Matching transistors - Measuring hfe

[TomWaits]

I received 100 pcs each of On Semi MPSA42 & MPSA92. I measured the hfe of the devices using a Mastech MS8230B. I also had some older National Semi MPSA42’s so I tested them too. I’m not certain of the exact circuit this digital meter uses internally for this test but here are the results. My obvious purpose was to match NPN and PNP pairs but the results were not as good as I expected.

I am very interested in hearing your comments as this is the first time I have done this type of measurement.

Cheers,

Shawn.

On Semi MPSA92 PNP

hfe - QTY
120 - 2
118 - 3
117 - 5
116 - 5
115 - 2
114 - 3
112 - 9
111 - 11
110 - 8
109 - 24
108 - 13
107 - 12
105 - 2

On Semi MPSA42 NPN
Hfe - QTY
101 - 5
97 - 6
95 - 13
94 - 2
93 - 12
92 - 17
91 - 7
90 - 5
89 - 12
87 - 6
85 - 4
65 - 2
64 - 1
53 - 2
48 - 1
47 - 1
46 - 1
38 - 1
35 - 1

National Semi MPSA42
hfe - QTY
274 - 1
252 - 1
246 - 1
226 - 1
129 - 1
114 - 1
97 - 1
87 - 1
85 - 1
74 - 1
57 - 1
56 - 1
50 - 1
47 - 1

[jackinnj]

you have demonstrated the reason for which National Semi no longer sells discretes.

fwiw -- i often see a bimodal distribution of hfe, vbe for BJT's and vgs for Lateral and vertical MOSFETs.

[TomWaits]

Originally posted by jackinnj
you have demonstrated the reason for which National Semi no longer sells discretes.

fwiw -- i often see a bimodal distribution of hfe, vbe for BJT's and vgs for Lateral and vertical MOSFETs.

Jack, that is funny and could you explain bimodal?

[TomWaits]

I didn't stop there as I ordered 15 pcs each of On Semi MJE15032
& MJE15033. The results:

MJE15032_ _MJE15033
hfe - qty _ _ _hfe - qty
119 - 1_ _ _ _139 - 5
112 - 1_ _ _ _138 - 4
109 - 1_ _ _ _137 - 6
104 - 1
99 - 1
80 - 2
79 - 2
78 - 1
77 - 3
76 - 2

So when you match bipolars, if you do match them at all, do you use hfe in the selection process? Do you pair them as close as you can? Or do you match them for exact specs? Do you buy your semiconductors by the thousands when you only need 10?

It's new to me, I like the concept but geez this could be expensive to go all out 100% everytime?

Your thoughts and opinions are appreciated.

Shawn.

Edit: Better looking table.

[jackinnj]

Originally posted by TomWaits


Jack, that is funny and could you explain bimodal?

two humps

[TomWaits]

Originally posted by jackinnj


two humps

I'm lucky if I get one a week.
What about the two hfe humps? The five W's...lay them on me Jack 'cause I know Jack.

Shawn.

[TomWaits]

This is a poor way of measuring hfe?

Shawn.

[TomWaits]

So the hfe of the PNP does not have to match the hfe of it's complimentary NPN? Is this true?

Shawn.

[lineup]

Originally posted by TomWaits

So the hfe of the PNP does not have to match the hfe of it's complimentary NPN? Is this true?

Shawn.

It is not often we can get a perfect match of any NPN PNP.

In a symmetrical input pair,you can match Vbe, for minimum offsets due to Vbe differences.
When you do this, you usually end up with different HFE for the npn/pnp.

This means you get input bias current offset
as the gain is different, and so one pair will need more base current for same collector current.

There are 2 ways to compensate for this bias current offset.
1. Keep the same collector currents in both pairs.
And provide a cancelling little current to the input.

2. Change the current in one pair, until the the base currents are the same.
This will also give ZERO current in input resistor = no offset.


Now also when matching NPN to NPN in a pair
you may end up with different HFE in these 2 transistors,
if you have matched for Vbe.
--------------------

This can happen especially if your transistors are NOT from same BATCH.
This is why it is good to buy for example 100 small signal transistors
in one package, and so try to make sure,
they were made from the same silicon substrate
on the same day and by the same machine!

What will determine the quality of a transistor
is the quality and pureness of the raw material used.
Like with diamond and pearls ... there can be imperfections in the pearl.
Same with the silicon mineral sheets that are used for semiconductors.

When you order you can even ask if you can get all your BC550C from the same original package.
If your supplier can do this, it is good.

Of course this goes for Power Devices, too.
There is a better chance they have similar parameters
if they come from same production unit in a specific day.


Buying a few transistors here and a few there and in different years/months
and maybe even from different brands, manufacturers,
will make it more different to find 2 good matching BC550C.


Regards
lineup

[lineup]

When you buy for example BD139
you can try to find transistors that are sorted.

I think BD139 can be found in these 3 classes
order by HFE:
BD139-10 gain 63-160
BD139-16 gain 100-250
BD139-25 gain 160-400
10 means average gain ~100
16 means average ~160

And if you buy one marked only BD139 it is unsorted.
And the variations can be maximal: 63-400

Compare this to BC547, BC547A, BC547B, BC547C
One BC547, unsorted, can have a gain of 110-800.

It is not like that, that the manufacturer decide:

- Now we will make some BC547C from this silicon piece.

No!
They take the silicon sheet and start making small signal transistors.
Then they check the result and the data of the finished transistors.
If they match the 'BC547C specifications' .. they label them BC547C
Other transistors will have lower hFE and so they are labelled BC547A

It comes from the quality of silicon material used.
What the resulting transistor will be called.
And each marked, labelled transistor
should match the datasheet specifications and tolerances for it.
When it comes to parameters.


lineup
Lineup Audio Transistor Lab