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Level Shifter 3.3V to 28V

Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??
 
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

How about logic level N fets and pull up resistors? I am assuming your
3.3v signal is really ground to 3.3V, and you want ground to 28v out.
Granted, the n-fet scheme will invert the signal.
 
E

Eeyore

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

How low ?

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

Exactly, use the 28V supply from the destination equipment.

How can I do this??

Doing it with discretes is probably simplest. How fast do they need to switch ?
What's the load capacitance etc ?


Graham
 
E

Eeyore

Jan 1, 1970
0
How about logic level N fets and pull up resistors? I am assuming your
3.3v signal is really ground to 3.3V, and you want ground to 28v out.
Granted, the n-fet scheme will invert the signal.

Yes. That's pretty much what I'd suggest. Bipolar transistors might prove easier
to source than 3.3V threshold mosfets though.

If this is in the design stage, dealing with the signal inversion would be
trivial.

Graham
 
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

SN7406.

http://focus.ti.com/lit/ds/symlink/sn7406.pdf

You'll probably need to set up a 5V rail to drive the 7406. but its
inputs are guaranteed to treat anything higher tha 2V as a "1" so 3.3V
signals should drive it okay.

A common-emitter array of NPN transistors could do the same job, but
you'd need a resistor in series with each base to limit the base
current. A common-source array of N-channel MOSFETs could skip the
gate resistors, saving you a bit more space and the "on" base current.
 
E

Eeyore

Jan 1, 1970
0
A common-emitter array of NPN transistors could do the same job, but
you'd need a resistor in series with each base to limit the base
current.

Rohm's (and others) 'digital transistors' integrate this base resistor now.

Check out DTA114 for example.

Graham
 
J

John Devereux

Jan 1, 1970
0
Eeyore said:
ULN2803A?


Yes. That's pretty much what I'd suggest. Bipolar transistors might
prove easier to source than 3.3V threshold mosfets though.

If this is in the design stage, dealing with the signal inversion would be
trivial.

Of course this is the straighforward solution if inversion is not a
problem - but to make it more interesting how about a "common base"
switch?


.. +28---------------------------
.. |
.. load
.. |
.. 3V3 |
.. | |/
.. |-[R]---| NPN (or logic level NMOS, without R)
.. | |\>
.. | |
.. | |
.. ------- |
.. | |
.. 3V3 |----
.. Logic |
.. |
.. |

(He said he only needed low current)
 
W

Winfield

Jan 1, 1970
0
SN7406.

http://focus.ti.com/lit/ds/symlink/sn7406.pdf

You'll probably need to set up a 5V rail to drive the 7406. but its
inputs are guaranteed to treat anything higher tha 2V as a "1" so 3.3V
signals should drive it okay.

A common-emitter array of NPN transistors could do the same job, but
you'd need a resistor in series with each base to limit the base
current. A common-source array of N-channel MOSFETs could skip the
gate resistors, saving you a bit more space and the "on" base current.

One popular seven-line switching IC from the old days is
TI's uln2003, rated at 50 volts max. TI's cost: 64 cents,
Toshiba: 55 cents, and ST: 43 cents. Get TI at 22 cents,
qty 1k. Mouser has tens of thousands in stock, in various
packages, etc., and can ship nearly a million in 10 days.
DigiKey has about 150k parts in stock and will ship you
75k on reels for 19 cents each, this afternoon.

Yep, that one is a true jellybean!

If benn has a uP signal source, he may want to consider
Allegro's a6b273 or a6b595. The latter are replacements
for TI's tpic6b273 and tpic6b595. The '373s use a byte-
wide input latch and the '595s use a shift register.
 
F

Fred Bloggs

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

That is not a "level shifter" technically, which means to preserve the
original signal shifted to a new DC baseline. You need a simple 28V
switch with a 3.3V input. In the logic world, 28V is *high voltage*, and
since the circuit is communicating with non-logic types of loads, it
would be called an *interface*. So you want to look under the interface
category of "chips."
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

How can I do this??

Check Power Logic series buffers from TI.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
J

John Larkin

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

A few dual opamps, maybe, running open-loop.

John
 
J

Jim Thompson

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

What does "convert" mean? 0 to 3.3V => 0 to 28V "logic"?

...Jim Thompson
 
J

Joseph H Allen

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

Look at half-hbridge interface ICs, for example: SN754410 or L293D. In some
applications these are nicer than the open collector chips: they actively
pull up as well as down and will work with 3.3V inputs, but they do need a
5V supply.
 
J

John Fields

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

---
Open-collector voltage comparators. View in Courier:


Vcc
| +28
[R1] Vcc |
| | [10K]
+----|-\ |
| | >--+-->OUT1
IN1>----|----|+/
| U1A +28
| LM339 |
| [10K]
+----|-\ |
| | >--+-->OUT2
IN2>----|----|+/
| U1B +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT3
IN3>----|----|+/
| U1C +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT4
IN4>----|----|+/
| U1D +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT5
IN5>----|----|+/
| U2A +28
| LM393 |
| [10K]
+----|-\ |
| | >--+-->OUT6
IN6>----|----|+/
| |U2B
[R2] GND
|
GND

For R1 and R2, set the ratio so that the voltage at the inverting
inputs of the comparators is halfway between Voh and Vol of your
logic.
 
J

Jim Thompson

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

---
Open-collector voltage comparators. View in Courier:


Vcc
| +28
[R1] Vcc |
| | [10K]
+----|-\ |
| | >--+-->OUT1
IN1>----|----|+/
| U1A +28
| LM339 |
| [10K]
+----|-\ |
| | >--+-->OUT2
IN2>----|----|+/
| U1B +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT3
IN3>----|----|+/
| U1C +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT4
IN4>----|----|+/
| U1D +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT5
IN5>----|----|+/
| U2A +28
| LM393 |
| [10K]
+----|-\ |
| | >--+-->OUT6
IN6>----|----|+/
| |U2B
[R2] GND
|
GND

For R1 and R2, set the ratio so that the voltage at the inverting
inputs of the comparators is halfway between Voh and Vol of your
logic.

What? No hysteresis ?:) Smirk-Smirk ;-)

...Jim Thompson
 
J

John Fields

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

---
Open-collector voltage comparators. View in Courier:


Vcc
| +28
[R1] Vcc |
| | [10K]
+----|-\ |
| | >--+-->OUT1
IN1>----|----|+/
| U1A
| LM339

<snip>

or, better yet:


Vcc
| +28
[R1] +28 |
| | [10K]
+----|-\ |
| | >--+-->OUT1
IN1>----|----|+/
| U1A
| LM339
 
J

John Fields

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

---
Open-collector voltage comparators. View in Courier:


Vcc
| +28
[R1] Vcc |
| | [10K]
+----|-\ |
| | >--+-->OUT1
IN1>----|----|+/
| U1A +28
| LM339 |
| [10K]
+----|-\ |
| | >--+-->OUT2
IN2>----|----|+/
| U1B +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT3
IN3>----|----|+/
| U1C +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT4
IN4>----|----|+/
| U1D +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT5
IN5>----|----|+/
| U2A +28
| LM393 |
| [10K]
+----|-\ |
| | >--+-->OUT6
IN6>----|----|+/
| |U2B
[R2] GND
|
GND

For R1 and R2, set the ratio so that the voltage at the inverting
inputs of the comparators is halfway between Voh and Vol of your
logic.

What? No hysteresis ?:) Smirk-Smirk ;-)

...Jim Thompson
 
SN7406.

http://focus.ti.com/lit/ds/symlink/sn7406.pdf

You'll probably need to set up a 5V rail to drive the 7406. but its
inputs are guaranteed to treat anything higher tha 2V as a "1" so 3.3V
signals should drive it okay.

A common-emitter array of NPN transistors could do the same job, but
you'd need a resistor in series with each base to limit the base
current. A common-source array of N-channel MOSFETs could skip the
gate resistors, saving you a bit more space and the "on" base current.

Thanks! I think this might work best for me.. a simple dip with 6
inputs and 6 outputs is ideal! Switching time is not a concern, and
the inversion I can take care of in the FPGA so no biggie there, but
I do have a dumb question, the data sheet for the SN7406N shows that
VCC should be 7 Volts, and that the output will be 30V.. it doesnt
require the high voltage as an input to chip, whats the theory on how
this chip works?
 
J

John Larkin

Jan 1, 1970
0
Id like to convert six 3.3v level signals to 28v signals. Very low
current.

I've found some ICs, but they only convert 1 signal each and they
internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to
generate or charge pump from the low to high voltage. Im just looking
for an IC that takes the 3.3v signals and switches it to 28V when 28V
is provided to the IC.

How can I do this??

---
Open-collector voltage comparators. View in Courier:


Vcc
| +28
[R1] Vcc |
| | [10K]
+----|-\ |
| | >--+-->OUT1
IN1>----|----|+/
| U1A +28
| LM339 |
| [10K]
+----|-\ |
| | >--+-->OUT2
IN2>----|----|+/
| U1B +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT3
IN3>----|----|+/
| U1C +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT4
IN4>----|----|+/
| U1D +28
| |
| [10K]
+----|-\ |
| | >--+-->OUT5
IN5>----|----|+/
| U2A +28
| LM393 |
| [10K]
+----|-\ |
| | >--+-->OUT6
IN6>----|----|+/
| |U2B
[R2] GND
|
GND

For R1 and R2, set the ratio so that the voltage at the inverting
inputs of the comparators is halfway between Voh and Vol of your
logic.

Use opamps, get active pullup, less parts, and possibly less power
consumption, depending on how hard the load needs to be pulled up,
which isn't specified here.

John
 
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