- Fri Feb 17, 2017 10:24 pm
#62723
Since the device is to be battery powered AusUser wanted an implementation that was power efficient. In my post I described a way to accomplish AusUser's goals without using a power consuming relay. There already is an input to disable the charging function and a simple level conversion is all that is needed. I don't know why you are so concerned about the voltage handling capability of the mosfet. The suggested devices switch properly with the ~3 volt logic level of the ESP8266.
Just to make it clear, there is no relay required for what I suggested. A high side switch is also not required. Do you see any reason not to use the charge disabled function already present in the chip?
picstart wrote:An issue to consider is the voltage to be switched. A relay can switch almost any voltage so long as its coil can be driven. For a relay the coil voltage can be 3v and yet it can switch say 100v. Now a FET can only switch well if the gate voltage is as high as the voltage to be switched so a FET switching say 12v needs to have its gate voltage at close to 12v otherwise it is not fully on and will have a meaningful resistance between the source and the drain. There are solid state solutions but they involve things like high side drivers.
Since the device is to be battery powered AusUser wanted an implementation that was power efficient. In my post I described a way to accomplish AusUser's goals without using a power consuming relay. There already is an input to disable the charging function and a simple level conversion is all that is needed. I don't know why you are so concerned about the voltage handling capability of the mosfet. The suggested devices switch properly with the ~3 volt logic level of the ESP8266.
Just to make it clear, there is no relay required for what I suggested. A high side switch is also not required. Do you see any reason not to use the charge disabled function already present in the chip?
