Some questions reg. ESP P3A

[Stormo]

Hi there,

I have built a version of ESP P3A with at MOSFET output stage.

2 questions: 1) With 28 v rail I can get no more than 20v pp from the amp before it start clipping (in both halfes) - is that normal ??

2) i have simulated a 42 v rail version - but the voltage sving is the same as the 28 v version unless i change the relation between r4 (1k) and r5(22K) . Setting R5 to 40k will make the simulation swing nice. But i dont see any dokumentation for making this change in the description ?.

Can anyone explain ?

Regards, Stormo

 

[Switch247]

that would be because the amp was designed for a BJT output.
Mosfets are not the same, and the whole amp might have to redesigned.

Jake

 

[skaara]

Fets need higher voltage for the same output than bipolars..

 

[e96mlo]

Try using a higher voltage on everthing but the MOSFETs. This will increase your output swing and improve efficiency.

Could you post your schematic, please? It would be interesting to se.

/Marcus

 

[joensd]

hello,
i found this P3A amplifier modified for use with mosfets.
maybe you get an idea how he´s done it.
pcb layout is included.



http://www.geocities.com/sapitopt/60w.htm#top

 

[e96mlo]

Check out Nelson Pass's MOSFET Citation 12 on www.passdiy.com.

It is quasicomplementary but the article contains a lot of good information.

/Marcus

 

[peranders]

Stormo, if you use MOSFET's especially the vertical ones you will need approx 8-15 V MORE voltage at the gate than the supply voltage. Otherwise you can't get full power out. I used in my QRO project +-60 V DC for the MOSFET's and +-80 Volts for the driver. When you use this techinque it's important' to have diodes+zeners from the driver to the POWER supply. This creates nice clipping. The driver stage won't saturate with these diodes. The result of the diodes is the driver voltage becomes (in my case) 60+0.7+12= 72.7 V. I used 12 volt zeners.