Emergency Laptop Charger

Emergency Laptop Charger means a true-portable circuit to charge Laptop computer from a commonly available power supply source.Described here is a simple circuit to charge laptop computer from any 12V car battery.This circuit can be connected to the cigar-lighter socket of the car to produce clean and stable DC supply of near 19V/5A,from the 12V battery supply.Enough and more for many laptops!

The circuit,from Elektor Electronics (UK), is built around the ubiquitous IC UC 3843 (IC1),from Fairchild (http://www.fairchildsemi.com/). The UC3843 is a fixed frequency current-mode PWM controller,specially designed for Off-Line and DC to DC converter applications with minimum external components. This IC features a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator and a high current totempole output for driving a Power MOSFET.

Features of UC3843

• Low Start up Current

• Maximum Duty Clamp

• UVLO With Hysteresis

• Operating Frequency up to 500KHz

In this circuit IRL2505 (T1) power mosfet is used as the inductor driver.IRL 2505,the Fifth Generation HEXFET from International Rectifier (http://www.irf.com/)  utilize advanced processing techniques to achieve extremely low on-resistance per silicon area.

Features of IRL2505

• Advanced Process Technology
• Ultra Low On-Resistance
• Dynamic dv/dt Rating
• 175°C Operating Temperature
• Fast Switching
• Fully Avalanche Rated
• Logic-Level Gate Drive

Another major component is the 56uH power inductor.A preset-pot (P1) is added here to "fine tune" the output volatge level.After construction on a suitable piece of veroboard,enclose the whole circuit in an attractive and convenient plastic/metal box of your choice.

Automatic Garden/Lawn light

Ultra simple and economical circuit of an automatic garden/lawn light is presented here.This compact circuit is built around common,inexpenxive and easy to use electronic components.This circuit is basically a 230VAC mains operated white LED lighting unit with built in twilight sensor mechanism.

Working of the circuit is straight forward.AC 230V supply available across the input of the circuit is down-convereted to a safe and steady value of near 7.5 VDC by the series drop capacitor - behaves as a voltage dropping ‘resistor’ - (C1),half-wave rectifier (D1),zener diode (ZD1) and the buffer capacitor (C2).This method is cheaper and smaller compared to using a step-down transformer.This DC supply is fed to the gate terminal of the lamp control triac (T2) through a medium-power driver transistor (T1).In normal condition,ie if the ambient light level is more than the threshold value set by the sensitivity control trimpot (VR1),T1 is reverse biased by the light detector (LDR) and the triac remains in off state.

In case of darkness, state of T1 is reversed to fire the triac and as a result input ac supply is routed to the bridge rectifier assembly (D2-D5) through the triac.This brige rectifier unit converts the high voltage ac supply to a low value dc supply with the help of the second series drop capacitor (C3).Here 15 standard white LEDS (LED 1 - LED 15) - wired in series - are connected across a buffer capacitor (C4).Buffer capcitor (C4) ensures that there is sufficient voltage to light the LEDs when the available mains voltage is less than the forward voltage of the LEDs and it takes care of the surge that occurs when the mains is switched on.This current pulse could otherwise damage the LED string.Resistor R3 limits the operating current of the LED string.