Chip loudspeaker protection device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers
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The IC loudspeaker protection device is designed to work with a stereo amplifier powered by a bipolar source and connected to the load without a coupling capacitor. It turns off the loudspeakers when a DC voltage exceeding -1,2 V appears on any of the outputs of the amplifier, and when any of the bipolar power sources, common in this case to the amplifier and the protection device, fails.
The device includes a time relay that delays the connection of the loudspeakers for a time longer than the duration of transients in the amplifier associated with turning on the power.
The device consists of two low-pass filters (R1C1 and R2C2), a diode distributor (V1 - V4), two comparators made on the op-amp A1, A2, and an electronic key on transistors V11-V13 loaded on the relay winding K1. If the amplifier is working, then with the power on, the diodes V6, V7 are closed by the positive output voltages of the op-amp A1, A2, and the capacitor C3 begins to charge through resistors R9, R12 from a stabilized voltage source on the zener diode V8. At the moment when the voltage on the capacitor reaches 1,3 ... 1,4 V, transistor V12, and then V13 open, and relay K1 is activated, connecting the speakers to the outputs of the amplifiers of the left and right channels.
When a voltage of positive polarity exceeding 1,2 V appears at the output of any of the amplifiers, the output voltage of op amp A1 becomes negative, diode V6 opens, capacitor C3 quickly discharges through it and circuit R11V9, and transistors V12, V13 close. As a result, relay K1 releases, and its contacts disconnect the loudspeakers from the amplifiers. Similarly, the process proceeds when the output of any of the voltage amplifiers of negative polarity appears (in this case, the output voltage of the op-amp A2 becomes negative, and the capacitor C3 is discharged through the R11V9V7 circuit), as well as bipolar voltages of any value exceeding the threshold.
The reaction of the device to the disappearance of the supply voltage of positive polarity is due to the fact that this voltage is used to power the transistors V12, V13. When the supply voltage of negative polarity disappears, transistor V11 closes (bias voltage is supplied to its base through resistor R10 from a source of - 5,6 V), breaking the collector circuit of transistor V12. In both cases, relay K1 is activated and disconnects the loudspeakers from the amplifiers.
The device uses the RES-9 relay (passport RS4 524 200).
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