What's the magic of 2N5551 / 2N5401?

[Mark Johnson]

The Locky-Z curve tracer's Hfe -vs- Icollector function is a little wonky at very low currents, and unfortunately a high-Beta PNP has extremely low base current when Icollector is less than a milliamp. So the far left edge of the attached plot, is not terribly trustworthy. Rb=91K was selected so that I could plot all the way out to 25mA of collector current. Measurements were taken this morning.

_

 

[jxdking]

Found @Mark Johnson 's old thread.

Thread 'Measuring the Early voltage "VA" of some PNPs at 8mA'

2016-10-24 12:45 am

I'm building current sources and current mirrors that run at about 8mA of bias, and trying to decide which device types to select. Among the criteria I have considered, is the Early Voltage (SPICE parameter "VAF"), which determines the output conductance, the "flatness" of the Ice vs Vce curves.

I plopped a bunch of PNP thru-hole transistors on the curve tracer and found to my surprise, that they didn't match up to the Early voltage measurements in The Art Of Electronics 3rd Edition, Table 8.1a, page 501.

Here's a spreadsheet showing my measured values, in the vicinity of 8 milliamps...

• Mark Johnson

• 

In this context (early voltage), KSC1845/KSA992 are not bad at all.

 

[Mark Tillotson]

KSA992
that is the reason why.... after 1mA you just get less then 500hfe....

View attachment 1438129

Yes, but most uses are 2 to 6mA, hardly falling off a cliff at that range - run one at 10mA from 50V rails and it will run too hot anyway so the gain droop isn't really a limiting factor in practice.

 

[Mark Johnson]

Beta = 1600 at 1mA , rises very slightly as Ic increases to 10mA. Caution: it's SMD and NPN. (link)

In stock at mouser.com, price = $0.61

 

[Carm2K]

What about the SMD ones.? 120V
You would need adaptors but they look really good.👍
Toshiba
2SC2713 2SA1163
2SC3324 2SA1312
2SC4117 SA1587

 

[chermann]

second line is not available at mouser or digikey but yes..they are fine. just 100mW and is good for LTP or CCS with 1-3mA

kr
Chris

 

[chermann]

2SC4117 - SA1587 are in SC-70 - 3 housing (3 pins) at mouser
SOT-23 is bigger

 

[chermann]

if you want to save space SSOT 6 - but you have to match - use FMB551
or with SOT23-3 MMBT5551

 

[Carm2K]

Those Toshiba ones are very close to their SC2240BL -SA970BL.
The hFE is flat up to 30mA.
Even the GR ones are 200 - 400.
Ive got KTC3400GB - KTA2400GC in mine. IPS. hFE 250. Those are all within spec.
Others are KTA1268BL KTC3198Y KTC3200BL KTA1024Y KTC3206Y KTA1266Y
Im looking at equivalents. Had me looking at all the different ones. The KTA1268BL's have gone down a lot. In the 300's.
I'd love to see them all on a Curve Tracer but missed out on one.🙁

 

[Carm2K]

Diodes Inc
FMMT497 - FMMT597 300V
Arcam used them in their Amplifiers.