depletion mode pmos for ultra simple logic level translation

[Simon S Aysdie]

Does it exist? Would it work? Could it be extremely cheap? Does
anyone make a "small" surface mount pmos depletion device at all?

Vgs_off of "regular" JFET parts like a MMBFJ271 go up to 4.5 V, which
is too high. Or for J270, the min I_DSS is too low.



-
--- GND
-----
|
|
|S-+
<0,3.3>V O------G||
|D-+
|
+------O <-5,0> V
|
\
/
\ 1k
/
|
|
~ -5V

 

[Gary Reichlinger]

Does it exist? Would it work? Could it be extremely cheap? Does
anyone make a "small" surface mount pmos depletion device at all?

Supertex may have something like that.

 

[John Larkin]

Does it exist? Would it work? Could it be extremely cheap? Does
anyone make a "small" surface mount pmos depletion device at all?

I don't know of any.


How about common-base?


in--------r-----------+
|
|
e
pnp b----gnd
c
|
|
+---------------out
|
r
|
|
-5


It's not perfect, admittedly. But the pnp would be very cheap.

John

 

[MooseFET]

I don't know of any.

How about common-base?

Better yet common emitter:

Modified drawing:

Vcc-------R1----------+
|
|
e
pnp b----Signal In
c
|
|
+---------------out
|
R2
|
|
-5

The modified works better with logic that pulls down better than up.
You don't want the resistors to be equal. They should be scaled to
make the gain to get the required output swing.


This circuit also has a nice feature that it is a near constant output
impedance.