Simple DC power delay circuit

jacky May 25, 2010 7 Comments
Description. The circuit diagram shown here is of a simple DC power delay circuit that is based on an SCR. This circuit is a very handy one and can be employed in many applications. The working of this circuit is very simple. When the input power is applied the capacitor C2 charges through resistor R2 and when the voltage across the capacitor just exceeds the Zener diode D3’s breakdown voltage, it breaks down and the SCR H1 is triggered...
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Fuse with status indicator.

john August 4, 2009 No Comments
Description. Here is the circuit diagram of a fuse that has an automatic status indicator. This circuit can be added to circuit that operates from 12V DC. As long as the fuse is intact, the LED D3 will glow continuously and when the fuse blows off the LED will start and continue blinking. The first part of the circuit includes an astable multivibrator built around transistors Q1 and Q2.The output of the multivibrator is coupled to the base of...
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Temperature controlled fan regulator

john July 8, 2009 34 Comments
Description. This fan regulator circuit will automatically control the speed of your fan according to the temperature. Two thermistors (R1 and R2) are used to sense the temperature. The circuit works almost like the published here previously. Here the potentiometer is replaced by the thermistors. When the temperature is increasing the resistance of NTC thermistor ( R1) decreases and at the same time the resistance of PTC thermistor (R2) increases. At the same time, rate of change of the...
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Brightness controller for low power lamps.

admin November 16, 2011 6 Comments
Description. The circuit given here can be used to control the brightness of low power incandescent lamps. The circuit is based on IC NE555 which is wired as an astable multivibrator with variable duty cycle. The output of IC is connected to the base of transistor Q1.The Q1 drives the lamp. The duty cycle of the multivibrator can be varied by varying the POT R4.As a result, the brightness of the lamp varies according to the position of the...
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Temperature controlled DC fan

admin August 30, 2008 10 Comments
Description. Here is a simple circuit based on two transistors that can be used to control the speed of a 12 V DC fan depending on the temperature.A thermistor (R1) is used to sense the temperature. When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of...
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Modified lamp dimmer circuit

admin January 24, 2012 18 Comments
Description. This is a modification of the circuit Simple Lamp Dimmer/Fan Regulator  previously  posted here. The working of the circuit is same as that of the previous, but in addition a snubber circuit consisting of resistor R4 and capacitor C3  is included to improve the performance of the triac T1. A fuse is also included for better safety. I think this is the better circuit to try . Circuit diagram with Parts list . Notes. No matter how  what...
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PWM Motor Speed Control Circuit

admin November 15, 2011 9 Comments
PWM Motor Speed Control Description Here is a simple PWM motor speed controller circuit that can be used for varying the speed of low power DC motors . The variation in speed is achieved by varying the duty cycle of the pulse supplied to drive the motor. Of the two gates of IC CD40106B , N1 is wired as an inverting Schmitt Trigger astable multi vibrator for producing pulses and N2 as an inverting buffer to drive the transistor...
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Simple Lamp Dimmer/ Fan Regulator

admin November 22, 2011 33 Comments
A Lamp Dimmer/Fan Regulator Circuit We have modified this circuit: – Take a look – Modified Lamp Dimmer Description . This is the circuit diagram of the simplest lamp dimmer or fan regulator.The circuit is based on the principle of power control using a Triac.The circuit works by varying the firing angle of the Triac . Resistors R1 ,R2 and capacitor C2 are associated with this. The firing angle can be varied by varying the value of any of...
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