15003/4 hfe

[effebi]

Today i finally decided to measure the static hfe of all my stock of TO3 cans MJ15003/4.
All my power transistor were bought in batches of about 50 over the time, only from mayor vendors (i.e. Farnell , etc.).
ALL are original Motorola/ON (Mex factory) , all never used in production.
I had about 120 BJTs to test, about half NPN and half PNP.
For the test, I had set a base current of about 3,5 mA , measuring the Ic on the 1 Ohm collector resistor. This gives usually 100-600 mA Ic, enough to make the transistors pretty warm with 10V collector supply. Measure was done always after 10 seconds of connection to the test circuit.
The results were quite surprisinng.

1) The old Motorolas had quite ALWAYS an hfe almost double than the modern ONsemi. Typical values of 220 for the -04 and 120 for the -03 for the Motorolas VS 150 for -04 and 60 for the -03 on the new ONsemi.
2)The -04 has CONSISTENTLY more than double the hfe than the -03 in the same batch. (batch is easily found because the transistor has the Year/Week prodution date on the case).
Inside the same batch the "variance" is quite low, around +-10%.

My conclusions:
1) You cant' assume that you can use any ONsemi transistor for repairing an amplifier using the old Motorolas, but you have to carefully select it.

2) When designing a circuit you cannot assume that the -04 is REALLY a complementary of the -03.

I would like to hear some opinion on the argument.
Thanks in advance
effebi

[lineup]

thanks for info
is a quite big difference

[infinia]

Interesting about the betas between MOT vs ON semi not sure what the conclusion is per the spec.
BTW I think the betas between PNP and NPN drops much closer as Ic max is approached ~ 8A,
Matching device betas on each rail (current sharing) is more important than PNP vs NPN where the driver beta differences also tend to equal them.

[effebi]

Current sharing is my main concern.
I have around in operation some amps with 10 pairs where some BJTs run noticeably hotter than the other ones, Emitter resistor notwithstanding.

BTW I have tested also other ab. 30 "used" devices, exactly the same results.
Good news: Only one "bad" new device, a 15004 with hfe = 18.

[infinia]

I think most amp repairs guys know its best to replace a whole rail at a time, I would feel comfortable plugging in a rail of new devices from same batch date without measured beta if Re was reasonably large > 0.3 ohms. esp since you are reporting 20% or better beta variation

[effebi]

Originally Posted by infinia

I think most amp repairs guys know its best to replace a whole rail at a time, I would feel comfortable plugging in a rail of new devices from same batch date without measured beta if Re was reasonably large > 0.3 ohms. esp since you are reporting 20% or better beta variation

That's right. I usually would do the same, with 2 exceptions:
1- you are on-site and time constrained.
2- Customers wants to "spare".....

[infinia]

well like everything
your time vs part costs vs reliability of repair job
pick any 2

[wg_ski]

Originally Posted by effebi

1) The old Motorolas had quite ALWAYS an hfe almost double than the modern ONsemi. Typical values of 220 for the -04 and 120 for the -03 for the Motorolas VS 150 for -04 and 60 for the -03 on the new ONsemi.
2)The -04 has CONSISTENTLY more than double the hfe than the -03 in the same batch. (batch is easily found because the transistor has the Year/Week prodution date on the case).
Inside the same batch the "variance" is quite low, around +-10%.
effebi

You may very well get the same variance between two old batches of Moto and two new batches of ON's. Nothing has really changed between Moto and ON - that kind of lot to lot variation is normal in power transistors. You'll probably find that Vbe at a given Ic is closer than the beta spread between the batches - and that's what really determines current sharing.

[AndrewT]

the devices must be at comparable temperatures to give comparable hFE.

You must test at constant Ic and constant Tc to get comparable hFE values.

[infinia]

Originally Posted by AndrewT

the devices must be at comparable temperatures to give comparable hFE.

You must test at constant Ic and constant Tc to get comparable hFE values.

Yes temp is important! If the OP measures same Ic and Vce @ 10 seconds would be acceptable.
BTW beta is a more accurate term here than hfe