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This is a universal thermostat, which can be used to switch. Used 220 V The author uses the circuit as a breeding thermostat. 220 V Thermostats Circuit Diagram :   The circuit is built around an opamp 741, which is the voltage of the voltage divider R1/R2/R3 compares with the reference voltage of R4/R5/P1. As the temperature rises, the resistance of the NTC fall's, causing the voltage drops to the positive input of the opamp. At some point the folded opamp to spert and the transistor T1 and the load is switched off. The turning point (or the shutdown temperature) is set to P1. Parts List: R1 = 6.8 kΩ R2, R3 = 1 kΩ NTC R4 = 12 kΩ R5 = 3.9 kΩ R6 = 820 Ω R7 = 27 kΩ R8 = 470 Ω R9 = 100 Ω P1 = 10 kΩ C1 = 470 μF C2 = 100 V nF/250 D1 = LED D2 - D5 = 1N4148 Of T1 = BC548 2N1613 T2 = TIC206M IC1 = 741 IC2 = K3020P

12 V AUDIO AMPLIFIER WITH TRANSISTOR ELECTRONIC DIAGRAM In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA.To measure this current, wire a DC current meter temporarily in series with the collector of Q3. List Component P1_____________10K Log.Potentiometer R1,R2__________33K 1/4W Resistors R3_____________33R 1/4W Resistor R4_____________15K 1/4W Resistor R5,R6___________1K 1/4W Resistors R7____________680R 1/4W Resistor R8____________120R 1/2W Resistor R9____________100R 1/2W Trimmer Cermet C1,C2__________10µF 63V Electrolytic Capacitors C3____________100µF 25V Electrolytic Capacitor C4,C7_________470µF 25V Electrolytic Capacitors C5_____________47pF 63V Ceramic Capacitor C6____________220nF 63V Polyester Capacitor C8___________1000µF 25V Electrolytic Capacitor D1___________1N4148 75V 150mA Diode Q1____________BC...

This circuit is also use operational amplifier IC LM324 to drive the VN64GA with the error signal and to control output voltage. This output voltage is pulsating DC , which is quite satisfactory for battery charging. This circuit also can be converted to the system regulated DC supply. You do this by increased C2 and anoother electrolytic capacitor is added across the load. The respon time is very fast, determined by the op amp. Schematic and troubleshooting below : If the circuit not work , Perhaps the cause of : AC cable disconnected Transformer is damaged or leaking.  Broken or leaky diode. Installation of inverted foot elco. Instrallation of the components of the upside , particularly on the transistor , examine the placement of the feet emitter , collector and base. IC damaged. Soldering is less sticky. Line PCB damaged.