OT: SOT-523 PNP Question

Sure, and that helps the tracking a lot, but it also loses the advantage in output swing that Tim was talking about.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
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hobbs at electrooptical dot net 
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Reply to
Phil Hobbs
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it depends on the axis you use to flip it.

rotate 180 degrees about the line from pin 1 centre through the centre between pins 2 and 3,

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Reply to
Jasen Betts

Because they're bigger devices, silly. The BCV62 has a specified theta_JA of 500 K/W. Given a theta number, it's really easy to calculate the thermal stability limit analytically.

Nah, I use them a fair amount, but only down below 500 uA. They're also useful for making temperature compensated current sources, for instance--think of the diode-connected device as a way of temperature compensating the V_BE of the current source device.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

It would have to be upside down and rotated. It actually does fit well enough that you don't need bits of wire -- but on the parts we had you couldn't reform the leads without them breaking off, so it's a highly questionable thing to do with a production board. We just did it to verify the rest of the board before giving the layout a hard time and doing it over.

Your adapter board idea is probably better, if they fit, or your rotate- and-wire idea. It's a hell of a lot of work, though.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

Try it some time... in CMOS it can actually _improve_ the swing range before the current decreases (patent pending :) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
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Reply to
Jim Thompson

I don't read that set of curves (strange as they are) as implying run-away. When I have a moment I'll run some numbers. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

I determined that the transistor wasn't needed, it was overkill, so suck off transistor, replace with a resistor... lots of labor but, fortunately, it's on main-land China. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

'Tain't hard to calculate. At constant V_BE, a junction temperature rise of 1 degree produces a current increase of 9%. Assuming a low-Z collector load, device dissipation increases by 9% as well. Instability will occur if that 9% causes a temperature change of another degree, i.e.

0.09 I_C V_CE theta_JA > 1 K.

The general derivation isn't much harder, even with a more complicated load.

If you bias the output transistor near its maximum-power point, you can even use this effect as a temperature controller:

formatting link

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Sure, but BSS84s are 4c/ea in 1000s, versus MMBT3906s for 2.2c. And they probably aren't as well matched. Actually, I haven't compared FETs on tape... hmm...

Tim

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Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

Yup -- still fine when a wimp is all you need. And in the grander scheme of things, 0.5mA is hardly useless.

Any clue how the Rth(j-j) is between them? Twin packs are notoriously weak, but I wonder if having common metal makes them any better, even if it's two bond wires.

Tim

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Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

OK, for that you need to charge a fee.

$0.xx for chalking a mark on a pipe. $XXX,XXX.xx for knowing where to make a chalk mark on a pipe...

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

I have some germanium transistors which act like really slow latches. Once turned on, they bias themselves at half supply voltage, go figure!

Tim

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Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

GE built some radios and phono amps with crap like that in the '60. No bias resistors, just the internal leakage. Probably fallout from the military & commercial product lines.

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Reply to
Michael A. Terrell

In the classic low-level audio amp stage bias scheme (divider to bias up the base, resistor in the source) the base divider often took current *out* of the base!

One occasionally saw an amp circuit with the base of a Ge transistor driven through a cap... and nothing else.

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John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
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Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
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Reply to
John Larkin

The Infineon ones seem to be a bit better--they claim somewhat higher maximum dissipation before instability.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

The synchronized-runaway trick can be used to enable multiple transistor array chips to be used much like a single larger array. That's potentially quite useful in my business.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

I believe that. CMOS tends to be crappy that way, but OTOH you can bandage it with a whole lot of auxiliary transistors.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

Theta_JA isn't the pertinent number, it's Theta_JC (junction to case), or even more accurately junction-to-mounting-slug. What did you get you PhD in... exaggeration ?>:-}

More in a couple of days... off to Yuma to the inauguration of the son-in-law. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Yep, that's the (golden) rule >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

The best of all worlds is BiCMOS. But CMOS isn't "crappy"... if you know how to design with it. With my proprietary cascode I can easily get to 0.2V of rail before it sags. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

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