Up Down Fading LED Circuit

This circuit drives a motor clockwise / anticlockwise via a pot and reduces the speed to zero when the pot is in mid-position. The current is limited to 200mA and the voltage across the motor is less than 6v, but the circuit shows the principle of Pulse Width Modulation (providing powerful bursts of current to the motor to create a high or low RPM under load) and both forward/reverse RPM via the H-bridge arrangement.

Circuit diagram:

 Up/Down Fading LED Circuit diagram

 

Source : 50-555Circuits

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Compact Switching Step Down Converter By MAX639

Switch-mode power supplies are used in electronic circuits to increase (step up) or reduce (step down) voltage levels in the most efficient manner possible. Compared to linear voltage regulators, switch-mode supplies convert relatively little energy into heat. Their efficiency is thus high. This is a major advantage with compact power supplies in particular, since it sometimes makes forced-air cooling unnecessary. Building a switch-mode supply is considerably easier if you use components that have been specially developed for this application. One example of such an integrated step-down converter is the Maxim MAX639.

This is designed for a fixed output voltage of +5V, with an input voltage ranging between +5.5 and +11.5V. Although this IC is primarily designed for a fixed output voltage, the output voltage can be tailored using a simple feedback network. With the given component values, resistors R3 and R4 determine the output voltage, with R3 = R4 [(Vout / 1.28) – 1] The value of R4 may lie between 10kΩ and 10MΩ, but a value of 100 kΩ is a good choice for most applications. The maximum output current is 100mA. If desired, a different type of Schottky diode with similar specifications can be used in place of D1 (a 1N5817). Inductor L1 must be suitable for a maximum current of 500mA.

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