[sdiy] Matched transistors - critical parameters?

Tom Wiltshire tom at electricdruid.net
Thu Feb 9 16:56:56 CET 2012

On 9 Feb 2012, at 07:46, Dave Manley wrote:

> On 2/8/2012 11:17 AM, ASSI wrote:
>> On Wednesday 08 February 2012, 09:05:50, Matthew Smith wrote:
>>> The DMMT5551 (and DMMT5401 for PNP) from Diodes Inc., are "intrinsically
>>> matched," which is explained as being built on adjacent dies from a
>>> single wafer.
>> This might be a marketing term for "we have no reason to believe otherwise,
>> but we don't bother to actually measure it".  Check the datasheet for what
>> they _guarantee_ for the matching (I'd be very surprised if Vbe matching was
>> guaranteed to be better than about 10mV, for instance).  Actual measurements
>> of matching properties are rather expensive since they take time.
> http://www.diodes.com/datasheets/ds30436.pdf:
> "8.   The DC Current Gain, hFE, (matched at IC = 10mA and VCE = 5V) Collector
> Emitter Saturation Voltage, VCE(SAT), and Base Emitter Saturation Voltage,
> VBE(SAT) are matched with typical matched tolerances of 1% and maximum of 2%."

Is that good or not? I'm not familiar with the standards that are expected of matched transistors, so I'd like to know if that represents a decent level of matching, a good level, or a poor level.

I'm guessing that you wouldn't do much better by hand, unless you got really autistic about it.


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