Why does an electret microphone require additional power supply?
The reason why an electret microphone (also known as an electret microphone) requires additional power supply is mainly related to its working principle and internal structure.
The reason why the electret microphone requires additional power supply is to provide the necessary bias voltage and current for the field-effect transistor to function properly and amplify sound signals.
This is the key to the proper functioning and sound to current conversion of the polarizer microphone. The following is a detailed explanation of this issue:
1、 Working principle
Electret microphone is a type of condenser microphone with a built-in permanent charge, which works based on changes in capacitance to capture sound signals.
Specifically, there is a very thin plastic film (electret diaphragm) inside the electret microphone head, which is injected with permanent charges during the manufacturing process.
When sound waves cause the diaphragm to vibrate, the distance between the diaphragm and the metal plate changes, resulting in a change in the electric field at both ends of the capacitor, thereby generating an alternating voltage that varies with the sound waves.
This alternating voltage is then amplified and transmitted, completing the process of converting sound to current.
2、 Internal structure
The internal structure of an electret microphone includes components such as an electret diaphragm, metal plates, insulating rings, and field-effect transistors (FETs).
Among them, the polarizing diaphragm is a key component for acoustic electric conversion, while field-effect transistors are used for impedance transformation and signal amplification.
Due to the small capacitance between the polarizer film and the metal plate, the output impedance value is very high (about tens of megaohms or more), so it cannot be directly matched with an audio amplifier.
To solve this problem, a junction field-effect transistor is connected to the inside of the polarizer microphone for impedance transformation.
3、 Power supply demand
Although the electret microphone has a permanent charge built-in and does not require an external voltage source to charge the diaphragm, it still requires voltage to function.
This voltage is mainly used to power field-effect transistors, enabling them to operate normally and amplify alternating voltage signals.
In addition, as an active device, field-effect transistors require a certain bias and current to operate in an amplifying state.
Therefore, the polarizer microphone usually requires a DC bias voltage to ensure its normal operation.
4、 Power supply mode
There are usually two power supply methods for the electret microphone: one is achieved through phantom power provided by recording devices or audio interfaces.
Another way is to directly supply power through an internally integrated battery or external power source. The specific power supply method depends on the design and usage scenario of the microphone head.