J
Jim Thompson
Got a 28V rail-to-rail-output device in mind, John ?
...Jim Thompson
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Got a 28V rail-to-rail-output device in mind, John ?
...Jim Thompson
J
John Larkin
Got a 28V rail-to-rail-output device in mind, John ?
...Jim Thompson
There are lots around, but they're not super cheap. The load, and its
swing requirements, aren't specified, so we don't know how close it
has to swing, or indeed if it has to pull down at all.
We designed a pulse generator, actually a laser driver, a couple of
months ago. It puts a 75-volt, 250 ps wide pulse into 50 ohms, up to a
few MHz max. At one point, we needed to go from ecl (0.8 volt swing)
to the gate of a gaasfet, with ideal swing from about -2 (to turn it
off) to about +0.5 (to enhance it a bit.) The ideal logic level
shifter turned out to be an opamp! An AD8009 does it in about 600 ps.
John
E
Eeyore
Those are the MAXIMUM voltage ratings i.e. not a problem.
Graham
J
John Devereux
Eeyore said:
I think he may be missing the point that it is *open collector*,
i.e. the outputs only "pull down". You need resistors (or the load
itself) to 28V to "pull up".
J
John Fields
Got a 28V rail-to-rail-output device in mind, John ?
...Jim Thompson
There are lots around, but they're not super cheap. The load, and its
swing requirements, aren't specified, so we don't know how close it
has to swing, or indeed if it has to pull down at all.
---
Blah, blah, blah, blah, blah.
He said the load on the +28 was "very low", and even if nothing on
his end needs to be pulled down, my pulling 28V down to ground thru
10k and a 339/393 open collector will get pretty close to 0V. I
suspect that what he's got on his end is a resistor pulled up to +28
on his end which need to be externally pulled down, and if that's
the case my pullups can go away with an attendant lowering
minimizing of the NPN's Vce(sat) . Maybe he'll post back and we can
find out, even though he seems to be interested in Sloman's _REAL_
TTL solution.
J
John Larkin
On Wed, 28 Nov 2007 11:59:56 -0800, John Larkin
On Wed, 28 Nov 2007 11:48:29 -0600, John Fields
On Wed, 28 Nov 2007 00:56:02 -0800 (PST), [email protected] wrote:
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
Got a 28V rail-to-rail-output device in mind, John ?
...Jim Thompson
There are lots around, but they're not super cheap. The load, and its
swing requirements, aren't specified, so we don't know how close it
has to swing, or indeed if it has to pull down at all.
---
Blah, blah, blah, blah, blah.
He said the load on the +28 was "very low", and even if nothing on
his end needs to be pulled down, my pulling 28V down to ground thru
10k and a 339/393 open collector will get pretty close to 0V. I
suspect that what he's got on his end is a resistor pulled up to +28
on his end which need to be externally pulled down, and if that's
the case my pullups can go away with an attendant lowering
minimizing of the NPN's Vce(sat) . Maybe he'll post back and we can
find out, even though he seems to be interested in Sloman's _REAL_
TTL solution.
Since the load and the swing requirements are unspecified, there's not
a lot of point arguing the details. Open-loop opamps are sometimes
handy in these situations: pullup/pulldown drive, high voltage swing,
no external components, low quiescent current, built-in current
limiting, cheap and available.
I thought it was about electronics, almost on-topic in s.e.d. I
suppose you're not interested in fast level shifters, working with
555's mostly.
And I didn't say "me", I said "we." I didn't design this particular
level shifter, I just thought it was cool.
John
J
Jamie
keep in mind the SN7406 will invert your signal. If that isn't a problem
so be it.
The outputs are open-collectors. You need to supply a pull up from
the 28 volt supply to each output.
Select a resistor giving you the minimum current required for your
application while not exceeding the sink rating of the output.
W
Winfield
John said:John said:John said:Jim Thompson wrote:
John Larkin wrote:
John Fields wrote:
[email protected] wrote:
Id like to convert six 3.3v level signals
to 28v signals. Very low current.
... I'm just looking for an IC that takes
the 3.3v signals and switches it to 28V ...
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.
Got a 28V rail-to-rail-output device in mind, John ?
There are lots around, but they're not super cheap. The load, and its
swing requirements, aren't specified, so we don't know how close it
has to swing, or indeed if it has to pull down at all.
Since the load and the swing requirements are unspecified, there's not
a lot of point arguing the details. Open-loop opamps are sometimes
handy in these situations: pullup/pulldown drive, high voltage swing,
no external components, low quiescent current, built-in current
limiting, cheap and available.
I thought it was about electronics, almost on-topic in s.e.d. I
suppose you're not interested in fast level shifters, working with
555's mostly.
And I didn't say "me", I said "we." I didn't design this particular
level shifter, I just thought it was cool.
What's wrong with TI's robust 7-line level-shifting IC? The
uln2003 7-unit Darlington-transistor IC is rated for 50 volts,
and costs as little as 43 cents each, at Mouser and DigiKey.
http://focus.ti.com/docs/prod/folders/print/uln2003a.html
Hey, it's a jellybean! Pick your pullup-resistor values,
connect your logic signals, and go for it!
S
Spehro Pefhany
That would sure be my choice if the pullup and Darlington drop are not
concerns. It works fine with 3.3V CMOS levels. Orginally a Sprague
product, IIRC. Of course if you have an extra 5V supply that needs a
30-50mA load on it for some reason, the TTL 7406/7 might look
attractive.
Best regards,
Spehro Pefhany
R
Robert Latest
John said:
OK, here's something about _me_: I built a few drivers for "normal clocks"
yars ago and used LM358s for the 24V H-bridges. Back then I was stupid and
forgot the freewheel diodes for the inductive load, but heck, all these
units have been putting out their minute-pulses flawlessly for some 12 years
now.
robert
R
Robert Latest
I wonder how someone can use an FPGA but be stumped by the simplest of data
sheets. Is this what EE is all about nowadays?
Heck, I wouldn't touch an FPGA with a ten-foot pole but I sure know my
basics.
robert
R
Robert Latest
John said:
Well, just yesterday I designed-in a 555 (a 7555, actually) for the first
time in m,y life. I need an oscillator whose frequency can be changed over a
range of at least 200:1 with a 100k 10-turn pot. You need something with
some oomph to whack that timing cap around with R < 500 ohms.
Anything better for this than the 555? 100k is the limit for the pot because
they get pricey for higher values.
robert
T
Tim Williams
Robert Latest said:
Sure. Do it by voltage.
http://webpages.charter.net/dawill/Images/Triangle.gif
With Ct = 680pF, Fmin = 1Hz, Fmax = 4.5MHz. With Ct = 0 (stray breadboard
capacitance only), Fmax = 33MHz(!). That 2N4403 is doing an amazing 10ns
square wave edge when the state flips.
Since it's just a diff pair, you can use your imagination to tweak it to,
say, variable ON and OFF points. This is essentially a reduced 555 with a
CCS tacked onto the capacitor to make a clean triangle.
Tim
J
Jan Panteltje
74HC4046 PLL use the VCO.
It is linear too, pot as voltage divider.
J
John Fields
On Wed, 28 Nov 2007 13:23:09 -0700, Jim Thompson
On Wed, 28 Nov 2007 11:59:56 -0800, John Larkin
On Wed, 28 Nov 2007 11:48:29 -0600, John Fields
On Wed, 28 Nov 2007 00:56:02 -0800 (PST), [email protected] wrote:
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
Got a 28V rail-to-rail-output device in mind, John ?
...Jim Thompson
There are lots around, but they're not super cheap. The load, and its
swing requirements, aren't specified, so we don't know how close it
has to swing, or indeed if it has to pull down at all.
---
Blah, blah, blah, blah, blah.
He said the load on the +28 was "very low", and even if nothing on
his end needs to be pulled down, my pulling 28V down to ground thru
10k and a 339/393 open collector will get pretty close to 0V. I
suspect that what he's got on his end is a resistor pulled up to +28
on his end which need to be externally pulled down, and if that's
the case my pullups can go away with an attendant lowering
minimizing of the NPN's Vce(sat) . Maybe he'll post back and we can
find out, even though he seems to be interested in Sloman's _REAL_
TTL solution.
Since the load and the swing requirements are unspecified, there's not
a lot of point arguing the details.
---
then why are you?
---
---
Except for the reference divider?
---
---
Sounds like lots details to me...
Built in current limiting?
Geez, John, I think most of us aren't worried about that except, as
it relates to this case, that we keep the current through the sink
to less than that which will result in a logic '1'.
Got an example less expensive than an LM339/LM393 and a few
resistors?
---
J
John Fields
---
As it turns out, nothing. Originally the OP didn't mention that
inverting wasn't a problem, but had it been that would have ruled
out the TI part unless a set of inverters was placed in front of it.
E
Eeyore
Robert said:
Quite likely.
Graham
R
Robert Latest
Jan said:
Yeah, but the f range is way too limited. Tim's circuit is great, but I need
dozens of those so I'd prefer an integrated solution.
robert
J
John Fields
T
Tim Williams
Robert Latest said:
Only dozens I guess? But Jeorg is always complaining about integrated
solutions being so expensive! But I guess that's at a thousand dozen,
rather than just a dozen. :^)
If you like the 555, you can easily add some parts (like one or two CCS's,
which could be as little as a transistor, two resistors and a 10k pot) and,
if you want really long run time, a JFET or bifet op-amp follower between
the capacitor and pins 2 and 6 to minimize leakage. It's the wide range
CCS (from about 5nA -- leakage current -- to 15mA full bias) and JFET
follower (pA leakage?) that allow my circuit to cover such a wide range.
The "decision" part can just as well be a 555, though it won't run as fast,
if that mattered.
Tim (loves discrete)
