Currently, voltage inverters are used almost everywhere and very often replace traditional linear regulators, which for high output currents, gives a significant energy loss. Circuit described here is a simple Step-Down converter (12V to 5V) built based on the popular and inexpensive chip MC34063. The device is designed to work with 12V car installation, and can be used to charge/power GPS or mobile phones equipped with USB slot. In idle state the circuit is completely switched off and in normal operating conditions it can be automatically turn off when there are no power consumption at the output. The converter can be turn on, by a monostable switch, when load is connected to its output .

How It Works?:

At the beginning is worth to present some information about MC34063 which is monolithic controller comprising most important components needed for DC-DC converters. This device contains of: an internal temperature compensated voltage reference, comparator and oscillator with adjustable duty cycle. Moreover the MC34063 contains also a current limit circuit and high current output switch, which is able to work with currents up to 1.5A. In result to built converter only a inductor, a diode and few passive components are needed. Figure 1 shows the complete schematic of the MC34063 voltage converter. The U2 (MC34063) chip, inductor L1 (100uH/1,2A) and diode D1 (1N5819) are the main components of the presented circuit. The diode is very important, it is used to close path for inductor L1 current, generated when the internal U2 switch is disconnected. The C3 (470pF) capacitor sets frequency of the internal U2 oscillator and for capacitance equal to 470pF the frequency will be around 50kHz. R5 (0,33R/1W) resistor is responsible for output current limitation, all current flowing through the inductor L1, flows also via R5. Current limit is set to around 1.1A, so the same current should flow when the converter output is shorted. Capacitor C1 (100uF/25V) filter power supply voltage, while the C4 (470uF/25V) is used to filtering output voltage. Zener diode D3 (BZX85-C5V1) might protect circuit against temporary voltage increase over 5V.

Construction:

Printed circuit board (bottom side) may be downloaded here. Figure in a mirror image is available here. Helpfull for constructing the top side of printed circuit board will be schematic available here.

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Parts List:

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Questions and Comments:

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