linear speed control in betweenFrom point of view OpAmp outputs, basic NAND gate action
U1A U1B Q1 FAN
0 0 on on (does not exist)
0 1 on on 12 Vout
1 0 on on 5V out
1 1 off off (power off)
I should have qualified what I was posting, I fully realize this is a speed control system andlinear speed control in between
I understand your intent for "analogic" but only the two middle logic states exist with a linear temp-controlled fan voltage in between the two thresholds for U1B and U1A for Vfan from 5 to 12V.
- U1A is inverting linear operation between 7kohm to 4kohm while its output ranges from 11V(sat) to 10V (linear)
- then 0V (sat) when the PNP cannot pull-up any higher than 12V.
- U1B is non-inverting unity gain with Vol = "0" , "1' = 10V to 11V to drive Q1-b to regulate Fan @ 5V On for any temperature below 33'C
- When the temperature exceeds 33'C U1B goes out of regulation and saturates high and U1A takes over. (low man wins diode logic to regulate the fan.)
U1A varies between linearly inversely with temp between 7kohm to 4kohm =33'C and 47'C
for a std. 10k NTC thermistor.
OR:
A B Q
0 0 0
0 1 1
1 0 1
1 1 1
here
diodes here
A B Q
0 0 0
0 1 0
1 0 0
1 1 1 == AND
diodes to out
A B Q
0 0 1
0 1 1
1 0 1
1 1 0 == NAND
hiFrom point of view OpAmp outputs, basic NAND gate action
U1A U1B Q1 FAN
0 0 on on
0 1 on on
1 0 on on
1 1 off off
hi can you guide me how do i it?Positive feedback creates the hysteresis roughly by resistance ratios.
Do you know how to compute the sum of all currents on each resistor to determine the voltage hysteresis thresholds for U1C saturated states Voh, Vol?
Try it and let us know.
thanks for reply1) LM324 has limited VOH (VCC-2Vbe @ no load)
so R4, R5, D1 "ensure" that Q1 can be turned all the way
off. As long as things don't get too hot in Q1 anyhow.
2) Thermistor is a resistor and all by itself would just put
12V resistor limited on the temp sense line. R1 scales,
puts midrange and "makes live".
3) R12 makes Q2 base current / U1 supply andoutput
current reasonable (better than a 40mA short circuit
current limit will...)
4) positive feedback, (R10||R11)/R9 - same as any Schmitt,
only the details vary. A nice high impedance input and a
hidden (from that input's I-V) positive feedback of lesser
authority.
These are all pretty basic and not sure giving you easy
answers is helping, or just encouraging you not to think.
There are many op amp circuit design and appllication
papers and books out there (check archive.org for e-books)
that you might find entertaining if you like this stuff.
hi1) LM324 has limited VOH (VCC-2Vbe @ no load)
so R4, R5, D1 "ensure" that Q1 can be turned all the way
off. As long as things don't get too hot in Q1 anyhow.
2) Thermistor is a resistor and all by itself would just put
12V resistor limited on the temp sense line. R1 scales,
puts midrange and "makes live".
3) R12 makes Q2 base current / U1 supply andoutput
current reasonable (better than a 40mA short circuit
current limit will...)
4) positive feedback, (R10||R11)/R9 - same as any Schmitt,
only the details vary. A nice high impedance input and a
hidden (from that input's I-V) positive feedback of lesser
authority.
These are all pretty basic and not sure giving you easy
answers is helping, or just encouraging you not to think.
There are many op amp circuit design and appllication
papers and books out there (check archive.org for e-books)
that you might find entertaining if you like this stuff.
I'd like to see you try 1st using what you know.hi can you guide me how do i it?
hi and thanks for the replyI'd like to see you try 1st using what you know.
Let me use the datasheet to assume the LM324 output with 150K load goes from 10.6 to 0.1 with positive feedback to each rail.
Imagine the switch represents two two states with hystereis where the thermistor voltage input crosses these thresholds.
What are the upper and lower thresholds?
View attachment 185764
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