Dual Voltage Power Supply

Dual Voltage Power Supply
author: YMYA electronics - IZHAR FAREED
Description
The following circuit Diagram of (DUAL VOLTAGE POWER SUPPLY ) can be used for Misc.. application.
It requires a few components to built. The most important components of this circuit are REGULATORS.
1 : (AN) 7812 and 2 : (AN) 7912 AN7812 is the Positive Voltage Regulator. It regulates the voltage from (almost) 24vDC to 12vDC (accurate). AN7912 is the Negative Voltage Regulator. It regulates the voltage from (almost) -24vDC to -12vDC. A transformer output must be between 12vAC to 24vAC @ 500mA. Input of transformer (Primary)
should be about 110vAc-220vAC. It also include some capacitors to filter the current.

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Source: Dual Voltage Power Supply

5 Lamp / LED Flash Driver

5 Lamp / LED Flash Driver
author: Rajkumar Sharma

Description

General Description of the following circuit. This circuit is based around HT2050 manufactured by HOLTEK semiconductors. It is a low cost, low-power C-MOS LSI designed for lamp andLED flash driver. It requires minimum external components.You can operate it with just two AAA cell or 3v Battery.Circuit has five flash outputs with 10mA drive capability that can implement random or sequence flashing function controlled by one option pin.It only requires one external resistor for typical application. It is very suitable for the use of the flash products such as disco glasses, disco hat, gift card, Xmas decoration and so forth.

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Source: 5 Lamp / LED Flash Driver

20W Bridge Audio Amplifier

20W Bridge Audio Amplifier
author: Rajkumar Sharma

Specifications

20W Bridge Audio Amplifier kit, based on the TDA2005 IC, a class B dual audio amplifier, specifically designed for car radio applications etc. Power supply - 18 VDC Output power - 20 W, 4 Ω IC built in Thermal Shut-down, Load dump voltage surge protected Terminal pins for connecting left and right audio signal inputs Relimate Connector for connecting Potentiometer (POT) for volume adjustment Power Battery Terminal (PBT) for easy power supply and speaker connection Power-On LED indicator Heatsink for IC Four mounting holes of 3.2 mm each with nut and stud PCB dimensions 63 mm x 65 mm

Schematic

Parts List

PCB

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Source: 20W Bridge Audio Amplifier

Notch Filter

Notch Filter
Circuit : Andy Collinson
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Description:

A variable notch filter with both high and low pass filters.

Notes

At first glance this circuit looks fairly complex, but when broken down,can be divided into high pass and low pass filter sections followed by a summing amplifier with a gain of around 20 times. Supply rail voltage is +/- 9V DC. The controls may also be adjusted for use as a band stop (notch) filter or band pass filter.
Source: http://www.zen22142.zen.co.uk

Stereo Line Driver

Circuit : Andy Collinson
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Description:

A stereo line driver for feeding long cables or buffering an audio source.

Notes

This preamplifier has a low output impedance, and is designed to drive long cables, allowing you to listen to a remote music source without having to buy expensive screened cables. The very low output impedance of around 16 ohms at 1KHz, makes it possible to use ordinary bell wire,loudspeaker or alarm cable for connection. The preamplifier must be placed near the remote music source, for example a CD player. The cable is then run to a remote location where you want to listen. The output of this preamp has a gain of slightly less than one, so an external amplifier must be used to drive loudspeakers.
Source: http://www.zen22142.zen.co.uk

Voltage Follower Circuit

Two examples of the most common types of Voltage followers (buffers). You can find some theory behind them in our amplifier gain and buffer amplifier pages.

Transistor voltage follower:

This first circuit is a very simple one transistor voltage follower. Consist of two biasing resistors, and one other resistor at the emitter to acquire the output voltage from.

How it works:

The first to resistors connected to the transistor's base are forming a voltage divider, in order to set a biasing point for the transistor to work in our desired range. Then the transistor, our gain component for the circuit which in this case is only used as a gateway to isolate two circuit stages.

The resistor in the emitter is used to create a voltage from the current passing from the transistor; Without it we can't get any voltage as our output would be effectively shorted to ground (0 volts).

The capacitors that are displayed in the schematic are optional, but very useful to prevent a wrong operation of the circuit, specially in audio or high frequency uses. they stop any DC voltage to move or otherwise disrupt the bias point of the transistor, thus causing undesired operation. If you build this circuit only with dc remove the capacitors, as they will prevent the circuit from functioning under those conditions.

Transistor voltage follower

Op Amp Voltage Follower:

This circuit's operation is far more predictable and stable than the transistor version, and also requires less external components.

How it works:

Works as described above, no external elements to explain. This circuit uses feedback to maintain the voltage output the same as the input. Note that this schematic does not display power, ground and other connections for the op amp, these vary widely among manufacturers and op amps so refer to your op amp's datasheet for pinouts and power connections.
Opamp voltage follower
Source: Electronic Circuits For Beginners

5 Zone Alarm System

Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk Description
This is a complete alarm system with 5 independent zones suitable for a small office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a "system armed" indicator. The schematic is as follows:
Circuit Notes:
Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Suitable switches can be bought from alarm shops and concealed in door frames, or window ledges.

Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppresser. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key.
Operation:
At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Source:www.zen22142.zen.co.uk

Emergency Light & Alarm

Powered by two AA NI-CD batteries

Four switchable options

Parts:

R1____________220K   1/4W Resistor
R2____________470R   1/2W Resistor
R3____________390R   1/4W Resistor
R4______________1K5  1/4W Resistor
R5______________1R   1/4W Resistor
R6_____________10K   1/4W Resistor
R7____________330K   1/4W Resistor
R8____________470R   1/4W Resistor
R9____________100R   1/4W Resistor

C1____________330nF  400V Polyester Capacitor
C2_____________10µF   63V Electrolytic Capacitor
C3____________100nF   63V Polyester Capacitor
C4_____________10nF   63V Polyester Capacitor

D1-D5________1N4007 1000V 1A Diodes
D6______________LED  Green (any shape)
D7___________1N4148   75V 150mA Diode

Q1,Q3,Q4______BC547   45V 100mA NPN Transistors
Q2,Q5_________BC327   45V 800mA PNP Transistors

SW1,SW2________SPST Switches
SW3____________SPDT Switch

LP1____________2.2V or 2.5V 250-300mA Torch Lamp

SPKR___________8 Ohm Loudspeaker

B1_____________2.5V Battery (two AA NI-CD rechargeable cells wired in series)

PL1____________Male Mains plug

Device purpose:

This circuit is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen.
When power supply is restored, the lamp or the alarm is switched-off. A switch provides a "latch-up" function, in order to extend lamp or alarm operation even when power is restored.

Circuit operation:

Mains voltage is reduced to about 12V DC at C2's terminals, by means of the reactance of C1 and the diode bridge (D1-D4). Thus avoids the use of a mains transformer.
Trickle-charging current for the battery B1 is provided by the series resistor R3, D5 and the green LED D6 that also monitors the presence of mains supply and correct battery charging.
Q2 & Q3 form a self-latching pair that start operating when a power outage occurs. In this case, Q1 biasing becomes positive, so this transistor turns on the self latching pair.
If SW3 is set as shown in the circuit diagram, the lamp illuminates via SW2, which is normally closed; if set the other way, a square wave audio frequency generator formed by Q4, Q5 and related components is activated, driving the loudspeaker.
If SW1 is left open, when mains supply is restored the lamp or the alarm continue to operate. They can be disabled by opening the main on-off switch SW2.
If SW1 is closed, restoration of the mains supply terminates lamp or alarm operation, by applying a positive bias to the Base of Q2.

Notes:

• Close SW2 after the circuit is plugged.

• Warning! The circuit is connected to 220Vac mains, then some parts in the circuit board are subjected to lethal potential!. Avoid touching the circuit when plugged and enclose it in a plastic box.

This circuit was awarded with publication in ELECTRONICS WORLD "Circuit Ideas", September 2001 issue, page 708.

Source : http://english.cxem.net/guard/guard17.php