Help needed with basic transistor assumptions

M

misterroy

Guest
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
 
"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.
Click to expand...
Too much detail for high-school students.

What are your basic objectives?

You have to compete with TV, peer pressure, roiling hormones and all of
that.
 
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.
Click to expand...
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
 
"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
Click to expand...
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
 
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.
Click to expand...
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
 
On Feb 13, 11:41 am, 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=dg57p3md_27hjs34bgc&revision=_latest

 Bear in mind we're working at a basic level, only using the
transistors as switches.

thanks
Click to expand...
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
 
On Feb 14, 4:55 am, Bill Bowden <wrongaddr...@att.net> wrote:
On Feb 13, 11:41 am, 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=dg57p3md_27hjs34bgc&revision=_latest

 Bear 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
Click to expand...
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.
 
On Feb 14, 4:55 am, Bill Bowden <wrongaddr...@att.net> wrote:
On Feb 13, 11:41 am, 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=dg57p3md_27hjs34bgc&revision=_latest

 Bear 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
Click to expand...
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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