Hi all,
I have built a 3 stage Temperature-based Fan Controller to run off a single-rail DC supply of around 12-15V:
1) Wheatstone Bridge (with thermistor as one leg - all 10K resistors)
2) Instrumentation amplifier Instrumentation Amplifier (3 Op-Amp)
3) PWM Generator Basis of PWM Generator
The triangle wave outputs of circuit (2) and circuit (3) are passed into an Op-amp comparator. These output from this will go into digital buffer (4050) -> MosFET driver buffer (IR4288) -> MosFET (connected in ground path of the Fan(s)).
I have modded the PWM Generator a bit as I am using a single supply and I have added in digital buffers (from a 4050 chip) to get a higher trangular wave amplitude.
The PWM frequency is around 20KHz.
Anyway I want to determine the maximum of a number of seperate temperature points... I need someone to reality check this solution I have come up with!!
Basically I propose to have multiple sensors each with duplicate builds of the first 2 stages of the circuit:
1) Wheatstone Bridge+sensor 1 1) Wheatstone Bridge+sensor 2 ...
2) Instrumentation amplifier 2) Instrumentation amplifier ...
*********************************** THE QUESTION IS HERE.... !!! ********
Then I combine all the outputs from 3 instrumentation amplifiers, which will be a DC voltage of 1.2-10.8V above ground (i.e. Op-amp hitting supply rails). I do this by passing each output first through a Schotky diode (to minimise forward drop). The $1,000,000 question is: ' Will I end up with combined output which is the maximum DC voltage of 3 output voltages??'
********************************************************************
I am not quite clear what happens if I link 2+ diodes at the cathode when the anodes are driven by different DC voltages?? Anyone able to clarify this? I ran a simple 2 diode circuit through Spice (last year I think) which seemed to imply that I would get the maximum of the input voltages at the output... But will I also get any evil short circuits or other such nasties??
Thanks for any help you can give in this matter!!
Bob Wya
I have built a 3 stage Temperature-based Fan Controller to run off a single-rail DC supply of around 12-15V:
1) Wheatstone Bridge (with thermistor as one leg - all 10K resistors)
2) Instrumentation amplifier Instrumentation Amplifier (3 Op-Amp)
3) PWM Generator Basis of PWM Generator
The triangle wave outputs of circuit (2) and circuit (3) are passed into an Op-amp comparator. These output from this will go into digital buffer (4050) -> MosFET driver buffer (IR4288) -> MosFET (connected in ground path of the Fan(s)).
I have modded the PWM Generator a bit as I am using a single supply and I have added in digital buffers (from a 4050 chip) to get a higher trangular wave amplitude.
The PWM frequency is around 20KHz.
Anyway I want to determine the maximum of a number of seperate temperature points... I need someone to reality check this solution I have come up with!!
Basically I propose to have multiple sensors each with duplicate builds of the first 2 stages of the circuit:
1) Wheatstone Bridge+sensor 1 1) Wheatstone Bridge+sensor 2 ...
2) Instrumentation amplifier 2) Instrumentation amplifier ...
*********************************** THE QUESTION IS HERE.... !!! ********
Then I combine all the outputs from 3 instrumentation amplifiers, which will be a DC voltage of 1.2-10.8V above ground (i.e. Op-amp hitting supply rails). I do this by passing each output first through a Schotky diode (to minimise forward drop). The $1,000,000 question is: ' Will I end up with combined output which is the maximum DC voltage of 3 output voltages??'
********************************************************************
I am not quite clear what happens if I link 2+ diodes at the cathode when the anodes are driven by different DC voltages?? Anyone able to clarify this? I ran a simple 2 diode circuit through Spice (last year I think) which seemed to imply that I would get the maximum of the input voltages at the output... But will I also get any evil short circuits or other such nasties??
Thanks for any help you can give in this matter!!
Bob Wya
