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:
Bear in mind we're working at a basic level, only using the transistors as switches.
thanks
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.
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
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
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
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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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.
t
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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