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Showing posts with label automatic. Show all posts

Friday, April 5, 2013

Make this Automatic 10 Watt to 1000 Watt LED Emergency Light Circuit

The following post explains a very simple yet an outstanding automatic 1 watt to 1000 watt emergency lamp circuit. The circuit also includes an automatic over voltage and low voltage battery shut off feature.

The entire circuit functioning may be understood with the following points:

Referring the below given circuit diagram, the transformer, bridge and the associated 100uF/25V capacitor forms a standard step down AC to DC power supply circuit.

The bottom SPDT relay is directly connected with the above power supply output such that it remains activated when mains is connected with the circuit.

In the above situation, the N/O contacts of the relay stay connected which keeps the LED shut OFF (since its connected with the N/C of the relay).

This takes care of the LED switching, making sure than the LEDs are switched ON only in the absence of mains power.

However, the positive from the battery is not directly connected with the LED module, rather it comes via another relay N/O contacts (the upper relay). This relay is integrated with a high/low voltage sensor circuit stationed for detecting the battery voltage conditions.

Supposing the battery is in a discharged condition, switching ON the mains keeps the relay deactivated so that the the rectified DC can reach the battery via the upper relay N/C contacts initiating the charging process of the connected battery.

When the battery voltages reaches the "full charge" potential, as per the setting of the 10 K preset, the relay trips and joins with the battery through its N/O contacts.

Now in the above situation if the mains fails, the LED module is able to get powered via the above relay and the lower relay N/O contacts and get illuminated.

Since relays are used, the power handling capacity becomes sufficiently high. The circuit is thus able to support in excess of 1000 watts of power (lamp), provided the relay contacts are appropriately rated for the preferred load.

Tuesday, April 2, 2013

Simple Automatic Switch For Audio Power Amplifier

Circuit of an automatic switch for audio power amplifier stage is presented here. The circuit uses stereo preamplifier output to detect the presence of audio to switch the audio power amplifier on only when audio is present. The circuit thus helps curtail power wastage. IC1 is used as an inverting adder. The input signals from left and right channels are combined to form a common signal for IC2, which is used as an open loop comparator. IC3 (NE556) is a dual timer. Its second section, i.e., IC3(b), is configured as monostable multivibrator. Output of IC3(b) is used to switch the power amplifier on or off through a Darlington pair formed by transistors T1 and T2. IC3(a) is used to trigger the monostable multivibrator whenever an input signal is sensed.

Circuit diagram:

Automatic Switch For Audio Power Amplifier Circuit Diagram

Under ‘no signal’ condition, pin 3 of IC2 is negative with respect to its pin 2. Hence the output of IC2 is low and as a result output of IC3(a) is high. Since there is no trigger at pin 8 of IC3(b), the output of IC3(b) will be low and the amplifier will be off. When an input singal is applied to IC1, IC2 converts the inverted sum of the input signals into a rectangular waveform by comparing it with a constant voltage which can be controlled by varying potentiometer VR1. When the output of IC2 is high, output pin 5 of IC3 goes low, thus triggering the monostable multivibrator. As soon as the audio input to IC1 stops, pin 5 of IC3 goes high and pin 1 of IC3 discharges through capacitor C3, thus resetting the monostable multivibrator.

Hence, as long as input signals are applied, the amplifier remains ‘on.’ When the input signals are removed, i.e., when signal level is zero, the amplifier switches off after the mono flip-flop delay period determined by the values of resistor R8 and capacitor C3. If no input signals are sensed within this time, the amplifier turns off—else it remains on. Power supply for the circuit can be obtained from the power supply of the amplifier. Hence, the circuit can be permanently fitted in the amplifier box itself. The main switch of the amplifier should be always kept on. Resistors R1 and R2 are used to divide single voltage supply into two equal parts.

Capacitors C1 and C2 are used as regulators and also as an AC bypass for input signals. Diode D1 is used so that loading fluctuations in power amplifier do not affect circuit regulation. Transisitor T2 acts as a high voltage switch which may be replaced by any other high voltage switching transistor satisfying amplifier current requirements. Value of resistor R10 should be modified for large current requirement. The LED glows when the amplifier is on. The circuit is very useful and relieves one from putting the amplifier on and off every time one plays a cassette or radio etc.

http://streampowers.blogspot.com/2012/06/simple-automatic-switch-for-audio-power_11.html

Monday, April 1, 2013

Automatic Mains Disconnect Circuit

Downloading and CD-burning programs usually provide the option of automatically shutting down the PC on completion of their tasks. However, this energy-saving feature is of little beneﬁt if even after the PC has been switched off, all of the peripheral equipment remains connected to the mains and happily consumes watt-hours. The circuit shown here provides a solution to this dilemma. It is connected ahead of the power strip and connects or disconnects mains power for all of the equipment via a power relay. A connection to a 12-V PC fan (which may be the processor fan or the fan for the chipset, if the latter is present) indicates whether the PC is switched on.

If you are certain that the 12-V power supply voltage is switched off when the PC is in the sleep mode, you can use this connection instead. To switch everything on, press the Start button to cause the power relay to be energized and provide mains voltage to all of the equipment. If the PC has an ATX board, its Power switch must be pressed at the same time to cause the PC to start up. When the PC fan starts to run, low-power relay Re1 engages and takes over the function of the Start switch, which can then be released. This state is stable. If the PC switches to the sleep state, the 12-V voltage drops out.

Automatic_Mains_Disconnect

The electrolytic capacitor ensures that Re1 remains engaged for a short time, after which it drops out, followed by the power relay. D1 prevents the electrolytic capacitor from discharging through the connected fan, and D2 is the usual freewheeling diode. The system is disconnected from both mains leads and is thus completely de-energized. Be sure to select components that are suitable for their tasks. Naturally, the contacts of Re2 should be rated to handle the total current drawn by all of the peripheral equipment and the PC, and the relay coil must be suitable for use with mains voltage (6 mm minimum separation between coil and contacts).

A low-power 12-V relay that can switch mains voltage is adequate for Re2. The Start pushbutton switch is connected to the mains voltage, so a 230-V type must be used. The circuit board layout and enclosure must also be designed in accordance with safety regulations. A separation of at least 6 mm must be maintained between all components carrying mains voltage and the low-voltage components, and the enclosure must be completely free of risk of electrical shock. With a bit of skill, the circuit can be ﬁtted into a power bar with a built-in switch, if the switch is replaced by a pushbutton switch having the same mounting dimensions.

Note:

The circuit is not suitable for use with deskjet printers that can only be switched on and off by a front panel button.

Source : www.extremecircuits.net

Saturday, March 30, 2013

Automatic TV Lighting Switch

The author is the happy owner of a television set with built-in Ambilight lighting in the living room. Unfortunately, the television set in the bedroom lacks this feature. To make up for this, the author attached a small lamp to the wall to provide background lighting, This makes watching television a good deal more enjoyable, but it ’s not the ideal solution. Although the TV set can be switched off with the remote control, you still have to get out of bed to switch off the lamp.

Automatic TV Lighting Switch Circuit diagram:

Consequently, the author devised this automatic lighting switch that switches the background light on and off along with the T V set. The entire circuit is fitted in series with the mains cable of the TV set, so there’s no need to tinker with the set. It works as follows: R1 senses the current drawn by the TV set. It has a maximum value of 50 mA in standby mode, rising to around 500 m A when the set is operating. The voltage across R1 is limited by D5 during negative half- cycles and by D1– D4 during positive half-cycles. T he voltage across these four diodes charges capacitor C1 via D6 during positive half-cycles. This voltage drives the internal LED of solid-state switch TRI1 via R2, which causes the internal triac to conduct and pass the mains voltage to the lamp. Diode D7 is not absolutely necessary, but it is recommended because the LED in the solid-state switch is not especially robust and cannot handle reverse polarisation. Fuse F1 protects the solid-state switch against overloads. T he value of use d here (10 Ω) for resistor R1 works nicely with an 82-cm (32 inch) LCD screen.

With smaller sets having lower power consumption, the value of R1 can be increased to 22 or 33 Ω, in which case you should use a 3-watt type. Avoid using an excessively high resistance, as otherwise TRI1 will switch on when the TV set is in standby mode. Some TV sets have a half-wave rectifier in the power supply, which places an unbalanced load on the AC power outlet. If the set only draws current on negative half-cycles, the cir-cuit won’t work properly. In countries with reversible AC power plugs you can correct the problem by simply reversing the plug. Compared with normal triacs, optically cou-pled solid-state relays have poor resistance to high switch-on currents (inrush currents).

For this reason, you should be careful with older-model TV sets with picture tubes (due to demagnetisation circuits). If the relay fails, it usually fails shorted, with the result that the TV background light remains on all the time. If you build this circuit on a piece of perf-board, you must remove all the copper next to conductors and components carrying mains voltage. Use PCB terminal blocks with a spacing of 7.5 mm. This way the separation between the connections on the solder side will also be 3 mm. If you fit the entire arrangement as a Class II device, all parts of the circuit at mains potential must have a separation of at least 6 mm from any metal enclosure or electrically conductive exterior parts that can be touched.

Author :Piet Germing - Copyright : Elektor

Source : http://www.ecircuitslab.com/2012/03/automatic-tv-lighting-switch.html