MJL4281-4302 Matching

[Chrisv1983]

I am building a P3A so I got some MJL4281s and some MJL4302s. I get good HFE matching between transistors of the same type (npn or pnp), but there is a quite big mismatch between PNPs and NPNs. Is this normal?

And the same thing happens with MJE15035 and 15034...

[Chrisv1983]

Does this happen with other complementary transistors?

And what would be sonic consequences of pnp-npn mismatching?

[Andypairo]

Matching devices becomes important when you need to parallel some of them to avoid current mismatches and so on, matching between different devices makes little sense to me (and to Rod also .

Even in the Alephs, where multiple mosfets are used in parallel, it is suggested to match only the devices that will be connected that way.

Cheers

Andrea

[AKSA]

There are always large differences in Vbe between NPN and PNP. This is quite normal, and makes little difference in practice.

However, as Andrea comments, if you parallel a number of NPN devices (or PNP devices) then like devices should be matched.

This matching must be done for both Vbe (most important) and beta (less important).

Vbe should be matched within 1mV at the same ambient temperature, and for a current through the device which closely matches the bias current which will be used in the amplifier.

Beta should also measured at the bias current, and should be matched within about 5%. 0R33 emitter resistors (or higher) will ensure that current sharing is almost identical.

Cheers,

Hugh

[MrTransistorm]

I just noticed the same thing with my MJL21193/21194 transistors. At an Ic of both 50mA and 100mA the hfe of the NPN's were around 50 while the PNP's were over 100!

A quick look at the datasheet tells all. For mine, at lower currents the PNP devices clearly have much higher hfe than the NPN's. They start to even out around 1A, but they still don't look like very good complimentary devices. Hmmmm, I wish I had studied the specs a little more before I ordered them. Oh well, they'll do fine until I can get some MJL4281A/4302A's

OK, the point is: don't worry about matching the NPN's to the PNP's. As long as your driver stages are capable of supplying enough drive current, the the actual hfe value is not too important. Just match the LIKE devices and you'll be fine.

[jackinnj]

note that in the PDF for the MJL21193/4 On Semi specifies the THD for matched HFE at 0.08% vs 0.80% unmatched.

jack

[Eva]

Matching the beta between NPN and PNP output devices is useless except when the drivers and pre-drivers are also matched

Actually, the values to match are beta_predriver*beta_driver*beta_out between high and low sides, this is in order to make both sides have the same *total* current gain [as seen by the VAS] and reduce THD and crossover distortion

Particular gain of each device is not important at all since there are different devices in series

Matching the betas of the output devices of the same polarity is useless since it has little efect over current sharing