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Fan Temperature Controller Circuit Diagram (BZX79C18)

2015-03-01 07:26  
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This circuit controlled the speed of fan related to the temperature changes. Using without IC usage, thermistor (R1) and linear potentiometer (P1) generate a temperature sensitive variable voltage. R3-R4 and P1-R1 are wired as a wheatstone bridge. R3-R4 generate a fixed two-third supply reference voltage, and Q1 used as bridge balance detector.

This article describes a Fan Temperature Controller Circuit Diagram (BZX79C18). The content is very simple, very helpful. Components in this article can help you understand better understanding of this article. For example, in this article, you can go to find and buy these components:BZX79C18.



P1————————————————-22K linear potentiometer

R1————————————————-15K @20c n.t.c thermistor

R2————————————————-100K 1/4W resistor

R3,R6———————————————10K 1/4W resistors

R4,R5———————————————22K 1/4W resistors

R7————————————————-100R 1/4W resistor

R8————————————————-470R 1/4W resistor

R9————————————————-33K 4W resistor

C1————————————————-10nF 63V polyester capacitor

D1————————————————BZX79C18 18V 500mW zener diode

D2————————————————TIC106D 400V 5A SCR

D3-D6——————————————-1N4007 1000V 1A diodes

Q1,Q2——————————————-BC327 45V 800mA PNP transistors

Q3————————————————BC337 45V 800mA NPN transistor

SK1———————————————–female main socket

PL1———————————————–male main plug and cable

P1 is adjustable, so that the reference and variable voltage are equal at a temperature just below the require trigger value, and under this condition Q1 base and emitter are at equal voltage and Q1 cut off. When R1 goes above this balance value, the P1-R1 voltage falls below the reference value, so Q1 become forward biased, pulse charging C1. This occurs because the whole circuit is supplied by 100Hz half wave voltage obtained by main supply by means D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and zener diode D1. The 18V supply is not true DC but has rather trapezoidal shape. C1 provides a phase delay pulse train related to temperature and synchronous with the main supply zero voltage point of each half cycle. Thus producing minimal switching RFI from the SCR. Q2 and Q3 from a trigger device, generating a short pulse suitable to drive the SCR.

This circuit are design for 230 VAC operation, the operating function can be reversed by changing the R1 and P1 position. Its available to use 10K-22K variation value of thermistor.


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