A big advantage of a switching regulator is that it can step up a lower voltage to a higher one. This type of regulator is also known as a boost or step-up converter.
A boost converter is used to increase the input voltage to a higher level as required by a load. This capability is typically achieved by storing energy in an inductor and releasing it to the load at a higher voltage.
goal
This project aims to boost a 3.3V lithium-ion (Li-on) battery up to 5 volts, the standard voltage used by many devices.
To boost a Li-on from 3.3V to 5V, we will employ a BL8530 integrated circuit (IC), which is a boost converter IC. The converter's input voltage can be between 0.8V and Vout, providing 2.5 to 6V at the output.
This design can include multiple blocks, with the Switch Mode IC integrated and others added externally.
Below is the internal block diagram of IC BL8530. It consists of a MOSFET, used as a switch, and an oscillator to generate the PWM signal. An error amplifier maintains the regulated voltage at the output.
Working principle
The boost converter works on the principle of a switching mechanism, which reduces a large part of the power during the acceleration process.
The converter requires an inductor, diode, transistor, capacitor and oscillator to increase the input voltage.
During the ON period of PWM, the inductor stores energy through the transistor and the capacitor provides the output. During the OFF period, the inductor loses energy through the diode and provides the output voltage.
Components
You will need the components below to design the power supply.
Schematic
External components
The BL8530 IC requires an inductor, diode and capacitor to increase the input voltage. Here are some basic parameters for selecting components…
1. The input and output capacitor. If the power supply is positioned close to the IC, there is no need for an input capacitor. However, an input capacitor greater than 10uF provides stability and removes any voltage spikes on the input line.
An output capacitor of around 100uF is recommended for this project. Anything above this will slow the response and will only be useful when there is a higher current output.
2. The inductor. The equation below can be used to calculate the inductor.
Note: The actual value of the inductor is greater than this as we need to take into account the ESR of the inductor, the capacitor and the diode drop voltage.
If the inductor is smaller than Lmin, it will affect the efficiency and stability of the circuit.
Size considerations
An inductor with a small value may provide a large output current, but it will also be less efficient. An inductor with a higher value can be used to improve efficiency.
Therefore, a small inductor can give the best results if the circuit provides a large output current with a low input voltage.
According to the BL8530 data sheet, a 47uH inductor is ideal in all applications.
3. The diode. The diode will affect the efficiency of the entire system. A general rectifier diode can work well at low load. A Schottky diode is recommended for high loads, such as the 1N5819 or 1N5822, etc.
The suggested values for this project are:
- Inductor – 10uH – 100uH
- Output Capacitor – 47uF- 220uF
- Input capacitor > 10uF
- Diode – Schottky
Designing the circuit
The above equation gives the minimum value of the inductor, but not its actual value. If we use this minimum value in the design, the circuit will be unstable.
For our project, we based our calculations on the 2uH inductor. But during testing, we noticed that a 4.7uH inductor was unable to provide the desired results, leaving the circuit unstable. We decided to use the 47uH inductor according to the IC's technical data sheet. This works well in our design.
Practical observation:
Vout (no load) = 5.07V
Efficiency
Efficiency defines the power loss in the circuit. Lower efficiency led to greater energy loss and vice versa. Energy loss indirectly affects the cost of the system. It is worth calculating the efficiency of the system if you use a battery as a power source or if the circuit is used for a long period. It can be used to estimate the cost of the system.
Using the equation below, it is possible to calculate the efficiency…
E% = (Vout*Iout)*100/(Vin*Iin)
Characteristic curve
Thermal management
Every electronic system dissipates energy in the form of heat, so it is advisable to include a heat sink in the power circuit.
Performance
1. Circuit provides excellent voltage regulation for loads below 200mA
2. 70-80% efficiency is expected given the above results
Advantages of the project
- Requires just a few components
- It is economical and small in size
- Can be used with digital circuits
- Li-ion or Duracell batteries can provide the power source
- Can be used in electronic toys or LED applications
Precautions
1. Use the recommended inductor and capacitor for good efficiency.
2. The circuit capacitor must have a higher rated voltage than the input supply voltage. Otherwise, the capacitor will leak current due to excess voltage on its plates and will burst.
3. Make sure all capacitors are discharged before working on the DC power supply.
4. The rated current of the inductor must be 1.15 times greater than the output current.
