I finally got the Vbe Matcher off of a Protoboard by moving it to Vectorboard.
It's been awhile since I did point-to-point Vectorboard.
The connections across the top are Power, 'Scope Monitor Out (filtered), Output to A/D, 1.5 mV P-P Calibration signal, 15V Trigger output.
The two jumpers and shunts switch the test socket from NPN to PNP.
There are two rows in the test socket.
The right-hand row is for CBE pinout transistors.
The left-hand row is for BCE pinouts.
The clip is to thermally equalize the test transistors.
A pair of BD139 BCE pinout transistors:
A 2SB737 pair:
One more project I can check off the list...
It's been a productive few weeks.
Transistor Vbe Matching Using A Commutating Chopper-Based Circuit
- mediatechnology
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- mediatechnology
- Posts: 5452
- Joined: Sat Aug 11, 2007 2:34 pm
- Location: Oak Cliff, Texas
- Contact:
Re: Transistor Vbe Matching Using A Commutating Chopper-Based Circuit
I added D1-D4 to clamp Ve.
Not only for the reason JR gives but also to reduce recovery time for when both devices are removed from the test socket.
Without D1-D4 Ve goes to the rail when Q1 and Q2 are removed.
- mediatechnology
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Re: Transistor Vbe Matching Using A Commutating Chopper-Based Circuit
I had used up my stock of matched ZTX-851 transistors for the flat MC preamp and the time had come to match some more up.
The ZTX851 for this run was from a different lot.
Out of 30 devices I had no problem getting 12 pairs matched to <1 mV which is adequate for the MC preamp.
This lot had higher gain, the average HFE was 185. The highest was 230.
Of the 6 transistors that wouldn't match 1 was bad (B-E short) so the yield is 24/29 or about 82%.
FWIW (knock on wood) I haven't found a noisy one yet out of about 120 devices.
The ZTX851 for this run was from a different lot.
Out of 30 devices I had no problem getting 12 pairs matched to <1 mV which is adequate for the MC preamp.
This lot had higher gain, the average HFE was 185. The highest was 230.
Of the 6 transistors that wouldn't match 1 was bad (B-E short) so the yield is 24/29 or about 82%.
FWIW (knock on wood) I haven't found a noisy one yet out of about 120 devices.