Slightly OT : Looking for High Voltage OPAMP Supplier

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Hello everybody,

I'm delving in an embedded project that needs among other things to move
some optical elements using some piezo PZT stack actuators . Big deal, I
thought in the beginning . The current drive requirements are low, short
pulses of up to 30mA , with a low duty cycle, and operating voltage of up to
60Vdc , single source .
 When it came the time to implement a solution, Apex came to mind .
Surprise, they only have now all sorts of high power devices ,
astronomically priced, in huge TO-3 or TO-220 packages, running up to
hundreds of volts and delivering up to several Amps in capacitive loads. I
started searching all the good old opamp makers and some specialty high
voltage opamp houses . Burr Brown, swallowed by TI, Elantec, swallowed by
Intersil, Analog DEvices, no high voltage , Maxim, no high voltage , Linear
Tech , no high voltage , Natsemi, no high voltage . Apex , lots of
1000V/10A/$100 devices , in TO-3 packages !
I looked at audio amps as well, in the hope of finding that elusive $2 ,
surface mount plastic package that would run at 60Vdc, which is what I need
. No such luck yet.

I'm asking here, although this is not strictly embedded , maybe someone
knows of a current produciton device with the following specs:
-opamp
-operating supply voltage up to 60Vdc , or higher , to allow an approximate
output swing of 60V , or split supply of  +/-30V or higher if not rail to
rail output , to allow the same output swing of 60v.
-max output current 30mA pulses shorter than 1ms , repeated with a max duty
cycle of 20% .
-plastic package, SMD .
-low cost, under $4.
-multiple , dual or quads would work even better.

Any pointers would be greatly appreciated.

thank you,
matt tudor





Re: Slightly OT : Looking for High Voltage OPAMP Supplier
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  As you have found, this is a little bit of no-mans-land : you need to
look for a volume usage device that can be used in your niche.

  Look at CRT drivers eg
http://www.national.com/parametric/0,1850,952,00.html

  These are high voltage, low cost, 3x, and have class AB drive, and
CRT drive is a large market segment, with a range of Speed/Voltage choices.
-jg



Re: Slightly OT : Looking for High Voltage OPAMP Supplier
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Matt;
Try looking at the L6660 MILLI-ACTUATOR DRIVER from ST. It is a resonant
converter that is able to drive +/-35V, or 0-70V at better than 60mA
with a 12V supply. I don't know anything the price or availability...
Otherwise take a look in Art of Electronics 2nd edition for the simple
piezo driver circuit. I have used that circuit and you easily implement
a variation of it that fits within your budget constraints.

Jay


Re: Slightly OT : Looking for High Voltage OPAMP Supplier


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Do you need accurate pulse amplitudes i.e. the output must be in the
op-amp feedback loop ?

Do you need both current sinking and sourcing capability ?

If only sinking capability needed, look for those NPN darlington
arrays with 7 or 8 transistors. If feedback is used, the feedback
resistors will drop the feedback voltage well below 30 V, so ordinary
30 V op-amps can be used to drive the darlingtons. The driving op-amp
output must be able to go to the negative supply (ground) in order to
fully cut off the darlingtons. Since there are a 7-8 drivers in each
IC, the chip count should not be a problem if multiple channels are
needed.

However, if both sinking and sourcing are needed, you would also have
to use some individual PNP transistors to sink the current, since I am
not aware of any PNP driver chips with multiple  common emitter
drivers. Additionally some resistors are needed, so the chip count can
be quite large when multiple channels are needed.

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The 60 Vdc supply would allow 20 Vrms or 50 or 100 W into 8 resp. 4
ohms, so no wonder that you did not find anything in that price class.
At least previously, a few high voltage driver ICs existed, which
required the addition of two high current, high power transistors to
make a complete 50-200 W audio amplifier.  Look for such driver ICs,
since they should alone be able to drive the 30 mA load.

Paul


Re: Slightly OT : Looking for High Voltage OPAMP Supplier

Paul Keinanen wrote in message ...
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to
need

I need analog outputs, not PWM or logic. The PZT actuators have nanometer
resolution and over 10 micron displacement range .

The audio driver stage Ic's that you're mentioning have disappeared from
product lines of all major maunfacturers that I am familiar with . 10-20
yearsd ago they were produced by multiple vendors, now they're gone ,
rpelaced by higher scale integration, switching integrated audio amplifiers
, etc.

The CRT video drivers come close but no cigar, because CRT's have low
capacitance , in the tens of pF , whereas the PZT actuators are in the tens
of nanos or larger .

The ST L6660 is the closest to my needs, just have to source it now, and a
search for it on major US distys websites failed .  The ST website shows a
datasheet for it dated 2000 , and marked preliminary . Doesn't smell good .

best regards,
matt tudor



Re: Slightly OT : Looking for High Voltage OPAMP Supplier
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Matt et all,

Assuming you need to reproduce a waveform @high voltage, the
TI/Burr-Brown OPA452 meets the electrical specs, but is (at ~$5 {price
from digikey}) a bit over the target price.  The Harris (now intersil)
HA-2645 will handle the voltage swing, but would need a push-pull pair
to handle the current.  Both are single channel devices.  So, the CRT
drivers may well be the better choice.  If you just need a short
pulse, why not use MOSFET(s) to switch?

A post to sci.electronics.design may garner more ideas.

HTH,

Larry

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