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Circuits Careers Videos Features Technical Articles Electronics of Things Special Subscription TI Design Aerospace Automation Automotive Communication Consumer LEDs Medical Power Management Solar Test & Measurement Related Circuits CELL-PHONE-CONTROLLED AUDIO/ VIDEO MUTE SWITCH Light-Operated Internal Door Latch 8-Digit Code Lock for Appliance Switching Simple Key-Operated Gate Locking System Mains Box Heat Monitor Subscribe to Electronicsforu.com Login | Register | Advertise | About Us | Contact Us C I R C U I T L A B Versatile DC-DC Converter Raju Baddi Here is a versatile power coupler that connects a device to 5V-19V DC generated from AC mains by a power adaptor. Power adaptors come in different voltage outputs like 5V (for mobile phones), 12V (for external hard drives) and 19V (for laptops). Sometimes the power adaptor may have a voltage rating higher than the required voltage. With the converter circuit given here, the adaptor can be used to power any device at a lower voltage. For instance, by using a 19V laptop adaptor, you can power a TTL circuit at 5V. There can also be other instances when one needs a 3V or 6V supply. All these and many other intermediate voltages are easily possible with this versatile converter circuit when used together with any off-hand power adaptor. Fig. 1 shows the circuit of the DC-DC converter. Smooth reduction in the voltage is achieved using the LM317 regulator IC. The complete unit can fit inside a piece of a glue stick tube. Adjusting variable resistor VR1 gives the desired output voltage. The output voltage is read using a 0-100μA ammeter, whose series resistance R* is chosen such that the maximum desired voltage could be covered. For instance, if full-scale deflection (FSD) current of the meter is 100 μA and you need an output voltage of up to 15V, then R* = 15/0.0001 = 150 kΩ. The desire d value of R* is obtained by using 150-kilo-ohm preset VR2.
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