sbeach
Active member
Hi,
I found a class-A MOSFET current boosting circuit on a headphone-oriented web site, thought it may be used successfully for some line amp circuits & have redrawn it ...
http://www.twin-x.com/groupdiy/displayimage.php?pid=305&fullsize=1
The circuit has two stages as shown: a voltage gain opamp stage followed by a separate MOSFET current booster. The idle current for the booster is set by the 150 ohm source resistor - in this case (-15v) & it provides 100 mA of current to the MOSFET source. Maybe a current source (BJT or LM337 & 12 ohm resistor) would work better. What do you think? Additionally, the 5k trimpot allows you to null out DC on the circuit's output.
I have a few questions about this circuit's use. As drawn the current booster is shown AFTER the opamp voltage gain stage. Would it be possible or advisable to include the current booster MOSFET within the opamp's feedback loop? I've seen that done in other types of source followers & assume it would be possible here. If so, what are the advantages / disadvantages of placing the current booster within the opamp's feedback loop? Any & all comments, etc. are welcome.
Skip Beach
I found a class-A MOSFET current boosting circuit on a headphone-oriented web site, thought it may be used successfully for some line amp circuits & have redrawn it ...
http://www.twin-x.com/groupdiy/displayimage.php?pid=305&fullsize=1
The circuit has two stages as shown: a voltage gain opamp stage followed by a separate MOSFET current booster. The idle current for the booster is set by the 150 ohm source resistor - in this case (-15v) & it provides 100 mA of current to the MOSFET source. Maybe a current source (BJT or LM337 & 12 ohm resistor) would work better. What do you think? Additionally, the 5k trimpot allows you to null out DC on the circuit's output.
I have a few questions about this circuit's use. As drawn the current booster is shown AFTER the opamp voltage gain stage. Would it be possible or advisable to include the current booster MOSFET within the opamp's feedback loop? I've seen that done in other types of source followers & assume it would be possible here. If so, what are the advantages / disadvantages of placing the current booster within the opamp's feedback loop? Any & all comments, etc. are welcome.
Skip Beach