Multi-collector/emitter BJTs

[vishwa]

Hi,
Is there a commerical BJT part for modeling multi-collector and/or
multi-emitter BJTs in spice? Or could I model them just by using two
individual BJTs?

thanks!
vishwa

 

[Jim Thompson]

On 4 Jun 2004 10:39:44 -0700, vishwa_23@yahoo.com (vishwa) wrote:

Hi,
Is there a commerical BJT part for modeling multi-collector and/or
multi-emitter BJTs in spice? Or could I model them just by using two
individual BJTs?

thanks!
vishwa

For multi-emitter situations there is no issue and a
multiple-transistor model will work just fine.

For multi-collector devices some caution is required if saturation of
one collector occurs... you need to add interaction to the model using
a subcircuit format.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Kevin Aylward]

Jim Thompson wrote:

On 4 Jun 2004 10:39:44 -0700, vishwa_23@yahoo.com (vishwa) wrote:

Hi,
Is there a commerical BJT part for modeling multi-collector and/or
multi-emitter BJTs in spice? Or could I model them just by using two
individual BJTs?

thanks!
vishwa

For multi-emitter situations there is no issue and a
multiple-transistor model will work just fine.

For multi-collector devices some caution is required if saturation of
one collector occurs... you need to add interaction to the model using
a subcircuit format.

Or realise that if one saturates, your circuit, in all likelihood, aint
going to work, so don't do it. If you don't do it, you don't need a
better model.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[vishwa]

Hi,
er..there is still some doubt in my mind..for multi-emitter
transistors, do i just 'join' the collectors and bases of two BJTs? on
similar lines, would it work if I just 'joined' the emitters and bases
of the two BJTs?
i have never done this before, and hence these doubts...also, what
would be a good check to see if the model saturates..by measuring Vce?

thanks!
vishwa

"Kevin Aylward" <kevin.aylwardEXTRACT@anasoft.co.uk> wrote in message news:<qc6wc.10986$wd7.8599@front-1.news.blueyonder.co.uk>...

Jim Thompson wrote:
On 4 Jun 2004 10:39:44 -0700, vishwa_23@yahoo.com (vishwa) wrote:

Hi,
Is there a commerical BJT part for modeling multi-collector and/or
multi-emitter BJTs in spice? Or could I model them just by using two
individual BJTs?

thanks!
vishwa

For multi-emitter situations there is no issue and a
multiple-transistor model will work just fine.

For multi-collector devices some caution is required if saturation of
one collector occurs... you need to add interaction to the model using
a subcircuit format.

Or realise that if one saturates, your circuit, in all likelihood, aint
going to work, so don't do it. If you don't do it, you don't need a
better model.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Robert Baer]

vishwa wrote:

Hi,
er..there is still some doubt in my mind..for multi-emitter
transistors, do i just 'join' the collectors and bases of two BJTs? on
similar lines, would it work if I just 'joined' the emitters and bases
of the two BJTs?
i have never done this before, and hence these doubts...also, what
would be a good check to see if the model saturates..by measuring Vce?

thanks!
vishwa

"Kevin Aylward" <kevin.aylwardEXTRACT@anasoft.co.uk> wrote in message news:<qc6wc.10986$wd7.8599@front-1.news.blueyonder.co.uk>...
Jim Thompson wrote:
On 4 Jun 2004 10:39:44 -0700, vishwa_23@yahoo.com (vishwa) wrote:

Hi,
Is there a commerical BJT part for modeling multi-collector and/or
multi-emitter BJTs in spice? Or could I model them just by using two
individual BJTs?

thanks!
vishwa

For multi-emitter situations there is no issue and a
multiple-transistor model will work just fine.

For multi-collector devices some caution is required if saturation of
one collector occurs... you need to add interaction to the model using
a subcircuit format.

Or realise that if one saturates, your circuit, in all likelihood, aint
going to work, so don't do it. If you don't do it, you don't need a
better model.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

If you are going to physically combine de=iscretes, then i suggest you
match the Vbe (all measured at desired operating current) within a few
millivolts; a mismatch of about 2.5mV will create an Ie ratio of 1.10 .