PWM (Pulse Width Modulation) is used to adjust the brightness of a light bulb by controlling the MOSFET. In daily life, we often adjust the brightness of a light bulb by simply pressing a button, causing the light to dim or brighten. Today, we will explore the "secret" of adjusting the brightness of a light bulb and how it can be achieved using MOSFETs.

First, let's consider two scenarios with series resistors and potentiometers:

Assume we have a light bulb with a normal operating voltage of 12V. Typically, to make it emit light, we connect the two terminals of the light bulb to a 12V power source. If we need to adjust the brightness, we can add a resistor in series in the circuit to reduce the voltage across the light bulb, thus dimming it. If further adjustment is needed, we can change the resistance value of the series resistor to achieve different brightness levels.

To achieve linearly adjustable brightness, we can replace the resistor with a potentiometer. By rotating the knob on the potentiometer, we can adjust the brightness. However, a disadvantage of using a potentiometer is that it consumes a large amount of power and can easily lead to significant power loss in the power supply. Additionally, if the potentiometer is subjected to excessive power, it can be damaged.

Apart from the methods mentioned above, are there more efficient ways to achieve brightness adjustment? Of course!

We know that MOSFETs are commonly used in switch circuits. A MOSFET acts as a switch; by applying a voltage to the gate, it can automatically switch on and off, with extremely fast switching speeds.

By connecting a MOSFET in series with the light bulb, we can take advantage of its properties. When a high level is applied to the gate of the MOSFET, it conducts between the source and drain, allowing current to flow from the input to the output. Conversely, a low level at the gate will cause it to be cut off.

As the switching frequency increases, the flickering of the light bulb will become faster until it is no longer visible, appearing as a steady state.

It is important to note that as the switching frequency increases, for example, reaching 1000 Hz, the brightness of the light bulb may decrease. This is because with a continuous high and low level (under the same conditions), the average voltage will reach a balanced state. However, if the duration of the high level is extended, the average voltage will increase.

For example, when both levels are maintained at 50%, with the high level at 10V and the low level at 0V, the average voltage is 5V. If the duration of the high level is increased to 60% and the low level to 40%, the average voltage becomes 6V. Similarly, if the duration of the high level is 90%, the average voltage will be 9V, and so on.

This method is generally referred to as the PWM (Pulse Width Modulation) principle.

When the switching frequency reaches a certain level, the brightness of the light bulb depends only on the magnitude of the average voltage. The higher the average voltage, the brighter the light bulb; conversely, the lower the average voltage, the dimmer the light bulb.

This is how we adjust the brightness of a light bulb using MOSFETs in series and applying the PWM principle. Thank you for reading! If you like this content, please follow and support us! Thank you!

(Note: Some information in this article is referenced from the internet.)