Range hood automatic controller circuit

Circuit working principle: As shown in Figure 4-44, R. , Rz and the negative temperature coefficient
thermistor RT, RT2 form a balanced temperature difference bridge , in which RT is installed near the air outlet of the range hood
, and RT2 is installed on the circuit board. When the stove is not ignited,
the ambient temperatures of brother L and RT2 are the same, the bridge remains balanced, and there is no signal output. When the stove is ignited
, a gradually lower temperature gradient field with the fire source as the center is formed around the stove.
The temperature at RT is higher, and the resistance value is much reduced; the temperature at RT2 is basically unchanged, or it is shorter and higher, and the resistance value is reduced less, thus making the bridge unbalanced and outputting a DC level
that is low at the bottom and high at the top.
Signal. Operational amplifier A, and R, etc. form a negative feedback amplifier.
The function of C3 is to prevent crosstalk of AC signals. The DC level signal sent from the thermodifference bridge
is amplified by A and outputs
a temperature difference signal of approximately 1 V/cC at the l pin of the dual operational amplifier LM358. The operational amplifier A2 and R6 form a common window voltage comparator
, which is installed as shown in the figure. The window width is about 1V, and the corresponding temperature f is about
1°C. This avoids the binary output signal of the operational amplifier A2 caused by slight temperature changes.
The number jumps back and forth.