I just figured that with Idss of 10ma on the JFETs you get 20ma through the 1k and 25Vds on the JFETs. You might have to loose 2-3Vds through the cascade JFETs so you might get 22Vout. No other changes, the simple way...
Well, I was somewhat mistaken above regarding "no other changes". You will need to adjust the Resistors driving the gate of the cascode transistors for a slightly higher voltage. Where N.P. has 18V you will need about 5 more Volts there. You can get that by lowering the Rs on each rail or raising the Rs in the middle. I don't have a pic of the schez or I'd give the ref des for the Rs. It should be simple to calculate and get close. 😀
A balanced version with cascaded FE feeding folded output is done using smd parts. Don't know how popular the balanced or smd would be for general use.
Exactly - current supply resistors need changing in that case too. With changes shown in the sch. below I got about 28V_peak of clean swing at the output (I didn't dare to go higher since the J74's Vds reached 29V). The current through R2/R11 (1K) was 16 mA (about 6mA through JFETs and 10mA through BJTs).
Attachments
So Juma, what do you think of BJTs in the cascode position?. They are generally regarded, even by N.P. typically, as the better solution here. But, he chose to use more JFETs in this design?
Thx
Thx
I think they are the right tool for the job...
Yes, but they are so similar that it shouldn't be considered a mistake in this case.
OK 😀 A little marketing...
Thing is, I have BC550 etc, and Toshiba Js & Ks but, I don't have LS Js and Ks 😡
Antoinel, check this pdf http://www.circuitdiy.org/Datasheets/SKU17-1.pdf
Small signal devices don't have complementary, but K69/J19
Small signal devices don't have complementary, but K69/J19
Thank you massimo. This SIT pair will broaden the use scope of the circuit presented by Mr. Pass at BAF 2013. A complementary folded cascode SITs may have a lower Zo than that of analogous JFETs, and thus save an additional output buffer if it is low enough.
Feedback from the output of the Pass circuit to the gates of its FE may fit the practice of Schade or Pass feedback. Consequences are a lower voltage gain, but with a new triode-like characteristics if desired.
Do you need resistors on the bases of the BJTs for stability, or is that not a problem in this circuit?
Thanks to a nice person in Japan I have a few 2SK78B and 2SJ78B, SIT
complements, a couple hundred volts Vds, 0.5 amp and higher power.
Unfortunately, I do not know how to obtain more, otherwise they would be
sitting in a DIY project right now.
😎