Author Topic: OP Schematic Voltage to Current Converting ExpLog  (Read 1361 times)

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Offline richiTopic starter

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OP Schematic Voltage to Current Converting ExpLog
« on: August 23, 2018, 07:41:51 pm »
Hi,

i want to make Voltage to Current converting, but not linear, i need it ExpLog.

0-5V is the Control Voltage for Input to the OPV.
Output is like an LED with breakdown voltage 2-4V and its have a treshold current, example 50-200mA
Now i want the 0-5V translate it to "treshold current" -> 1A
If 0V then treshold current goes to 0mA and if  0,1V then start treshold Current and makes it exponetial function to the max values.

Any idea ?

 

Offline Signal32

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #1 on: August 23, 2018, 11:28:22 pm »
I assume you didn't nt want to go the door gital route ? ADC + Micro + DAC ? Then you can do whatever you want with conversion.
 

Offline richiTopic starter

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #2 on: August 24, 2018, 12:20:59 pm »
Hi Signal32,

I would like to implement the purely analog, otherwise there would be time delays, and i need it up to 100kHz.
analog digital would certainly be a fine solution, but the effort would be too big, because I need the whole at least 3 times
 

Offline MasterT

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #3 on: August 24, 2018, 12:43:02 pm »
Can't see a point to have 100kHz (10 usec) response time for LED.  Visual perception by human being is more than 40 milliseconds, AFAIK, though 25 Hz should be sufficient.
 

Offline richiTopic starter

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #4 on: August 24, 2018, 12:48:48 pm »
it's not about the LED and the viewing with the eye. I'm only interested in the analog circuit with operational amplifiers.
 

Offline eev_carl

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #5 on: August 24, 2018, 02:00:17 pm »
There's a linear to exponential voltage converter in the middle of this DIY Synth page.  I think you can leave off the second op amp if you don't care about converting the result back to a voltage.

https://www.allaboutcircuits.com/projects/diy-synth-series-vco/
 

Offline exe

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #6 on: August 24, 2018, 03:07:17 pm »
AFAIK all log/exp circuits based on PN-junction suffer from serious temperature drift. Never seen this addressed.
 

Offline David Hess

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Re: OP Schematic Voltage to Current Converting ExpLog
« Reply #7 on: August 24, 2018, 07:32:50 pm »
AFAIK all log/exp circuits based on PN-junction suffer from serious temperature drift. Never seen this addressed.

The PN junctions are either used in matched pairs with a 3300ppm/C resistor or a single PN junction is ovenized.  Either is a very routine circuit when translinear accuracy over temperature is required.

 


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