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Variable Voltage Output from 12V Battery Source

2016-05-11 22:50  
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Figure 1 

The circuit was designed to provide a variety of voltages to some electronic equipment with the use of a 12V battery as the power source.

74HC14 – a hex inverting Schmitt trigger designed as high-speed Si-gateCMOSdevices compatible with low power SchottkyTTL, capable of transforming slowly changing input signals into sharply defined jitter-free output signals while being utilized for monostable & astable multivibrators and wave & pulse shapers7824 – a 1A positive voltage regulator that is a monolithic integrated circuit designed as fixed-voltage regulators for a wide variety of applications including local on-card regulation with internal short circuit current limiting, internal thermal overload protection, output transistor safe-area compensation, no external components required, output current in excess of 1.0A, and availability in standard 3-lead transistor package7805 – a 3-terminal 1A positive voltage regulator with output transistor safe area compensation, internal short circuit current limiter, output voltage of 5V, 12V, and 15V, internal thermal overload protection, no external components, and current output in excess of 0.5A7912 – a 3-terminal negative voltage regulator with several fixed voltages which makes it useful in a wide range of applications like split power supplies and can provide local on-card regulation, eliminating the distribution problems associated with single point regulation, can deliver over 1.5A output current if sufficient heat sinking is provided and obtain adjustable voltages and currents if used with external componentsTIP31 – a standard type ofNPNbipolar junction transistor used for medium power linear switching applications

With the functions of the circuit, it can provide large or small voltages with positive or negative polarities. The concept of the circuit is based on the oscillator that provides an approximately 7 KHz of frequency through the RC combination of R1 and C28 which are connected in parallel. This circuit leads to the remainder of the gates of IC1. This frequency oscillator is essential for the current of the drive the transistors Q1 up to Q4 in line.

There are two cascaded circuits that are made up of diodes and capacitors. These circuits are made up of D1 up to D4 and C14 up to C17 for the negative voltage or -12 V while D5 up to D9 and C19 up to C23 comprise the positive voltage or 24 V. This positive voltage is used to drive the corresponding stabilizers which contain inductors in its outputs. The last remains and leftovers of oscillation are being removed by the action of stabilizers since they are designed to provide standard reference for the electronic device.

The output of the circuit can provide a range of current from 100 mA up to 200 mA. During the operation, the total time that the battery can supply the desired current depends on the capacity based on the ampere-hour measurement. A suitable heatsink should be placed for all the transistors and the stabilizers in order to lessen the heat created by the components.

C1-4-8-12-18=100nF 100V
C2=220uF 25V
C3-9-=680nF 63V
C5-11-26=4.7uF 16V
C6-7-10-27=47uF 25V
C14-15-16-17=220uF 25V
C19-20-21-22-23=220uF 25V
C13-24-25-29=100nF 100V
C28=3.3nF 63V
This 12V variable output power supply is used commonly for powering MP3 players, PDA’s, cellular phones, and other similar equipments. The use of this type of supply that utilize rechargeable batteries provides several benefits which includes reduced impact on environment and convenience to user because of simple recharging of the battery.


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