Making a hearing aid using TDA2822

This hearing aid is composed of TDA2822 dual-power amplifier integrated circuit and a small number of peripheral components. Compared with popular machines on the market, it has the characteristics of large output power and wide voltage range. The operating voltage is 1.8-15V, which is suitable for patients with moderate and mild hearing loss.

working principle:

The electrical schematic diagram of the hearing aid is shown in Figure 1. Its working principle is relatively simple: the electret microphone is connected to a high-gain drain output circuit and converts external sound waves into electrical signals. TDA2822 forms a BTL amplifier circuit to amplify the audio signal output by the microphone and drive the earphone to sound with sufficient power. In order to reduce the loss caused by coupling, transformer coupling is used, and C2 is added to the primary to filter out part of the induced noise. The secondary is connected to RP to control the volume. In addition, R1 and C1 form a decoupling circuit to prevent the signal from causing feedback through the power supply; R2 and C6 are frequency compensation for the BTL circuit.

The audio transformer T is replaced by a pocket radio input amplifier. If you wind it yourself, you can use an E14 iron core. The primary and secondary are both wound with Φ=0.06mm enameled wire, 2000 turns each. The volume potentiometer RP uses a WH135 variable resistor directly soldered on the printed board. The headphone jack is a 2.5mm horizontal two-core socket.

As long as the circuit is assembled correctly, it can work normally without debugging. The power supply uses two No. 5 batteries, and the static working current is 6mA