It is for measuring furnace temperature
Vout = 1.21V * (1 + (R2/R1)) + (Iadj) * (R2)
because it is a 12V 350mA BLDC motor.
Hi,
Thanks for all the info. Super. Apology: I have a job I need to finish by 9AM my time, so need to hurry a little bit.
Just reviewing the schematic "quickly" - and without having done any voltage regulator PD calculations - my personal observations and opinions are:
Trimpots: Good practice is not to set trimpots anywhere near the high/low ends of the range. It's recommended to use a fixed value resistor in conjunction with a trimpot whose wiper ideally doesn't travel much away from approximately half the trimpot value, ~42k is a little far for my liking but should be fine.
The motor on the same line as the 3.3V regulator input: !!! OMG!. Don't do that, I think. That voltage line will presumably have transient dips on it when the motor turns on and when it turns off the output of the 12V will get the back emf kickback. If the PD of the 3.3V regulator when connected to the 16V regulator is within the permitted for the part, I'd put it in parallel with the 12V regulator. I'd personally have paralleled all three regulators from the main input rather than cascade them as they all have a job to do, but again, it depends on PD of each regulator.
The motor needs a flyback diode, and a 100nF across the motor terminals won't hurt. I'd possibly be OTT and consider a series diode at the output of the 12V regulator and factor in its voltage drop to get 12V + expected diode Vf as the regulator output voltage.
I'm far from being an expert like many members here but hope the comments are helpful. I'll be back, like the proverbial bad penny.
So, I will not be using trimmer at extremes to get these values. Or should I use a say a 5k resistor in series with trimmer wiper ?
So, should I parallel the 3.3V regulator circuit with 12V regulator circuit or series as in the attached will do ? Which is better ? because the LDO has to drop 20V to 3.3V. If used in parallel mode. In series mode it is dropping 12V to 3.3V.
Practically which circuit is better from the 2 attached ?
For U1,U2 and U3 sense pins I am using 100k pullup resistors and for U1 I have a connection betweeen SENSE pin and microcontroller 3.3V pin. Is that fine ? Or should I use a NPN transistor to make the SENSE pin low to turn Off battery charging retaining the 100k pull-up resistor ? because there will be max 20V at SENSE pin and microcontroller is 3.3V type (PIC18LF26K22).
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