Impossible FET or BJT design

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

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!