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Voltage stabilizers are used for  many appliances in homes,  offices and industries. The  mains supply suffers from large voltage  drops due to losses on the distribution  lines en route. A voltage stabilizer  maintains the voltage to the appliance  at the nominal value of around 220  volts even if the input mains fluctuates  over a wide range. Here is the circuit of an automatic  voltage stabilizer that can be adapted  to any power rating. Its intelligence  lies in the program on PIC16F877A—a  low-cost microcontroller that is readily  available. The circuit, when used with  any appliance, will maintain the voltage  at around 220V even if the input  mains voltage varies between 180V  and 250V. Here the circuit is shown for a  5A stabilizer. It acts within 100ms to  produce a smoothly varying output  whenever input mains voltage changes.  (Servo stabilizers move a variable...

Continuous monitoring of the mains voltage is required in many ap-plications such as manual volt-age stabilisers and motor pumps. An ana-logue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-pur-pose analogue voltmeter. The status of the mains voltage is available in the form of an LED bar graph. Presets VR1 through VR16 are used to set the DC voltages corresponding to the 16 voltage levels over the 50-250V range as marked on LED1 through LED16, respectively, in the figure. The LED bar graph is multiplexed from the bottom to the top with the help of ICs CD4067B (16-channel multiplexer) and CD4029B (counter). The counter clocked by NE555 timer-based astable multivibrator generates 4-bit binary ad-dress for multiplexer-demultiplexer pair of CD4067B and CD4514B. Circuit diagram: Digital Mains Voltag...

A voltage regulator is used to produce a constant linear output voltage. It’s generally used with AC to DC power supply. And also it can be used as well as a DC to DC voltage converter . To regulating low voltage, most used device is one single IC. 7805, 7812, 7905 etc. 78xx series are design for positive and 79xx series are for Negative voltage regulator. 7805 is a three terminal +5v voltage regulator IC from 78XX chips family. See 7805 pinout below. LM78XX series are from National Semiconductor. They are linear positive voltage regulator IC; used to produce a fixed linear stable output voltage.  National Semiconductor has also negative voltage regulator chips family, they indicate with LM 79XX. 78xx is used more than 79xx because negative voltage has a few usability purposes as we see. I was previously posted a 5v regulated power supply circuit using 7805 IC , that circuit and this 7805 voltage regulator circuit is almost the same. 7805 Voltage Regulator Circuit Diagram ...

This electronic voltage controlled switch circuit diagram project make a very easy. In this electronic project circuit the 555 timer is used in a novel way, as a voltage controlled switch.  Voltage Controlled Switch Circuit Diagram: Notes: The old and omnipresent NE555 can be very good at something it was not meant for: driving relays or other loads up to 200 mA. The picture shows an example circuit: if the input level rises over 2/3 of the supply voltage - it will turn on the relay, and the relay will stay on until the level at the input drops below one third of the supply voltage. If the relay and D1 were connected between pin 3 and ground, the relay would be activated when the input voltage drops below one third, and deactivated when the input voltage goes over two thirds of the supply voltage. It is also a nice advantage that the input requires only about 1 uA, which is something bipolar transistors can't compete with. (This high impedance input must not be left open.) A large ...

Build a Voltage-Controlled Attenuator VC Using FET . Using the circuit shown in the schematic diagram below, we can control the low-level audio signals with ±3V variable DC voltage. This attenuator circuit uses a field effect transistor (FET) to shunt the signal to ground. The R2 is used to control the output level (the attenuation level), but you can use other source of voltage signal to control the grid of the FET, such as DAC output, just remember that this voltage is a negative going signal (you can use with DAC which uses symmetric power supply system). The minimum output of this circuit is when gate bias is zero. When the gate bias is set close to pinchoff value, the circuit will produce maximum output with value that equal to input level. Here is the schematic diagram of the circuit: Voltage-Controlled Attenuator VC Using FET Circuit Diagram

A simple 5 Volt regulated PSU featuring overvoltage protection. The 5 volt regulated power supply for TTL and 74LS series integrated circuits, has to be very precise and tolerant of voltage transients. These IC's are easily damaged by short voltage spikes. A fuse will blow when its current rating is exceeded, but requires several hundred milliseconds to respond. This circuit will react in a few microseconds, triggered when the output voltage exceeds the limit of the zener diode. This circuit uses the crowbar method, where a thyristor is employed and short circuits the supply, causing the fuse to blow. This will take place in a few microseconds or less, and so offers much greater protection than an ordinary fuse. Circuit diagram: Logic PSU With Over-Voltage Protection Circuit Diagram If the output voltage exceed 5.6Volt, then the zener diode will conduct, switching on the thyristor (all in a few microseconds), the output voltage is therefore reduced to 0 volts and sensitive logic IC...

This is the simple frequency voltage converter circuit diagram. Teledyne Semiconductor`s Type TSC9402 is a versatile IC. Not only can it convert voltage into frequency, but also frequency into voltage. It is thus eminently suitable for use in an add-on unit for measuring frequencies with a multimeter.  Only a few additional components are required for this.. Just one calibration point sets the center of the measuring range (or of that part of the range that is used most frequently). The frequency-proportional direct voltage at the output (pin 12—amp out) contains interference pulses at levels up to 0.7 V. If these have an adverse effect on the multimeter, they can be suppressed with the aid of a simple RC network.  The output voltage, U0, is calculated by: tfo=C/rei(Ci + 12 pF) R2fm Because the internal capacitance often has a greater value than the 12 pF taken here, the formula does not yield an absolute value. The circuit has a frequency range of dc to 10 kHz. At 10 kHz, t...

1.9 High voltage power lines and Lightning Electric accidents may occur to people even when they are not dealing directly with electricity. Two sources of such accidents are the high voltage power lines and lightning. High voltage power lines Two types of power lines are used: overhead power lines and underground power lines.  Overhead Power Line The power company distributes electricity throughout the country by overhead lines. The cables are not insulated. They are supported by tall posts called pylons to reduce the chances of people, animals and vegetation touching the bare conductors, since to do so may cause death. The following safety precautions should be observed in order to avoid accidents from overhead power lines: a.         Never attempt to climb electric power posts. b.        Do not touch broken overhead cables. Warn others about it and report to the authorities. c.       ...

This is the project of Voltage Monitor Circuit Diagram. This is a very simple circuit which can be modified to the user's needs. Its operation is simple, when the input voltage is 0, the LED (LO). The LED turns off when the voltage increases to the level determined by R2. Voltage Monitor Circuit Diagram

This voltage monitor is made to display the voltage of 12v battery (for UPS) on LEDs. For this purpose LM3914 is used. The voltage range decided to display is 10v to 13.5v for 12v battery. LM3914 is display driver that can be used in dot  mode or in bar mode; dot mode , with only one led is lit at a time, and in bar mode where it lights leds progressively when the voltage increases. The circuit needs to be powered from the battery being measured and to be able to adjust the lower and upper voltages that light the first and last leds on the led bar. For the 12V battery, the first led in the bar will lit at 10V and the last one at 13.5V , giving 0.35V per led. These thresholds may be set to other values by adjusting two trimmers in the circuit. Calculation and Adjustments: Current flowing per led is controlled by R3 resistor, by applying ohm's law  Ir3 =1.25v/ 4.7kohm =266uA.  Where 1.25v is the minimum voltage required to operate the led. To be able to read the supply vo...