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OT: SOT-523 PNP Question

A technician in Auckland, NZ. ...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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;)

Mirrors are pretty interesting, though--the switcheroo Wilson mirror below has three, count 'em, three feedback loops. Also the usual trick of emitter degenerating Q3 and Q4 to improve matching also trashes the main loop bandwidth.

I_in I_out

0 | 0 | V | | | | | *---------* | | | | | Q1 | Q2 | \ | / \| | |/ |-------*------| V| |V / \ | | | *---------* | | | | Q3 | Q4 | \ | / \| | |/ |-------*------| V| |V / \ | | | | *----------*---------* | GND

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

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

What's good, compliance or accuracy? If you're looking for the latter, you probably are better off with a dumb resistor, or something active to mirror the current more precisely than transistors can anyway. If you need compliance but don't care if it's off by a factor of two, go right ahead; best part about discrete is you don't even have to worry about lateral PNPs.

Nice thing about current mirrors (with little or no degeneration), they saturate very near the rail. A one-Vbe-emitter-drop type can't pull that.

Tim

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

At sufficiently low current, I agree. At higher current, especially with small devices, the output device will run away because the thermal coupling isn't good enough to make the V_BEs track. For instance, Figure 13 of the BCV62 datasheet is worth thinking about--it shows the output device running away at only 15 mW of dissipation. Monolithics are much better.

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

Figs 14 and 15 make no sense. There's no base current for TR1.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

But it looks so much nicer without that ugly line right across the bottom. ;)

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

People who call a transistor TR deserve to have them not work.

Here's an NEC dual transistor with, as I recall, 50 mW dissipated on one chip.

formatting link

Not very isothermal.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

You _can_ cascode discretes just like you do monolithically.

Here's a past comparison of current mirror types...

...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

Some "artist" in the datasheet department left off the common ground from both drawings. When I was at Motorola I had many problems making sure that datasheets that went out the door were accurate. ...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

You may as well include an opamp and get some serious accuracy and temperature stability, and an easily programmable mirror ratio. Four parts, or even three if you get a little tricky.

Does anybody make an integrated opamp-based current mirror?

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

I have many... on custom chips... but it doesn't take an OpAmp to do it, just a diff-pair in CMOS is quite sufficient.

But, in most cases, CMOS doesn't need such frivolity, current mirrors can be made quite accurately with cascoded devices. ...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

Other than type "BARE", none of these have significant temperature effects when implemented monolithically...

And even "BARE" isn't too bad. ...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

So why don't mine at over 20mA and 10V? :)

Rth(j-a) = 500 K/W is a bit unfair relative to a TO-92 in still air (~100C/W), but it's the difference that matters. With Rth(j-j) large (they're adjacent, but not bonded... probably in the 1000s C/W), it shouldn't take much. No, not tested beyond 40C or so.

Besides the funny drawings, it also doesn't specify if this is maximum over temperature, or just at room temperature. The former would seem more reasonable. There's no corresponding datapoint in the tables to compare to, where conditions might be listed.

Also, what happened to their hFE plots?

As for changing my opinion of discrete current mirrors, this datasheet has only convinced me to never buy BCV62s. :o)

Tim

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

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

--
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 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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For a good time: install ntp 

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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    | 
| 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 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

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