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Use Two digital pots in 1 IC at different voltages
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Topic: Use Two digital pots in 1 IC at different voltages (Read 1301 times)
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Willemg12
Newbie
Posts: 3
Use Two digital pots in 1 IC at different voltages
«
on:
August 02, 2017, 05:05:32 pm »
To do a modernization of an old lab supply I want to replace the old pots with digital potentiometers.
TI and Linear Technology have good choices in that.
I want to steer these over SPI/I2C. The problem I face is that the digital potentiometer ICs cannot be used out of the rail to rail voltages. E.g. 0V-5V
Where I want to be one at the GND and the other at the VCC level. +24V
UPDATE. In the figure a schematic is shown with the two pots in.
So as this is out of spec for most ICs
what could be a solution for this?
Thank you
«
Last Edit: August 03, 2017, 09:35:20 pm by Willemg12
»
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Benta
Super Contributor
Posts: 5880
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Re: Use Two digital pots in 1 IC at different voltages
«
Reply #1 on:
August 02, 2017, 05:15:27 pm »
I'd check ON Semiconductor. ON acquired Catalyst, who were famous for their digital pots.
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Willemg12
Newbie
Posts: 3
Re: Use Two digital pots in 1 IC at different voltages
«
Reply #2 on:
August 02, 2017, 06:54:41 pm »
I did. ON has a pot that has Vh up to 16 V.
But in my case that will be not enough, as i work with 24 volts.
Should i use extra Elements..
Dunno...
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tszaboo
Super Contributor
Posts: 7392
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Current job: ATEX product design
Re: Use Two digital pots in 1 IC at different voltages
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Reply #3 on:
August 02, 2017, 07:04:11 pm »
Some AD parts, like AD7376 goes up to 30V. They dont work outside the suply rails, because they have FETs built in, switching stuff.
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Howardlong
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Re: Use Two digital pots in 1 IC at different voltages
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Reply #4 on:
August 02, 2017, 09:33:37 pm »
Microchip MCP41HV31/51 for SPI, MCP45HV31/51 for I2C, but they are only single pot per package. Up to 36V, or +/-18V.
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Zero999
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0999
Re: Use Two digital pots in 1 IC at different voltages
«
Reply #5 on:
August 02, 2017, 10:11:45 pm »
The schematics don't look right. Are they direct extracts from the service manual or the product of reverse engineering?
Is it not possible to use a DAC and suitable amplifier? Normally the voltage and current limits are controlled by a reference which is set by potentiometers. You can probably replace the potentiometers with voltage sources.
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Willemg12
Newbie
Posts: 3
Re: Use Two digital pots in 1 IC at different voltages
«
Reply #6 on:
August 03, 2017, 08:39:26 pm »
Thanks hero999 and all others
You were right. At first the only thing that i wanted was a direct change from analog to digital.
I included the schematic of my trustworthy old bench supply.
The pot P2 is easily interchangable (though i not favor the value of 1k) But what about P1....
Geven the fact that i want one uP control the device ...
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Benta
Super Contributor
Posts: 5880
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Re: Use Two digital pots in 1 IC at different voltages
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Reply #7 on:
August 03, 2017, 09:34:44 pm »
Something's still wrong... the power stage has no base drive.
Scratch that, I just untangled the 723 ground connection.
«
Last Edit: August 03, 2017, 09:37:44 pm by Benta
»
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