J
Joerg
- Jan 1, 1970
- 0
Hi Folks,
Does anyone know a part that is small, can be used to command a certain
resistance and can be talked to across the usual mains-isolated barrier
of office equipment and the like? I need to set resistor values on the
mains side from a uC on the low voltage side. Has to be:
Linearity error from 0V to about 1V excitation should be <5%.
Absolute resistance tolerance <20% if possible.
Bandwidth for resistor value changes up to a few kHz.
No limit on the number of changes (meaning no EEPROM).
Addressable across isolation barrier.
So far I've considered:
a. FET optocouplers such as the H11F1. A bit pricey at over $1 but most
of all has the problem that the linearity goes to pots as soon as there
is more than 20-30mV across the FET, plus it needs a ton of drive power
for low resistance:
http://www.fairchildsemi.com/ds/H1/H11F1M.pdf
b. Digital potmeters such as the MCP4011 series. These are nice, tons of
bandwidth, cheap and small. But they do need an additional two-channel
optocoupler to get the command data across and the absolute resistance
value tolerance is borderline at 20%:
http://ww1.microchip.com/downloads/en/DeviceDoc/21978c.pdf
c. Servoed FET plus opto. The servo gets rid of the non-linearity. Done
it before but this gets old because it needs a lot of parts and real estate.
d. LDR plus LED: Very nice, but fairly large and most of all LDRs are
banned in some countries on account of their Cadmium content.
Any other miracle parts out there?
Does anyone know a part that is small, can be used to command a certain
resistance and can be talked to across the usual mains-isolated barrier
of office equipment and the like? I need to set resistor values on the
mains side from a uC on the low voltage side. Has to be:
Linearity error from 0V to about 1V excitation should be <5%.
Absolute resistance tolerance <20% if possible.
Bandwidth for resistor value changes up to a few kHz.
No limit on the number of changes (meaning no EEPROM).
Addressable across isolation barrier.
So far I've considered:
a. FET optocouplers such as the H11F1. A bit pricey at over $1 but most
of all has the problem that the linearity goes to pots as soon as there
is more than 20-30mV across the FET, plus it needs a ton of drive power
for low resistance:
http://www.fairchildsemi.com/ds/H1/H11F1M.pdf
b. Digital potmeters such as the MCP4011 series. These are nice, tons of
bandwidth, cheap and small. But they do need an additional two-channel
optocoupler to get the command data across and the absolute resistance
value tolerance is borderline at 20%:
http://ww1.microchip.com/downloads/en/DeviceDoc/21978c.pdf
c. Servoed FET plus opto. The servo gets rid of the non-linearity. Done
it before but this gets old because it needs a lot of parts and real estate.
d. LDR plus LED: Very nice, but fairly large and most of all LDRs are
banned in some countries on account of their Cadmium content.
Any other miracle parts out there?