Designing of 12V to 24V DC Converter Circuit using LM324

The main aim of this project is to design and construct a 12V to 24V DC Converter. Basically, this circuit is a Boost Converter type DC-DC voltage converter. One of the applications of this circuit is the solar electric system. This solar electric system consisting of a 12V solar panel, 12 V input voltage is from the battery storage equipment and the 24 V output voltage will be the input of the inverter in the solar electric system. The circuit is a DC-DC voltage converter built with LM324 IC which is configured as an oscillator to produce the switching frequency and a transistor as the semiconductor switching element.

12V to 24V DC Converter using LM324

Before going to circuit construction and operation we will discuss basics of the Boost type DC-DC converter and LM324 IC. The LM324 is a quad op-amp, which means it has four operational amplifiers inside it; the 12V to 24V DC Converter circuit designed using only two op-amps of LM324.

Boost Converter (Step-Up) Basics

The boost converter is used to step-up/ increase an input voltage to some extent higher level, required by the load. The higher level is achieved by storing energy in an inductor and releasing it to the load at a higher voltage. The major circuit for a step up converter or boost converter comprises an inductor, diode, capacitor, switch and error amplifier with switch control circuitry. The basic circuit of step-up converter is shown below.

12V to 24V DC Converter

Boost Converter Operation

When the switch is ON, the inductor output is connected to ground and the voltage Vin is placed across it. The inductor current increases at a rate equal to Vin/L.

When the switch is OFF, the voltage across the inductor changes and is equal to Vout-Vin. The current that was flowing in the inductor decays at a rate equal to (Vout-Vin)/L.

By the law of conservation of energy, the input power has to be equal to output power (assuming no losses in the circuit). Input power (Pin) = output power (Pout).

Since Vin < Vout in a boost converter, it follows then that the output current is less than the input current.

Therefore in boost converter Vin < Vout and Iin >Iout

LM324 Operational Amplifier

LM324 consists of four independent, high-gain operational amplifiers on a single monolithic substrate. To maintain unity gain each of the amplifier provided with an on-chip capacitor which provides frequency compensation.

Pinout

LM324 IC
LM324 IC

Features

  • Operation of Single or Dual Supplies
  • Unity-Gain Bandwidth- 1MHz
  • DC Voltage Gain- 100dB
  • Input Bias Current- 45nA
  • Input Offset Voltage- 2mV
  • Input Offset Current- 5nA

Applications

  • Summing Amplifiers
  • Multi-vibrators
  • Oscillators
  • Transducer Amplifiers
  • DC Gain Blocks

12V to 24V DC Converter Circuit using LM324 and Working

The circuit diagram for 12V to 24V DC Converter is shown below. IC1 LM324 is the core of this circuit. IC1-A, resistors R1, R2, R3, and capacitor C1 forms an oscillator which operates at around 500Hz. R2 and C1 are used to tune the oscillator frequency. IC1-B is connected as a comparator which compares the output voltage with a reference and feeds back a voltage to the oscillator stage for the purpose of controlling the output voltage.

12V to 24V DC-DC Converter - 12V to 24V DC Converter
12V to 24V DC-DC Converter

A Potential divider using preset R5 is connected to the non-inverting pin of IC1. The output voltage is connected to the inverting input pin through a 100K resistor. An output of this comparator stage is fed to the non-inverting input pin of IC1a through another 100K resistor. The output of the oscillator stage is connected to the base of transistor Q1 and resistor R7 is used for limiting the base current of Q1.

When the output of the oscillator is high, transistor Q1 will be turned ON and the inductor L1 get charged (current through the inductor L1 starts to increase). When the output oscillator goes low, transistor Q1 will be switched OFF and now the only path for the inductor current is through diode D2, capacitor C3, and the load if any.

The flyback diode D2 will be forward biased and the energy stored in the inductor during the ON state will be dumped into the capacitor. Diode D1 acts as a freewheeling diode.

An inductor will always try to oppose any variation in the current passing through it and this property of the inductor is utilized here. When charged it stores energy and when discharged it behaves like an energy source.

The voltage it outputs during the discharge phase is proportional to the rate of change of current through it. As the switching frequency increases the induced EMF (Electro Motive Force) from the inductor also increases.

I hope you have clearly understood the topic of 12V to 24V DC Converter. If you have any queries on this topic or on the electrical and electronic projects leave the comments below.

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