Voltage Controlled Switch using 555 Timer descroption and circuit

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 cant compete with. (This high impedance input must not be left open.) A large hysteresis makes the circuit immune to noise. The output (pin 3) can only be either high or low (voltage-wise), and it changes its state almost instantenously, regardless of the input signal shape.

The voltage drop across the NE555s output stage (at 35-100 mA) is 0.3-2.0 V, depending on the way the relay is connected and the exact current it draws. D1 is absolutely vital to the safety of the integrated circuit.Source :: http://www.zen22142.zen.co.uk/Circuits/Switching/vcs555.htm
Read More

SOFT START MECHANISM FOR L200 VOLTAGE REGULATOR ELECTRONIC DIAGRAM

SOFT START MECHANISM FOR L200 VOLTAGE REGULATOR ELECTRONIC DIAGRAM

Ic (constant current) is charge capacitor C, where Ic = Vsc/R.

The output reaches its nominal value after the time ton. Vo-Vsc=(Ic.ton)/C.

ton=C.[(Vo-0.45)/0.45].R = CVoR/0.45.

Vo follows the voltage in pin 2 at less than 0.45 volt. It is because voltage of more than 0.45 V can’t be produced between pin 2 and pin 5. Read More

Mains Emergency Voltage Cut Out Circuit for Computers

 lf the voltage of the mains supply of a computer rises too high, components on the printed circuit boards can easily be damaged or even destroyed.

This emergency cutout placed between the mains supply and the load interrupts the supply when the voltage level exceeds a predetermined value. . For many reasons it is possible for the output voltage of a power supply to rise to a dangerous level. The emergency cutout described here has been set to the maximum supply voltage of 5.25 V that is stated by the manufacturers of TTL ICs. Zener diode D1 starts conducting just before the stated zener voltage is reached. A small current flows in the and gate circuit of thryristor Th1; the level of this current can be set with preset potentiometer P1 connected in parallel with the gate cathode circuit of Th1. When the mains supply rises, the current ’through the zener diode becomes large enough to cause the thyristor to fire. The firing level lies between 5.2 . . . 6 V. As soon as the thyristor fires, the mains supply voltage drops substantially because the thyristor virtually short-circuits the mains supply. ln the case of a supply without current limiting, fuse F1 prevents the current attaining too high a value.

The rating of the fuse depends, of course, on the load requirement. During testing and adjusting of the circuit, it is important that the thyristor continues to conduct after it has been fired until its current has dropped to zero. The firing voltage level can be set by means of a mains supply with a current limiter before it is put into use, lf it proves impossible, for instance because of tolerances of the zener diode, to set the firing voltage to the required value, try using a 5.1 V zener diode.

If the voltage of the mains supply of a computer rises too high, components on the printed circuit boards can easily be damaged or even destroyed. This emergency cut-out placed between the mains supply and the load interrupts the supply when the voltage level exceeds a predetermined value.

For many reasons it is possible for the output voltage of a power supply to rise to a dangerous level. The emergency cut-out described here has been set to the maximum supply voltage of 5.25 V that is stated by the manufacturers of TTL ICs. Zener diode D1 starts conducting just before the stated zener voltage is reached. A small current flows in the anode-gate circuit of thryristor Th1.

The level of this current can be set with preset potentiometer P1 connected in parallel with the gate-cathode circuit of Th1. When the mains supply rises, the current through the zener diode becomes large enough to cause the thyristor to fire. The firing level lies between 5.2 . . 6 V.

As soon as the thyristor fires, the mains supply voltage drops substantially because the thyristor virtually short-circuits the mains supply. In the case of a supply without current limiting, fuse F1 prevents the current attaining too high a value.

The rating of the fuse depends, of course, on the load requirement. During testing and adjusting of the circuit, it is important that the thyristor continues to conduct after it has been fired until its current has dropped to zero. The firing voltage level can be set by means of a mains supply with a current limiter before it is put into use. If it proves impossible, for instance because of the tolerances of the zener diode to set the firing voltage to the required value, try using a 5.1 V zener diode.
Circuit Description

Referring to the given circuit diagram of a simple DC short circuit protector for computers, the functioning may be grasped with the following points:

The zener diode along with R1 and P1 forms a voltage reference or threshold level for the thyristor gate which is connected at the the center of the above network.

P1 is adjusted to the desired threshold level at which the thyristor is required to be fired.

As long as the input voltage stays below this set level the thyristor remains inactive and the supply output to the computer undergoes a normal execution.

However if the input voltage tends to drift above the set level, the gate potential of the thyristor reaches the firing point and it fires, shorting the voltage across the output to ground.

The above action instantly drops the voltage to the safe set threshold so that now the thyristor is switched OFF.

The above triggering continues as long as the input voltage stays above the threshold mark, thus rectifying the output voltage to the safe limit, ensuring the computer a safe operating environment.

Read More

Mains Voltage Detector

The detector is intended to sense and signal to another circuit that an appliance is connected to the mains voltage. For this purpose, an optocoupler, IC1 in the circuit, is used. The light-emitting diode in this device is connected across the mains voltage rectified by bridge B1. The mains voltage is applied to this bridge via potential divider R1-C1-R2. When the capacitor has a value as specified in the diagram, the current through the diode is about 700 µA (for a mains voltage of 230 V). This results in sufficient light to make the photo-transistor conduct. The drop across the LED is about 1V.


The detector draws a current only when the monitored equipment is switched on. It is intended to be built into the appliance whose mains connection is to be monitored and must, of course, be connected behind the mains on/off switch. A possible application of the detector is in the preamplifier described in this blog (‘DIY: From vinyl to compact disc’). When it senses that the record player is being switched on, it can be used to link the Line-In input of the soundcard automatically to the preamplifier. Another possible application is its use as a power-on reset circuit in a protection system.


Transistor T1 can switch currents of up to 10mA; in the prototype, the knee voltage of the transistor was around 200mV at a current of 20mA. The maximum permissible switching voltage of the optocoupler is 30 V. Fuse F1 is added to allow a fuse to be omitted on the monitored appliance.


Resistors:

• R1,R2 = 100Ω
• R3 = 100kΩ
• Capacitors:
• C1 = 10nF 250VAC (class X2)
• C2 = 47µF 25V radial

Semiconductors:

• B1 = B250C1500
• T1 = BC547B
• IC1 = CNY65

Miscellaneous:

• K1,K2 = 2-way PCB terminal block, pitch 7.5mm
• F1 = fuse holder with fuse (rated as required)
  

Read More

Delay and Music Power Supply Circuit with High and Low Voltage

Delay and Music Power Supply Circuit with High and Low Voltage

Voltage variations and ability cuts abnormally affect assorted equip- ment such as TVs, VCRs, music systems and refrigerators. This simple ambit will assure the cher accessories from aerial as able-bodied as low voltages and the voltage surges (when ability resumes). It additionally gives a accordant tune back mains ability resumes. Back mains voltage is normal, the DC voltage at the cathode of zener diode D4 is beneath afresh 5.6V. As a aftereffect transistor T1 is in off state. The DC voltage at the cathode of zener diode D5 is greater than 5.6V and as a aftereffect transistor T2 is in on state. Consequently, broadcast RL1 gets energised, which is adumbrated by lighting up of blooming LED. Under aerial mains voltage condition, transistor T1 switches to on accompaniment because the voltage at cathode of zener diode D4 becomes greater than 5.6V. Consequently, transistor T2 switches to off state, authoritative the broadcast to de-energise Under low mains voltage condition, transistor T1 switches to off accompaniment and as a aftereffect transistor T2 additionally switches to off state, authoritative the broadcast to de-energise.

Timer IC 555 in the ambit is configured to accomplish in a monostable mode. The beating amplitude is about 10 abnormal with the timing basic ethics acclimated in the schema. Back the ability resumes afterwards a break, pin 2 of IC 555 goes low briefly and this triggers it. Its achievement makes music IC UM66 to accomplish through transistor T3. Simultaneously, transistor T1 additionally gets advanced biased as the monostable IC1 achievement is affiliated to its abject via diode D8 and resistor R7. As a result, transistor T1 conducts and biases transistor T2 to cut off. Thus broadcast RL1 charcoal de-energised for the continuance of address beating and the amount is adequate adjoin the voltage surges.

To acclimatize presets VR1 and VR2, you may use a manually capricious auto-transformer. Set the achievement of auto-transformer to 270V AC and affix it to the primary of agent X1. Acclimatize preset VR1 such that broadcast RL1 aloof de-energises. Next set the achievement of auto-transformer to 170V AC. Now acclimatize preset VR2 such that broadcast RL1 afresh de-energises. Aggregate ascendancy VR3 may be adapted for the adapted achievement aggregate of the tune generated by IC UM66

Read More

Automotive Voltage Indicator

Connecting this schema to the battery of your vehicle, you will always know at a glance the approximate voltage available.An indication of battery voltage is useful to the motorist for monitoring the batterys capacity to deliver current, and as a check on the efficiency of the dynamo or alternator.Threshold voltages of the LEDs are set by means of two Zener Diodes (D6 & D10) plus two further Diodes wired in series (D4, D5 and D8, D9 respectively) adding a step of about 1.3V to the nominal Zener voltage.








Parts:
R1,R3,R6________1K 1/4W Resistors
R2____________100K 1/4W Resistor
R4,R5,R7,R8_____3K3 1/4W Resistors
D1__________Red LED (Any dimension and shape)
D2________Amber LED (Any dimension and shape)
D3,D4,D5_____1N4148 75V 150mA Diodes
D6_________BZX79C10 10V 500mW Zener Diode
D7________Green LED (Any dimension and shape)
D8,D9________1N4148 75V 150mA Diodes
D10________BZX79C12 12V 500mW Zener Diode
Q1,Q2_________BC547 45V 100mA NPN Transistors
Q3____________BC557 45V 100mA PNP Transistor



LED indication:
* Red LED D1 is on when battery voltage is 11.5V or less. This indicates a low battery charge. * Amber LED D2 is on when battery voltage is comprised in the 11.5 - 13.5V range. This indicates that the battery is good if the motor is off. When motor is running, this indicates no charge from dynamo or alternator. * Green LED D7 is on when battery voltage is 13.5V or more. This indicates a normal condition when motor is running and dynamo or alternator are charging.

Read More

Build a High Voltage Inverter Wiring diagram Schematic

The High Voltage Inverter Circuit Diagram converts a de voltage (V +) to a high-amplitude square wave in the audio-frequency range. The dual timer, IC2, provides an inexpensive alternative to the traditional transformer for providing complementary base drive to the power transistors, Ql and Q2. You can convert a 6 to 12 V battery output, for example, to an ac amplitude, which is limited primarily by the power rating of transformer Tl. 

Connect timer IC1 as an oscillator to provide a symmetrical square-wave drive to both inputs of IC2. The timing components, R2 and Cl, produce a 2.2-kHz output frequency. By connecting half of IC2 in the inverting mode and the other half in noninverting mode, the timer`s outputs alternately drive the two transistors. 

 Build a High Voltage Inverter Circuit Diagram

You can operate the audio-output transformer, Tl, as a step-up transformer by connecting it backwards using the output winding as an input. The transformer delivers an output voltage across RL of 4 x N x V+V pk-pk, where Nis the transformer turns ratio. For the schema shown, the output swing is 100 x V+V pk-pk.

Read More

Low Voltage Cut Out

Low Voltage Cut-Out Circuit diagram. This schema will detect when the voltage of a 12v battery reaches a low level. This is to prevent deep-discharge or maybe to prevent a vehicle battery becoming discharged  to a point where it will not start a vehicle. This schema is different to anything previously presented. It has HYSTERESIS. Hysteresis is a feature where the upper and lower detection-points are separated by a gap. 

Low Voltage Cut-Out Circuit diagram :

Low Voltage Cut-Out Circuit Diagram

Normally,  the schema will deactivate the relay when the voltage is 10v and when the load is removed. The battery voltage will rise slightly by as little as 50mV and turn the schema ON again. This is called "Hunting." The off/on timing has been reduced by adding the 100u. But to prevent this totally from occurring, a 10R to 47R is placed in the emitter lead. The schema will turn off at 10v but will not turn back on until 10.6v when a 33R is in the emitter. The value of this resistor and the turn-on and turn-off voltages will also depend on the resistance of the relay. 

Author : Colin Michel - Copyright : 200 Transistor Circuits

Read More

Pre regulated High Voltage Power Supply Wiring diagram Schematic

This Pre-regulated High Voltage Power Supply Circuit Diagram triacs selects the tap on main transformer Tl, which provides the proper, pre-regulated voltage to the secondary regulator. T2 and its associated components comprise the secondary regulator. The ADC 0804, IC1, digitizes a voltage-feedback signal from the secondary regulator`s output. 

 Pre-regulated High Voltage Power Supply Circuit Diagram

The MC1415 De-multiplexer, IC2, decodes the digitizer`s output. IC2, in turn, drives Tl`s opto-isolated triacs via the 74LS240 driver chip, IC3, and associated opto-isolators. Transformer T3 samples the schema`s current output. The auxiliary, 12 V winding on Tl ensures noload starting. The combination of op amp IC5 and the inverting transistor, Ql, square this current signal. 

The output of Ql is the CLK signal, which triggers one-half of the one shot, IC4A, to begin the schema`s AID conversion. The one shots` periods are set to time out within 1l2 cycle of the ac input. Upon completion of its AID conversion, ICl`s INTR output triggers the other half of the one shot, IC4B, which enables the converter`s data outputs. The rising edge of the CLK signal resets the one shot and latches the new conversion value into IC2. The latch, associated driver, and optoisolator trigger a selected triac according to the latest value of the voltage-feedback signal, V, . Keep enjoying dont forget click on share button .

Read More

Under voltage indicator Wiring diagram Schematic

Under voltage indicator Circuit Diagram as use for battery equipment. This is a meter counter schema in this schema due to the low duty cycle of flashing LED, the average current drain is 1 mA or less. The NE555 will trigger the LED on when the monitored voltage falls to 12 volts The ratio of Rl to R2 only needs to he changed if it is desired to change the voltage point at which the LED is triggered.

Under voltage indicator Circuit Diagram

Sourcd By : Circuitsstream

Read More

NE555 Voltage doubler circuit

The circuit diagram of a absolute simple voltage doubler application NE555 timer is apparent here. Actuality IC NE555 is active as an astable mutivibrator operating at about 9KHz. The abject of the two transistors (Q1 and Q2) is shorted and achievement of the astable multivibrator (pin 3) is affiliated to it.

When the achievement of astable multivibrator is low, Q1 will be OFF and Q2 will be ON. The abrogating terminal of the capacitor C3 will be shorted to arena through T2 and it will be answerable to the ascribe accumulation voltage. When the achievement of the astable multi vibrator is high, transistor Q1 will be ON and transistor Q2 will be OFF. The capacitor C4 will be answerable to the voltage beyond capacitor C3 additional the ascribe accumulation voltage. This is how the circuit works.

This voltage doubler circuit can bear alone up to 50mA achievement accepted and aloft that accepted absolute the achievement voltage will be badly reduced. The absolute achievement voltage will be about 19V for a 12V DC ascribe and aswell the achievement voltage will be a bit unstable. Anyway, for low accepted applications this circuit is able-bodied enough.

Read More