A basic design that steps up a low voltage DC input to a higher voltage DC output is a boost converter circuit that uses the IC 555 integrated circuit.
Here, the circuits central component IC 555 produces a pulse width modulated PWM signal that regulates the other components switching.
Additional parts utilized in this post to complete the circuit are the IRFZ44N, inductor, diodes, resistors and capacitors.
Circuit Working:
Parts List:
| Component Type | Description | Quantity |
|---|---|---|
| Resistors | 1k ohm | 1 |
| Potentiometer 47k ohm | 1 | |
| Capacitors | Ceramic 100nF | 1 |
| Ceramic 1nF | 1 | |
| Electrolytic 100μF 25V | 1 | |
| Semiconductors | IC 555 | 1 |
| MOSFET IRFZ44 | 1 | |
| Diodes | Diode 1N4001 | 2 |
| Diode 1N5822 | 1 | |
| Inductor | Inductor coil 10uH | 1 |
Due to the inductors inability to transform energy immediately, the energy is first stored in its magnetic field before being utilized by the boost converter to increase the output voltage by decreasing the current.
Since both the resistance and the current are constant, the only variable that can vary is the voltage.
The formula for calculating the current across an inductor is Iinductor = V/R.
The circuit is continuously turned on and off by connecting an inductor in series with the voltage source, as seen in the above figure.
To achieve quick switching, we use a MOSFET in conjunction with a MOSFET driver and a switch is connected in parallel to the two components.
A load and a capacitor are connected in parallel to the circuit.
Between the capacitor and the MOSFET there is a diode that is used to halt the current going backwards from the capacitor.
This circuit is very similar to the buck converter and is sometimes referred to as a backward buck converter.
The inductor attempts to resist change in the current to provide a constant input current, and as a result the boost converter acts as a constant current input source, while the load acts as a constant voltage source.
The PWM signal that drives the N channel MOSFET is provided by an IC 555 which provides the MOSFET with its output.
The purpose of the capacitor is to hold the charge and supply a steady output to the load.
The switch is turned on in the first stage of the circuits operation and it is in the off stage in the second.
The light is on Mode of charging
The MOSFET switch is activated in this state. Our chosen MOSFET is an N channel IRFZ44N MOSFET and pin 3 of the IC555 is linked to its gate pin.
A magnetic field surrounds the inductor when the switch is in the ON position because it completes the circuit across it and applies voltage across it.
Everything that is voltage passes through the switch and returns to the source since it provides an extremely low resistance channel.
In order to prevent the capacitor from trying to discharge itself from the MOSFET, which was previously charged during the last on stage, we employ a diode to prohibit the capacitors charge from flowing in the opposite way.
Discharging mode with the switch off
A voltage surge is created while the switch is in the off position because the inductors charging route is not finished.
As a consequence the inductors polarity is reversed and the magnetic field around it collapses charging the capacitor through the diode.
Both the capacitor and the load are charged by the combined energy from the inductor and source.
The switch is the primary part of any SMPS and in this design the N channel MOSFET, IRFZ44N is being used as the switch.
The gate of the IRFZ44N is linked to the 555 IC because it is driven by the weak signal from the IC 555.
The source is linked to ground while the drain controls the circuits negative switching.
Formulas:
Here are some key formulas related to the boost converter:
Boost Converter Output Voltage:
Vout = Vin / (1 – D)
where:
- Vout is the output voltage
- Vin is the input voltage
- D is the duty cycle (0 ≤ D ≤ 1)
Duty Cycle:
D = Ton / T
where:
- Ton is the ‘on’ time of the MOSFET switch
- T is the total cycle time
Inductor Current:
L * di/dt = Vin – Vout
where:
- L is the inductance
- di/dt is the rate of change of inductor current
Capacitor Voltage Ripple:
ΔVout = (Iout * Ton) / (C * f)
where:
- ΔVout is the peak to peak voltage ripple
- Iout is the output current
- C is the capacitance
- f is the switching frequency
These formulas give a general idea of how different boost conversion parameters relate to one another.
For more precise computations, it is crucial to take into account non idealities such component losses and parasitic components.
How To Build:
To build a Simple Boost Converter Circuit using IC 555 following are the below mentioned steps for connections:
- Assemble all the mentioned components from the circuit diagram above
- Connect pin 1 of IC1 555 to ground.
- Connect pin 2 of IC1 555 to pin 6 of IC1 555
- Connect pin 3 of IC1 555 to gate of MOSFET IRFZ44.
- Connect pin 4 and pin 8 of IC1 555 to positive supply.
- Connect pin 5 of IC1 555 to ground through capacitor C1
- Connect pin 6 of IC1 555 to center leg of pot 47k.
- Connect pin 7 to +3.7V input positive supply through resistor R1, connect diode D2 to upper leg of pot 47k, and diode D3 to lower leg of 47k pot through pin 7 of IC1 555.
- Connect capacitor C2 to ground through pin 2/6 of IC1 555.
- Connect gate of MOSFET IRFZ44 to pin 3 of IC1 555, connect drain to positive supply of +7.5V output, connect source of to ground.
- Connect a capacitor C3 from +7.5V output positive supply to ground.
- Connect a inductor coil and a diode D1 to positive supply.
Conclusion:
The boost converter uses a MOSFETs controlled switching and an inductors energy storage capabilities to successfully raise the input voltage.
The capacitor maintains a steady output voltage for the load, while the IC 555 generates the PWM signal required for effective functioning.
A useful option for applications needing a greater DC voltage than the available input source is provided by this simple yet efficient circuit.