mosfet output conversion

[engel dela pena]

can somebody help me converting a match pair mosfet output to a quasi design output or two npn output like 2sk1058 and 2sj201 my reason is i have lots of npn mosfet and i like to use it

 

[AndrewT]

Hi,
find a schematic that gives what you need.
The design shown is using the VAS to drive the FETs directly. I do not like this arrangement since it forces the adoption of big medium power transistors for Q3 to Q7 inclusive. Then these load up the LTP, also not good.
Get a better schematic.

Have a look at Quasi's designs. There are three or more threads covering all the detail of the design and build with a wealth of buider input and a superb web site put up by Quasi.

You did search "quasi", you cannot post without saying "yes".

 

[engel dela pena]

mosfet output

andrewt
thanks,for long i've been searching for quasi design,any comment on quasi's n-mos amp,i just wan't to use my n-channel fets,from surplus shop

 

[richie00boy]

What more comments do you want? He recommended the design to you. Have a look on the threads by quasi, they are full of information.

What MOSFETs have you got?

 

[jmbaudoin]

quasi comp

hello,

I have tried this output stage, good to me

http://perso.orange.fr/francis.audio2/C07_FB1a.gif

JMB

 

[ilimzn]

Re: quasi comp

hello,

I have tried this output stage, good to me

http://perso.orange.fr/francis.audio2/C07_FB1a.gif

JMB

Shouldn't that have at least some sort of thermal sompensation?

 

[richie00boy]

It uses lateral devices, so no need.

 

[ilimzn]

It uses lateral devices, so no need.

Really? Te top is a 'darlington' with a BJT in front so at best it will have zero Tc at well over 200mA, and the bottom is a CFP with BJT in front which has the TC of the BJT transistor. Have you simulated at different temperatures?

 

[slideman82]

Re: Re: quasi comp

Shouldn't that have at least some sort of thermal sompensation?

I've read power MOSFETs had negative thermal resistance... so, when, temperature clims up, its conductance goes down, or something like that, but I think that happens with audio output mosfets, the lateral ones, no t teh vertical, made for switching purpose, although you can use it on audio! They're cheaper too!

Thanks to Flavio Dellepiane, visit his site, please.

www.redcircuits.com

 

[jmbaudoin]

In my experience there is no need for thermal compensation with mos-fet bias between 0.3 to 0.7 Amps , thus motorola drivers had their own heather, and Mos where BUZ sort. used with 0.3 °C /W heather per chanel.

 

[AndrewT]

Re: Re: Re: quasi comp

I've read power MOSFETs had negative thermal resistance...

yes, go look at the graphs in the datasheets.
Compare Lateral to Vertical FETs and note that lateral change from positive to negative at around 100mA and that vertical change from positive to negative at enormous Amperes Id. They blow up before you can reach the negative coefficient.

Verticals need compensation. Laterals do not need it, but parallel sets do benefit from some feedback by fitting source resistors to each.

Ilimzn was referring to the uncompensated drivers.

 

[jmbaudoin]

Drivers have to dissipate less than 1 Watt with tipical 10 ma. bias so individual U-shaped heatsink can do balance with mos-fet thermal behavior.
The result can be DC offset less than 20mV hot/cold.

JMB

 

[engel dela pena]

ouput conversion

in regards to output stage conversion if michael chua of ampslab practice this to bipolar maybe it can be done also to mosfet compare this attachment we will notice that the only difference is the the output stage

 

[engel dela pena]

attachment 2

attachment 2

 

[richie00boy]

Why don't you build that then? The circuit in your first post is not really suited to easy converting to n-channel mosfet by beginners.

 

[kASD]

Driving N-Channel Mosfet QC amp just like a regular bipolar QC amp is one of the biggest mistakes conducted by Diyers🙂