Soft start protection
When a high current absorbing audio device is powered on, the current flowing through it can reach 4-10 times its average current value, which is an impact on the power grid and the device itself. In severe cases, it can damage the device. At this point, the soft start circuit can suppress the influx of current at the moment of equipment switching, allowing it to smoothly achieve normal protection of the equipment and not cause fluctuations in the power grid. This function is usually realized by the Negative temperature characteristic of thermistor (NTC)
DC protection
When the output stage of the power amplifier is damaged or the static bias is offset, it is possible to transmit a DC signal. For speakers, their working mode only generates impedance for AC signals, and for DC signals, they do not generate any impedance (equal to zero impedance). At this point, the current is infinite, so the coil of the speaker is equivalent to a heating wire that will quickly burn out under DC signals. Therefore, accurate and fast DC protection circuits are very important. The DC protection activation value of the power amplifier is usually set at 2V. When it is greater than or equal to this value, the power amplifier will cut off the output to protect the speaker. Of course, there are also power amplifiers that will cut off the output by burning the built-in DC fuse
Short circuit protection
When a short circuit occurs at the output end of the power amplifier due to certain reasons, the current output by the power amplifier will cycle through its own circuit and become infinite. This situation is very dangerous, so it is necessary to have accurate and fast short-circuit protection circuits to protect the power amplifier equipment. Each power amplifier must have a short-circuit protection function, which is vital and cannot be ignored
Usually, when a short circuit occurs in a power amplifier, it first controls the input signal to reduce its amplitude or even zero. If the situation does not improve (the current flowing inside the power amplifier still exceeds the safety value), it will suppress the output current, making the current flowing inside the power amplifier always lower than the safety value of the output stage transistor
Overcurrent protection
When the load of the power amplifier is too low but has not reached the short-circuit state, the short-circuit protection will not operate, but the output current will be very large and exceed the safe use value of the power amplifier. At this time, the overcurrent protection circuit will intervene and work. The usual approach is to control the input voltage and output current to ensure that the power amplifier always operates within a safe range
Overheat protection
A well-designed power amplifier will not experience overheating protection under normal use, and will only operate when the external usage environment is harsh or internal faults occur. The hottest part of the entire power amplifier is the C-pole (collector) of the output stage transistor, so the temperature sensor for overheat protection is generally installed in the closest place to the C-pole of the transistor or the hottest place on the heat sink. The threshold for overheating protection is generally 95 ℃, and there are also 105 ℃. The extreme withstand temperature of the transistor is 105 ℃.
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