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Sci.Electronics.Basics -> Help needed with basic transistor assumptions
There are 8 messages in this thread.
You are currently looking at messages 1 to 8.
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Author: misterroyDate: 14:41 13-02-08
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Author: CharlesDate: 17:34 13-02-08
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Author: John PopelishDate: 17:55 13-02-08
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misterroy wrote:
> Hi, I'm a high school teacher and I've been working on a transistor
> revision sheet for my students. I'd appreciate any comments on the
> sheet I have made. Its at:
>
> http://docs.google.com/View?docID=dg57p3md_27hjs34bgc&revision=_latest
>
> Bear in mind we're working at a basic level, only using the
> transistors as switches.
My first impression was that your voltage arrows looked like
current indications. Current has a direction through
something. Voltage is a difference between two nodes. A
line with a plus at one end and a minus at the other with a
circle in the middle of the line with Vbe or some other
label in the circle is a more standard way to show voltage
difference between pairs of nodes. Arrow along side of a
path is a normally used as a current indication.
By the way a transistor in the thermistor circuit shown
(thermistor voltage divider amplifier) will behave very far
from a switch, except for very large temperature changes.
--
Regards,
John Popelish
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Author: Bob MonsenDate: 18:43 13-02-08
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"misterroy" <rgdavidson@gmail.com> wrote in message
news:208d65d7-bd20-49ee-a535-d92e67a26965@u10g2000prn.googlegroups.com...
> Hi, I'm a high school teacher and I've been working on a transistor
> revision sheet for my students. I'd appreciate any comments on the
> sheet I have made. Its at:
>
> http://docs.google.com/View?docID=dg57p3md_27hjs34bgc&revision=_latest
>
> Bear in mind we're working at a basic level, only using the
> transistors as switches.
>
> thanks
Very nice presentation.
One small suggestion is that I'd explain what each thing is before
describing how it is used in the circuit. I'd also give a simple formula or
maybe even a text rule for them to use to predict how differences will
change the effect. I'd also arrange things so that each device and concept
is explained before it is used.
As John says, the voltage arrows should go. I always think of voltage as a
distance, and current as a vector. So, I'd use the sorts of legends that one
would use to describe a distance on a drawing for the voltage between ground
and Vb, for example, perhaps with arrows on both sides.
Regards,
Bob Monsen
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Author: Rich GriseDate: 21:01 13-02-08
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On Wed, 13 Feb 2008 11:41:54 -0800, misterroy wrote:
> Hi, I'm a high school teacher and I've been working on a transistor
> revision sheet for my students. I'd appreciate any comments on the sheet I
> have made. Its at:
>
> http://docs.google.com/View?docID=dg57p3md_27hjs34bgc&revision=_latest
>
> Bear in mind we're working at a basic level, only using the
> transistors as switches.
>
It's awful. You don't connect a thermistor to a switch. You need some
kind of threshold, and an actual switch. To improve the circuit, replace
the relay with a milliammeter (maybe with a series resistor) to
demonstrate the transfer function in the linear region.
To do a switch, just use a switch for input, and you can demonstrate
inversion.
To do them both, combine the above and put in some feedback to make
it a Schmitt trigger.
Have Fun!
Rich
Good Luck!
Rich
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Author: Bill BowdenDate: 23:55 13-02-08
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On Feb 13, 11:41=A0am, misterroy <rgdavid...@gmail.com> wrote:
> Hi, I'm a high school teacher and I've been working on a transistor
> revision sheet for my students. I'd appreciate any comments on the
> sheet I have made. Its at:
>
> http://docs.google.com/View?docID=3Ddg57p3md_27hjs34bgc&revision=3D_latest=
>
> =A0Bear in mind we're working at a basic level, only using the
> transistors as switches.
>
> thanks
Looks pretty good. One comment on the MOSFET operation is the current
into the gate is not exactly zero and may be quite high depending on
the frequency of operation. There is a capacitance from gate to source
that needs to be charged (or discharged) every time the mosfet is
switched on or off. The more frequently you do this will increase the
average current required.
-Bill
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Author: misterroyDate: 02:14 14-02-08
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On Feb 14, 4:55=A0am, Bill Bowden <wrongaddr...@att.net> wrote:
> On Feb 13, 11:41=A0am, misterroy <rgdavid...@gmail.com> wrote:
>
> > Hi, I'm a high school teacher and I've been working on a transistor
> > revision sheet for my students. I'd appreciate any comments on the
> > sheet I have made. Its at:
>
> >http://docs.google.com/View?docID=3Ddg57p3md_27hjs34bgc&revision=3D_lates=
t
>
> > =A0Bear in mind we're working at a basic level, only using the
> > transistors as switches.
>
> > thanks
>
> Looks pretty good. One comment on the MOSFET operation is the current
> into the gate is not exactly zero and may be quite high depending on
> the frequency of operation. There is a capacitance from gate to source
> that needs to be charged (or discharged) every time the mosfet is
> switched on or off. The more frequently you do this will increase the
> average current required.
>
> -Bill
The voltage arrows may be a transatlantic thing, I'm in the UK and
they are pretty standard here. I am aware of how poor a switch the
thermistor circuit gives, the graphic at the top with the thermistor
comes from a government produced exam paper. The course does not take
into account frequency effects so the FET should be ok too.
thanks for taking the time to read over my work.
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Author: misterroyDate: 02:20 14-02-08
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On Feb 14, 4:55=A0am, Bill Bowden <wrongaddr...@att.net> wrote:
> On Feb 13, 11:41=A0am, misterroy <rgdavid...@gmail.com> wrote:
>
> > Hi, I'm a high school teacher and I've been working on a transistor
> > revision sheet for my students. I'd appreciate any comments on the
> > sheet I have made. Its at:
>
> >http://docs.google.com/View?docID=3Ddg57p3md_27hjs34bgc&revision=3D_lates=
t
>
> > =A0Bear in mind we're working at a basic level, only using the
> > transistors as switches.
>
> > thanks
>
> Looks pretty good. One comment on the MOSFET operation is the current
> into the gate is not exactly zero and may be quite high depending on
> the frequency of operation. There is a capacitance from gate to source
> that needs to be charged (or discharged) every time the mosfet is
> switched on or off. The more frequently you do this will increase the
> average current required.
>
> -Bill
The voltage arrows may be a transatlantic thing, I'm in the UK and
they are pretty standard here. I am aware of how poor a switch the
thermistor circuit gives, the graphic at the top with the thermistor
comes from a government produced exam paper. The course does not take
into account frequency effects so the FET should be ok too.
thanks for taking the time to read over my work.
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