Application circuit of LM1875-dual power supply

LM1875 is a single-chip 30W integrated power amplifier circuit. Its main features: maximum output power 30W
(8n), open-loop gain 90dB, total harmonic distortion 0,02%, power bandwidth 70kHz, maximum current capacity 3A, supply
voltage range 20~ 60VO
    (1) Stability . The circuit works most stably when the closed-loop gain is used at 10dB or slightly greater than 10dB. Like other high-
current amplifier devices, self-excitation will occur when coupling between the output and input occurs due to improper wiring.
A decoupling capacitor of O.lruF can be added between pin 3 , pin 5 and ground.
    The output of the circuit can be connected directly to the speaker or coupled to the speaker through a capacitor. And add a balance network between the output and ground
, use ls/resistor and 0.22vF capacitor in series o
    (2) Distortion. When the output power is 20W on 8n load, when =20kHz, set ∞<o. 05%; when ,2lkHt
, THD<0.02%o
    current limit and ∞)A protection. In normal applications, the operating current is limited to about 4A. When high voltage is applied to the output tube
, the maximum current is reduced to ensure safety.
    When LM1875 drives non-linear reactive loads, such as speakers equipped with protective relays, Due to the effect of the inductor
's reaction potential, the voltage swing on the load may exceed the power supply voltage, causing damage to the transistor. Generally,
reverse voltage bleed diodes are commonly used in circuits to ensure safety. This is the so-called SOA protection. LM1875 is equipped with SOA protection circuit
to ensure circuit safety.
    (3) Overheating protection. LM1875 is equipped with an advanced overheating protection circuit. When the die temperature reaches 170℃,
the circuit automatically stops working. When the temperature drops to 145°C, it starts working again. After that, if the temperature rises again,
it will stop working as soon as it reaches 150℃. In this way, the reliability of overheating protection can be ensured even under continuous faults.