variable voltage adjustable power supply circuits

Features:
Regulated Adjustable Voltage out 2-30VDC
High Current Output 5A (based on transformer selection).
Adjustable Current Limit
Can be used as a variable current supply.
Based on LM317 Voltage Regulator.
Built in protection diodes
Speed controlled fan connection (based on current draw).
Current meter connection (0.1V/1A).

                                                           Circuit Diagram

Features universal capcitor mounting/spacing to allow various capacitors to fit.  Mounting pattern that fits TO-200 or TO-218/247 for pass transistor and transistor used for current limit circuit.  Fan connection uses connection compatible with standard PC fan connection; allowing use of PC heatsink fan combination.

Circuit Board Layout
Electronics Circuit Application 

MOBILE PHONE BATTERY CHARGER CIRCUITS.

Mobile phone chargers available in the market are quite expensive. The circuit presented here comes as a low-cost alternative to charge mobile telephones/battery packs with a rating of 7.2 volts, such as Nokia 6110/6150.

 

12V to 220V inverte 500W Circuits

Attention: This Circuit is using high voltage that is lethal. Please take appropriate precautions

Using this circuit you can convert the 12V dc in to the 220V Ac. In this circuit 4047 is use to generate the square wave of 50hz and amplify the current and then amplify the voltage by using the step transformer.

 

AC Powered LED.

A long time ago I found a little schematic on internet on how to power a LED from an AC Line.
I tested and modified it a little so now it works great.
You could use it as an power-on indicator for your waterpump or so. Also it can be used with whatever LED-color you like.

I included the schematics for US or canadian 110-120V 60Hz AC lines, as well as european or australian 230-240V 50Hz AC lines.

The capacitor is used to drop the voltage and the resistor to limit the inrush current.
Since the capacitor passes the current in both directions, a small diode is connected in parallel with the LED to provide a path for the negative half cycle and to limit the reverse voltage across the LED. The resistor value was chosen to limit the worst case inrush current to about 150mA which will drop to less than 30mA in a millisec as the capacitor charges.
The 0.47uF capacitor has an impedance of 5600 Ohms at 60Hz so the LED current is about 20mA half wave, or 10mA average (for the 230V version the impedance of the 0.33uF capacitor is 9600 Ohms at 50Hz which gives you also a LED current of about 10mA average) 

Z = 1 / 2*Pi*f*C

Z = Impedance in Ohms

Pi = 3.14

f = frequency in Hertz

C = capacity in Farads)

A larger capacitor will increase the current and a smaller one will reduce it.
The capacitor must be a non-polarized type with a voltage rating of at least 250VDC or preferably more for 110V AC-lines, or at least 400VDC or preferably more for 230V AC-lines.
Resistor R1 discharges capacitor C1 in a few seconds after AC-line is disconnected. Remember that R1 must be able to withstand the full half wave peak AC-line voltage.
IMPORTANT: The circuit is powered from the AC line, so I will not be held responsible in any way for burned fingers, or melted fuses in your house. Isolate all connections with heat shrink.
Electronics Circuit Application

FM Transmitter Circuits - 4Transistors..

This circuit provides an FM modulated signal with an output power of around 500mW. The input microphone pre-amp is built around a couple of 2N3904 transistors (Q1/Q2), and audio gain is limited by the 5k preset trim potentiometer. The oscillator is a colpitt stage, frequency of oscillation governed by the tank circuit made from two 5pF ceramic capacitors and the L2 inductor. The output stage operates as a 'Class D' amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.Electronics Circuit Application

TV Transmitter Circuit ..

This is a small TV transmitter circuit which transmits in VHF band, negative sound modulation and PAL video modulation. It is suitable in countries where the B and G system is used. Electronics Circuit Application

High Gain Yagi Wi-Fi Antenna

Build this wi-fi antenna to build when you want results FAST and have just a few inexpensive tools and supplies available. It will greatly extend your wi-fi range - well beyond the limits of the dipoles that accompany most routers and some wireless adapters. When connected to a USB wireless adapter the performance is excellent. When connected to a high powered wi-fi adapter, the performance is astounding! Forget about building those overly hyped wi-fi cantennas - they don't perform anywhere close to the yagi antennas depicted here.
Sometimes the perfect wi-fi antenna is the one that can be made in an hour's time, from inexpensive parts, and yet enables connections over moderate to long distances. The yagi wi-fi antenna design depicted here is exactly that! It is computer designed, made of wood and wire, and provides high gain and directivity. It is directional - favoring wi-fi signals in one direction and rejecting interference from the sides or behind the antenna. The 15 element wi-fi antenna provides over 15 dB of gain (multiplying your effective radiated power by 31), while the larger 20 element wi-fi antenna provides over 17 dB of gain (multiplying your effective radiated power power by 51). Front to back ratio for both antennas is about 22 dB.
Yagi wi-fi antennas can be rather difficult to make - elements must be precisely cutto the proper length, and spaced at the correct distance from otherelements, or the antenna doesn't work. Before good computer tools were available, a designer used various charts and tables to determine antenna dimensions. These days, however, much of the mind numbing calculation can be carried out in a split second. One excellent tool for crunching design numbers is the yagi antenna modeler, created by Kevin Schmidt (W9CF) and Michael Lee.