Hi,
I wonder could anyone devise a simple switching circuit using FET's of BJT's for the following truth table:
Vin | Vout 0V | -10V
+3.3V | -15VI have four power rails available: 0V, +5V, +15V and -15V.
I have racked my brain for an answer but have failed to find one.
Thanks in advance.
Ross.
Let me suggest a subproblem: Obtaining a -10V power rail. Work on getting -10V first.
You haven't said how much output current is required.
Thanks for the reply mc,
I can get the -10V power rail using a potential divider between the
-15V and 0V rails.
The output current required is 100uA.
Ross.
Thanks for the reply Spehro,
Maybe I'm missing what you are suggesting here but this doesn't seem to help. I want a switching circuit which when 0V is applied to the input, -10V will appear at the output. Similarly, when 3.3V is applied at the input, -15V will appear at the output.
Ross.
Assuming this is a homework question...
Imagine a fixed resistor of, say, 1K to the -15V rail, and negligible loading. Does that help?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Your truth table suggests an inverter and level translator. So something like this: View in a fixed-width font such as Courier.
. . . +5V . | . [1k] . | . +-----. . | | . [2k] | . | | . --- | . 0V | . | . | . .-----' . | . |< . in>------| . |\\ . | . | . [10k] . | . +------> out . | . [20k] . | . | . --- . -15V . .
More like this: View in a fixed-width font such as Courier.
. . +5V . | . [1k] . | . +-----. . | | . [2k] | . | | . --- | . 0V | . | . | . .-----' . | . |< . in>------| . |\\ . | . | . [20k] . | . +------> out . | . [10k] . | . | . --- . -15V . .
Why the need for fets ? This is a perfect application for an op-amp.
Graham
You sure like to give orders...pity your students.
This is probably even better: View in a fixed-width font such as Courier.
. . +5V . | . [2k] . | . +-----. . | | . [1k] | . | | . --- | . 0V | . | . | . .-----' . | . |< . in>------| . |\\ . | . | . [20k] . | . +------> out . | . [10k] . | . | . --- . -15V . .
Thanks for the reply Fred,
Is the FET an n-channel or p-channel? Is the drain connected to the upper part of the schematic or the lower part?
Ross.
Ahem ! The *fet* ? How's the course been going ? Missed many lectures ?
Graham
Jfet or mosfet btw ?
Graham
Graham,
Fred is using ascii characters to map out a circuit. Drawing the proper symbol for the transistor is dificult. I can't tell from the ascii representation of the transistor if it is a JFET or MOSFET.
The application involves switching power supplies to an IC. I don't want to use op-amps.
Ross.
I know !
There a few programs available to do this actually.
It's neither. I was (a) pulling your leg and (b) trying to find out if you knew what it really is.
Whyever not ? Admittedly a transistor is cheaper though !
Graham
It's a PNP bipolar.
Good Luck! Rich
Methinks that there is no FET inthe circuit given, so the answer is "neither".
Vacuum FET, as in tube.
Don't know how to read a simple schematic?
Bipolar syndrome! Get that medication to it NOW!
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