Summary of the upper currents 117,7mA while lower currents 81,2mA i.e ~40mA difference (if I counted right). Driver current leakage through a gate resistor, broken Fet? Wouldn’t otherwise 12V Vgs on all lower Fets pull like no other considering there's no offset?
Edit: Or some other leakage, PCB etc.
Edit: Or some other leakage, PCB etc.
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Howdy,
a stubborn kind of oscillation can be expected in the loop formed by T10 and T12-14-16 due to massive phase errors.
a stubborn kind of oscillation can be expected in the loop formed by T10 and T12-14-16 due to massive phase errors.
Moschfet, T10 forms part of a standard quasi-complementary configuration, so if you care to elaborate that would be cool.
Nigelwright7557, too true. This is why I recommend a 10 ohm resistor here for testing, to minimise the problem.
The fuse location in this design is not good and an oversight on my part. In subsequent designs I have moved the fuse to behind the driver stage. Some Nmos 350 constructors have corrected this by cutting the relevant tracks and linking back to the driver stage.
Nmos 350 Mk2 (yet to be officially published) resolves this.
Cheers
Q
When i build my amplifiers i don't use the resistors in place of fuses, i just tie in a 0.1 ohm resistor in series with one rail to monitor current and slam on the full rail voltage, then i turn the bias up until i either get the desired reading or till the bias pot bottoms out.
This is my version of the quasi: http://i.imgur.com/ubY2e.jpg
This is my version of the quasi: http://i.imgur.com/ubY2e.jpg
I replaced the R21 with yellow LED-Anode from output and cathode against MJE350's emitter (T10). It burnes the resistor R22, when I set the biass above 10mA and the LED is starting to glow orange (to much current) above 0,7V across the 100 ohm resistor (the one that replaces the fuse)!
Hi,
the Complementary Feedback Pair can provide significantly lower distortion, but is very prone to oscillation. It works best with class A biased devices, multiple slaves are inappropriate. It´s not easy to elegantly cure the problems in this PA-style implementation. Increasing the quiescent current of the FETs would be highly desirable for stability, bandwidth and to improve the strongly nonlinear transconductance. In any case, this amplifier won`t produce a nice sound.
the Complementary Feedback Pair can provide significantly lower distortion, but is very prone to oscillation. It works best with class A biased devices, multiple slaves are inappropriate. It´s not easy to elegantly cure the problems in this PA-style implementation. Increasing the quiescent current of the FETs would be highly desirable for stability, bandwidth and to improve the strongly nonlinear transconductance. In any case, this amplifier won`t produce a nice sound.
Driving Vertical Mosfets specially NFET output stage with regular fashion topology used in bipolar amplifiers is one of the worst thing to do.
Instability will always occur in such implementation.
"Always"? Stability is easy to implement with good layout, adequate drive and control and the use of quality components. The percentage of issues vs the succesful builds for this series is pretty good especially considering the skill level of some of the constructors* (as these amps seem to have attracted).
With 54mA flowing through the negative rail gate resistor at idle, this amp is clearly faulty.
* I'm not referring to anyone in particular, but the simplicity of these amps has encouraged many first time amp builders.
Cheers
Q
Technically your "Another amplifier"[the another one with rail to rail] is much better than this, if we consider the performance and drive symmetry of the stage.
Cheers to Q 😉
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Hi people interested to improve NMOS....
please check schematic
is it worth to add this features or faulty design ?
1. VI Limiter about 10 A in Short circuit condition clamp the mosfet gate
2. Bootstrap, in NMOS350/500 for maximum output power
3. Split Rails to add Class H Step Driver (Step driver from apex H900 amp)
Arcam 200 use this VI Limiter and bootstrap in NMOS amp
could this work or firework ?
want learn a lot of to improve...
regards
please check schematic
is it worth to add this features or faulty design ?
1. VI Limiter about 10 A in Short circuit condition clamp the mosfet gate
2. Bootstrap, in NMOS350/500 for maximum output power
3. Split Rails to add Class H Step Driver (Step driver from apex H900 amp)
Arcam 200 use this VI Limiter and bootstrap in NMOS amp
could this work or firework ?
want learn a lot of to improve...
regards
Arcam VI limiter is a FAILURE in itself and also the place at which you have used is not appropriate, the clamping collector of limiter transistor should be connected to base of driver transistor at high side, whereas at low side it will get hard time clamping the gate due to constant drive from driver collector.
Mosfet gate is not like BJT base where you clamp the base and reduce current, in case of mosfet entering shortcircuit, even you apply the clamp, the DG miller cap will charge the gate to much higher value than the clamped voltage and smoke the mosfet in no time, this is the reason why this type of VI limiter is a failure in Mosfets.
Bootstrapping High side won't gave you any advantage because lower side is still a CFP half and will still exhibit a large voltage drop across DS terminal of Mosfet and thus failure to perform as Rail 2 Rail amp.
You cannot use Class-H step driver with this amplifier, the conceptual topology is in gross failure in itself, upon switching, the lower side CFP will break into oscillations and Smoke.
Sorry to say, it won't work.
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I can't understand the use of irfp450. This mosfet seems to be unsuitable for analog signal control. It has 2600pF gate-capacity and I don't believe that the gatedriver can drive it. Especially with a gateresistor with 27 ohm, this isn't switching power supply 😉
Why don't you use the irfp240? It fits much better.
Why don't you use the irfp240? It fits much better.
Your perception is wrong.........!!!
I can use any Vertical mosfet with CGS> 10000pF in Linear Applications provided you have a dedicated driver for it.
The way Mosfets are used by "BJT Amp designers" is a failure mode in itself.
APT20M18LVR is my favourite in Linear Apps😉
Don't forget that Gate is a capacitor which needs to be discharged ACTIVELY not just by a passive resistor.
Can I use VI Limiter like in quasi complementary BJT amp or doesnt work to protect Mosfets ?
If not how can I protect Mosfets in this amp Short circuit condition, can you draw small schematic ?
regards