Inductors are most widely used in power supply, boost circuits, and buck circuits, all of which require an inductor to store and release energy. Many beginners are not entirely clear on the principle of inductor-based boost circuits. All boost and buck circuits utilize the important principle that "inductor current cannot change abruptly." That is, the current in an inductor has inertia, and this inertia is the energy stored in the inductor.
In the example LCD screen's series backlight boost circuit, the boost IC mainly controls the inductor's switch via the LX pin. In the electrotherapy device's boost circuit, the inductor's switch is controlled via the microcontroller's PWM port. The explanation might be difficult to understand from text alone, so we'll use a diagram to illustrate the current flow. (Here, we emphasize the "unidirectional conduction" characteristic of diodes; current can only flow in one direction, and cannot flow in the opposite direction.)
First, when the switch is turned on, the inductor is short-circuited to ground, generating current inside the inductor. (The chip contains an internal switch; the transistor in the other diagram also functions as a switch.) Then, when the switch is turned off, the current to ground is cut off, but the current in the inductor cannot disappear immediately and needs a discharge path, so it flows to the load. The load cannot consume that much current, so the inductor current becomes the voltage across the load, boosting the voltage.
In the next cycle, the switch opens, and the inductor generates current. Although the voltage on the right side of the diode is higher than on the left, the current cannot flow in reverse, thus maintaining the high voltage. Then the switch closes again, and the inductor releases energy to the load, causing the voltage to rise further. This cycle repeats, with the inductor continuously charging and discharging, providing pulse energy to the diode. By controlling the ratio of the switch's on and off times, the amount of energy output from the inductor can be controlled. This is how the duty cycle of the control signal is changed to adapt to load variations, ensuring the voltage remains at the required value.
For a typical boost circuit (left side of the image above), there is a load, overvoltage protection (OVP), and voltage detection, and the voltage will rise to a stable value. For a simple boost circuit like the one in an electrotherapy device (right side of the image above), the human body's resistance is in the megaohm range, essentially equivalent to an open circuit. Each charging and discharging of the inductor will increase the voltage downstream of the diode. If measured with an oscilloscope, this voltage will show a stepped increase. By controlling the number of switching cycles, the voltage rise can be controlled, potentially exceeding 200V. Because the amount of electricity is very small, the human body will only experience a slight electric shock, posing no danger.
Boost circuit input-output relationship
A boost converter is a commonly used circuit that can increase voltage from a lower level to a higher level to meet various application requirements. There is a crucial relationship between the input and output of a boost converter, which is essential in its design and use. In this article, we will discuss the input-output relationship of a boost converter in detail, including its operating principle, key components, and how to select appropriate circuit parameters.
I. Working principle of boost circuit
The working principle of a boost circuit is very simple: it increases the voltage through a charging and discharging process. The most important components in a boost circuit are the inductor and capacitor. When the capacitor is charging, the current in the inductor gradually increases, and the voltage in the capacitor also gradually increases. When the capacitor is fully charged, the current in the inductor begins to flow back into the capacitor, causing the voltage in the capacitor to rise even higher. In this way, the boost circuit can increase the voltage from a lower level to a higher level.
II. Key Components of the Boost Circuit
Key components of a boost circuit include inductors, capacitors, and switches. The inductor's function is to store energy; when the capacitor charges, energy is stored in the inductor. When the capacitor discharges, the energy in the inductor is released, causing the voltage across the capacitor to increase. The capacitor's function is to store electrical charge and electrical energy. The switch controls the circuit's operation; when the switch is on, the capacitor begins to charge, and when the switch is off, the capacitor begins to discharge.
III. Boost Circuit
When designing and using boost circuits, parameter selection is crucial to ensure proper circuit operation. The following are some important parameters that require special attention.
1. Inductor parameters
Inductor parameters include inductance and saturation current. Inductance refers to the inductor's energy storage capacity, while saturation current refers to the inductor's maximum current output. When selecting an inductor, the required output voltage and current must be considered to ensure the circuit functions correctly.
2. Capacitor parameters
The parameters of a capacitor include its capacitance and operating voltage. Capacitance refers to the amount of charge a capacitor can store, while operating voltage refers to the maximum voltage a capacitor can withstand. The selection of a capacitor must take into account the required output voltage and current to ensure the circuit functions properly.
3. Switch parameters
The parameters of a switch include switching frequency and maximum current. Switching frequency refers to the frequency at which the switch can perform switching operations, and maximum current refers to the maximum current the switch can withstand. When selecting a switch, the required output voltage and current must be considered to ensure the circuit functions properly.
Summarize:
A boost converter is a commonly used circuit that can increase voltage from a lower level to a higher level to meet various application requirements. The input and output of a boost converter are closely related and are crucial in its design and use. Key components include inductors, capacitors, and switches, and appropriate parameters must be selected to ensure proper circuit operation. Only with correctly selected circuit parameters can a boost converter operate stably and provide the required voltage and current output.
