choice of bipolar output transistors

[capslock]

The Sanken 2SA1186/2SC2837 are my favorite pair. They may have the lowest current and voltage rating of all Sanken LAPT, but they have 60 MHz f_T, good gain linearity and above all, a low cob capacitance of 110 pF (at 80 V). As they are increasingly difficult to source, I have begun looking for alternatives.

I stumbled on the Toshiba 2SA1093/2SC2563 (by the way, does anybody have a data sheet for the SC part?). They feature slighlty worse hFE linearity, but sport 90 MHz fT which is also incredibly flat with collector current). Cob of the PNP is given as 110 pF at 10 V, so it is probably even better than for the Sanken. Unfortunately, they have been discontinued and are even harder to source.

Toshiba go on in their selector guide about their improved high-MET process.

As a replacement, they give the A1941/C5198 pair which happens to be a 10 A part.

Even the A1940 which has exactly the same current rating as the SA1093 has higher Cob (260 instead of 150 pF). hFE linearity is equivalent on the high current end and maybe a tad better on the low current end (if you believe that it was not the data sheet artist at work). fT is given with 30 MHz but no plot is provided. IC vs. VCE looks just the same.

So what are the advantages of the new triple diffused process over the old PCT process?? I notice all the new Toshiba power parts only have 30 MHz fT. Are they maybe better than the data sheets suggest?

[capslock]

Looking at 2SA1302, it is easier to see that Toshiba did implement an improvement, even within the "triple diffused process":
The 2SA1943 has 30 MHz, 360 pF vs. 25 MHz, 470 pF in the 2SA1302. IC vs. VBE looks a little more linear in the newer part, and hFE linearity is a little flatter and flatness extends out a little farther now.

Comparing the 1943 to OnSemi MJL1302A, these may well be very similar parts. MJL has a max 600 pF vs. 470 pF typ in the 1943 which is probably as identical as one can get. hFE flatness looks very much the same. OnSemi do not give IC vs. VBE. They state a typical fT of 30 MHz at 5V, 1A for both PNP and NPN, but in contrast to Toshiba, they give also typical plots that contradict the tabular information. fT at 5V, 1A looks more like 40 MHz (1302) and 48 (3281), and the curves peak at 45 and 55 MHz.

As pointed out, there is no fT plot for the 1943, but there is one for the original 1302 which peaks at 28.

=> is there some hope that the new Toshiba parts are faster?

[dkemppai]

Hi,

I've been using the 1934 for a while. It seems to be a good part, but I do wish it was a little faster. I'm using it as a vas transistor, and have found it to be the slowest part in the amp.

If you locate a similar part that is faster, let me know... ...I'd be very interested.

-Dan

[pinkmouse]

In my never ending quest for knowledge I have not come across an amp design using bipolar output transistors. Any suggestions where I might find some schematics, so I can work out what you're all on about?


Thanks

[capslock]

Hi Al,

actually, bipolar output stages are the most common thing. As an exhaustive primer, have a look at: http://www.dself.demon.co.uk/index.htm. You will also find quite a few schematics here, e.g. search for Krell.

Regards,

Eric

[capslock]

Originally posted by dkemppai
Hi,

I've been using the 1934 for a while. It seems to be a good part, but I do wish it was a little faster. I'm using it as a vas transistor, and have found it to be the slowest part in the amp.

If you locate a similar part that is faster, let me know... ...I'd be very interested.

-Dan

I guess you mean 1943? Why would you need this kind of power rating in the VAS stage? A TO-126 or TO-220 part will do nicely, even more so if you use it as a cascode transistor. There was a thread "choice of VAS transistor" a couple of days ago, have a look.

[pinkmouse]

Originally posted by capslock
Hi Al,

actually, bipolar output stages are the most common thing. As an exhaustive primer, have a look at: http://www.dself.demon.co.uk/index.htm. You will also find quite a few schematics here, e.g. search for Krell.

Thanks Eric, I am familiar with the idea of separate NPN and PNP output trannies, ( I can't say that I totally understand them yet!), but I was querying the use of bipolar transistors in one package, such as the OnSemi MJL1302A. Or am I getting the wrong end of the stick again!

[capslock]

Well, the MJL1302A has only three leads...

OnSem and Sanyo have the nice habit of issuing only one data sheet for a complentary pair.

Cheers,

Eric

[pinkmouse]

Thanks Eric, thats cleared it up for me, as per usual, my misreading of the data sheets is at fault

The three leads thing did make me think I was on the wrong track...

[dkemppai]

Originally posted by capslock


I guess you mean 1943? Why would you need this kind of power rating in the VAS stage? A TO-126 or TO-220 part will do nicely, even more so if you use it as a cascode transistor. There was a thread "choice of VAS transistor" a couple of days ago, have a look.

Yeah, I mean the 1943...

With Plus/Minus 100 volts maximum, I need bigger power ratings than a TO-92 or similar package can provide.

High levels of bias are needed to achieve high slew rates on the input of mosfet devices at high frequencies.

-Dan