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Analog Squarer {Y=X^2} 1 Quardrant

F

Fred Bartoli

Jan 1, 1970
0
Harry D a écrit :
Jim, As my question states, I only need one quadrant, the first or third, both inputs tied together.
I am trying to keep a MOSFET on for as long as possible, from releasing smoke on overload conditions, so tracking the I^2*T constant of FET and also need a temperature term which is strait forward. The FET current changes 10:1 so the "time on" changes 1:100.

Regards,
Harry

A reseted double integrator will do that nicely.
Release the integrators reset on your fault condition trig, then compare
the output to your wanted threshold...
 
S

Syd Rumpo

Jan 1, 1970
0
I have looked at the AD835 and other 4-Q multipliers but they are costly and power hogs. I need a simpler (+/-5% accuracy [-40C to 105C]) design that will be used in a high reliability product. Input range of 0.05V to 1.70V with a bandwidth of dc to at least 1.0MHz. Simplicity, small size, low power <50mW, SM implication and cost are a plus. I need some starter ideas for me to complete the design.

Cheers,
Harry

Lookup table in ROM.

Parallel ADC -> ROM Address bus.

ROM data bus -> parallel DAC.


Or...

Parallel ADC -> resistor network, aka custom non-linear DAC.


Cheers
 
P

P E Schoen

Jan 1, 1970
0
"Harry D" wrote in message
Jim, As my question states, I only need one quadrant,
the first or third, both inputs tied together.
I am trying to keep a MOSFET on for as long as possible,
from releasing smoke on overload conditions, so tracking
the I^2*T constant of FET and also need a temperature term
which is strait forward. The FET current changes 10:1 so the
"time on" changes 1:100.

You may want to monitor the safe operating area, or SOA, which involves both
current and voltage. See:
<http://www.infineon.com/dgdl/SOA_06...506db&fileId=db3a30433072cd8f0130b63abece21ad>

I think it would be most effective to use a PIC to monitor the parameters,
but it will not be fast enough to detect destructive transients.

Another analog option may be to use an incandescent lamp (perhaps driven by
an op-amp) to provide a signal based on i^2t.

You can also get self-protected MOSFETs:
http://www.onsemi.com/PowerSolutions/parametrics.do?id=819
http://www.silica.com/product/zxms6004ff-60-v-self-protected-intellifet-mosfet.html
http://www.irf.com/product-info/hexfet/ips.html

Paul
 
H

Harry D

Jan 1, 1970
0
Of course !-) Do the math...



Vbe = KT/q*LOGe(I/Is) where Is is the same for all 4 devices in the

MAT-04.



Equate the voltage drops down the two "legs" of the MAT-04, reduce

until you lose the LOGe. You're left with...



I1*I1 = IMOUT*I3



No temperature terms ;-)



In critical applications you might want to cascode collector, C4, to

avoid Early effect unbalancing the betas.



The 4-device (MAT-04) scheme is pretty robust... you can inject other

currents between Q1 and Q2, and between Q3 and Q4 and get various

interesting equations.



...Jim Thompson
Ok JT, You have won a bottle of Oban for your winning squarer circuit using the MAT14. It works great over my input range of 100uA to 1.0mA. AdvancedLinear Devices has low threshold (Vgs= 0V) matched FETS (ALD1106). Do you think they would track just as well?

Highest regards,
Harry
 
H

Harry D

Jan 1, 1970
0
Ok JT, You have won a bottle of Oban...

How do I claim the prize? Sounds marvelous!
...Jim Thompson

There is a bottle waiting for you at Costco. I will refund by PayPal.



Cheers,



Harry

JT, We need a full report on your taste for Oban whiskey and while you are at Costco, buy the Belgian Chocolate Cups from Kirkland. I deem them deli-sh!

Cheers,

Harry
 
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