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Impossible FET or BJT design

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 | -15V

I 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.
 
M

mc

Jan 1, 1970
0
(See below)
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 | -15V

I 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,
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.

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,
Imagine a fixed resistor of, say, 1K to the -15V rail, and negligible
loading. Does that help?

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.
 
S

Spehro Pefhany

Jan 1, 1970
0
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 | -15V

I 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.

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
 
F

Fred Bloggs

Jan 1, 1970
0
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 | -15V

I have four power rails available: 0V, +5V, +15V and -15V.

I have racked my brain for an answer but have failed to find one.

Your truth table suggests an inverter and level translator. So something
like this:
View in a fixed-width font such
as Courier.
 
F

Fred Bloggs

Jan 1, 1970
0
Vin | Vout
0V | -10V
+3.3V | -15V

I have four power rails available: 0V, +5V, +15V and -15V.

More like this:
View in a fixed-width font such
as Courier.
 
P

Pooh Bear

Jan 1, 1970
0
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.

Why the need for fets ? This is a perfect application for an op-amp.

Graham
 
F

Fred Bloggs

Jan 1, 1970
0
This is probably even better:
View in a fixed-width font such
as Courier.
 
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.
 
P

Pooh Bear

Jan 1, 1970
0
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?

Ahem ! The *fet* ? How's the course been going ? Missed many lectures ?

Graham
 
P

Pooh Bear

Jan 1, 1970
0
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?

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.
 
P

Pooh Bear

Jan 1, 1970
0
Graham,

Fred is using ascii characters to map out a circuit.

I know !
Drawing the
proper symbol for the transistor is dificult.

There a few programs available to do this actually.
I can't tell from the ascii representation of the transistor if it is a JFET
or MOSFET.

It's neither. I was (a) pulling your leg and (b) trying to find out if you knew
what it really is.
The application involves switching power supplies to an IC. I don'twant to
use op-amps.

Whyever not ? Admittedly a transistor is cheaper though !

Graham
 
R

Rich Grise

Jan 1, 1970
0
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.

It's a PNP bipolar.

Good Luck!
Rich
 
R

Robert Baer

Jan 1, 1970
0
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.
Methinks that there is no FET inthe circuit given, so the answer is
"neither".
 
R

Robert Baer

Jan 1, 1970
0
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.
Don't know how to read a simple schematic?
 
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