The circuit of a 750mW bridge-tied load audio amplifier with DC volume control composed of the LM4865 amplifier IC is shown in the figure below. The LM4865 uses an 8-pin SO package and an 8-pin micro SMD package (the numbers in brackets are the SMD package pin numbers), with a power supply voltage of VDD = 2.7~5.5V and a static operating current of IDD = 4mA (typical value).
The LM4865 contains two amplifiers A1 and A2, where the output of A1 is connected to the input of A2, and the two generate output signals with the same magnitude but a phase difference of 180°, so that they can drive the bridged speakers connected between the two output terminals V01 and V02. Compared with a single-ended amplifier, the output power (P0 = 4VDD2 / 2л2RL) generated by the differential bridge output under the same conditions is 4 times that of a single-ended amplifier, and no coupling capacitor is required.
The headphones are connected between the V01 pin of the LM4865 and the ground through a capacitor C0. As long as the voltage applied to the IC pin HP-Sense exceeds the 4V threshold, amplifier A2 is turned off and the speaker is silent. When the headphone is not plugged into the headphone jack, the voltage on the HP-Sense pin is set by the resistor divider composed of R1 and R2, so that the LM4865 operates in bridge-tied load mode. When the headphone plug is inserted into the jack, A2 is turned off. Therefore, the headphone acts as a switch.
Reference address:Bridged amplifier using LM4865
The LM4865 contains two amplifiers A1 and A2, where the output of A1 is connected to the input of A2, and the two generate output signals with the same magnitude but a phase difference of 180°, so that they can drive the bridged speakers connected between the two output terminals V01 and V02. Compared with a single-ended amplifier, the output power (P0 = 4VDD2 / 2л2RL) generated by the differential bridge output under the same conditions is 4 times that of a single-ended amplifier, and no coupling capacitor is required.
The headphones are connected between the V01 pin of the LM4865 and the ground through a capacitor C0. As long as the voltage applied to the IC pin HP-Sense exceeds the 4V threshold, amplifier A2 is turned off and the speaker is silent. When the headphone is not plugged into the headphone jack, the voltage on the HP-Sense pin is set by the resistor divider composed of R1 and R2, so that the LM4865 operates in bridge-tied load mode. When the headphone plug is inserted into the jack, A2 is turned off. Therefore, the headphone acts as a switch.
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