The following is the circuit diagram of an LM4780 in parallel output power amplifier circuit. The LM4780 is a popular audio power amplifier IC that can be used in parallel configurations to increase output current and drive low impedance loads more effectively.
In a parallel output setup, two or more LM4780 amplifiers are connected in parallel to share the load. This configuration is especially useful when driving speakers with very low impedance, as it allows for higher current delivery without overloading a single amplifier. However, for the system to work properly, both amplifiers must have identical gain settings.
To ensure consistent gain, resistors Rf1, Ri1 and Rf2, Ri2 must be precisely matched, typically with a tolerance of 0.1%. Any mismatch could lead to uneven current distribution, which might cause one amplifier to work harder than the other and potentially fail.
To further improve current sharing between the two amplifiers, small resistors ROUT1 and ROUT2 are added at the output stage. These resistors help balance the output currents and prevent thermal runaway or damage due to imbalances.
The total load impedance seen by each amplifier in a parallel configuration is calculated as RL (parallel) = RL (total) / number of amplifiers. For example, if two amplifiers are used, the effective load per amplifier is half of the total load. As a result, the maximum power dissipation per amplifier is given by PD (MAX) = VCC² / (2π²RL (parallel)).
(Editor: Circuit Diagram)
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