BetaDC versus IC with LTSpice

H

honest

Guest
I want to simulate the dependence of BetaDC on the current collector
bias current for a 2N3904, by using LTSpice.

So I used a fixed VCE (5V) using a constant voltage source
and a DC current source Ib applied at the base.

Then I performed a DC analysis simulation in which the sweep variable
is the current source Ib and plotted the quantity:

Ic(q1) / Ib(q1)

versus Ic

The results are wrong:

<http://img14.imageshack.us/img14/8614/curvebetadc.gif> [136 kB]

Where I am mistaking?
Thanks in advance.


CURVEBETAdc.ASC

Version 4
SHEET 1 2472 1528
WIRE 2128 1152 1984 1152
WIRE 1984 1200 1984 1152
WIRE 2128 1216 2128 1152
WIRE 1920 1248 1840 1248
WIRE 1840 1264 1840 1248
WIRE 1840 1360 1840 1344
WIRE 1984 1360 1984 1296
WIRE 2128 1360 2128 1296
FLAG 2128 1360 0
FLAG 1984 1360 0
FLAG 1840 1360 0
SYMBOL npn 1920 1200 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL voltage 2128 1200 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName VC
SYMATTR Value 5
SYMBOL current 1840 1344 M180
WINDOW 0 23 79 Left 0
WINDOW 3 24 0 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName IB
SYMATTR Value 10ľ
TEXT 1806 1384 Left 0 !.dc IB 0 50u .05u
 
On Fri, 06 Nov 2009 20:25:49 +0100, honest <none@host.com> wrote:

I want to simulate the dependence of BetaDC on the current collector
bias current for a 2N3904, by using LTSpice.

So I used a fixed VCE (5V) using a constant voltage source
and a DC current source Ib applied at the base.

Then I performed a DC analysis simulation in which the sweep variable
is the current source Ib and plotted the quantity:

Ic(q1) / Ib(q1)

versus Ic

The results are wrong:

http://img14.imageshack.us/img14/8614/curvebetadc.gif> [136 kB]

Where I am mistaking?
Thanks in advance.


CURVEBETAdc.ASC

Version 4
SHEET 1 2472 1528
WIRE 2128 1152 1984 1152
WIRE 1984 1200 1984 1152
WIRE 2128 1216 2128 1152
WIRE 1920 1248 1840 1248
WIRE 1840 1264 1840 1248
WIRE 1840 1360 1840 1344
WIRE 1984 1360 1984 1296
WIRE 2128 1360 2128 1296
FLAG 2128 1360 0
FLAG 1984 1360 0
FLAG 1840 1360 0
SYMBOL npn 1920 1200 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL voltage 2128 1200 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName VC
SYMATTR Value 5
SYMBOL current 1840 1344 M180
WINDOW 0 23 79 Left 0
WINDOW 3 24 0 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName IB
SYMATTR Value 10ľ
TEXT 1806 1384 Left 0 !.dc IB 0 50u .05u
Click to expand...
Start with some non-zero value of IB. You're just getting classic 0/0
problems.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama says, "I AM NOT a cry baby, Fox REALLY IS out to get me!"
 
On Fri, 06 Nov 2009 21:40:58 +0100, honest <none@host.com> wrote:

Jim Thompson ha scritto:

Start with some non-zero value of IB. You're just getting classic 0/0
problems.

Starting with IB=.1u now works.
Thanks!
Click to expand...
You're welcome! BTDT ;-)

For your amusement, throw an ideal feedback loop from
collector-to-base, such that it holds VCE at some value of your
choice, say 1V; then force IC.

You'll then be able to observe the overall behavior of BF, IKF and
ISE, versus IC.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 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.
 
Jim Thompson ha scritto:

Start with some non-zero value of IB. You're just getting classic 0/0
problems.
Click to expand...
Starting with IB=.1u now works.
Thanks!
 
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