 ohms if the rails do not drop below 36V at full load. Just use a big heatsink!!!

Quote:
Do I have to possible reduce something to have this amp running that power?
No, you have to increase - the heatsink

Quote:
Can I exclude R2 and R5 for just a pair of IRFP240/9240?
Yes, but be careful with thermal coupling. IF your heatsink is too small or thermal interface between transistors and heatsink is not good, you will have thermal runaway, and quickly!!!
On the other hand, excluding R2 and R5 alow for a bit more power, or more rail droop. You can get 100W into 4 ohms if rails do not drop below 33V or if, as above you alow for drop to 36V, you get 120W.
Also, you need to set both gate damper resistors to 100 ohms and put a zener in parralel with G-S of both MOSFETs, 5.1-5.6V.
The single zener limiter works by using the bias voltage and drop on R2/R5 as part of the limiting circuit, without R2/R5 it needs to be different obviously.

Quote:
Can I use IRFP9240 instead 9140?
You can use anything you want but there is no guarantee it will work OK, just kidding...
IRFP240 in this application robs you of about 1.5V of headroom, but just on the negative half-period which means you get less power and more heat, and asymetric clipping. You also get up to 50% more distortion in any case. Also, at 100W into 4 ohms you will be operating the 9240 right at the edge. Also, you need to modify the current limiting zeners because 9240 needs more voltage at input for same current as 240. 9140 does not.
That 9140 was not chosen for nothing
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