AC protection device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers
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Using a comparator based on an op-amp, you can create a relatively simple and reliable device for protecting speakers from a constant component in the output signal of the UMZCH and a loss of supply voltage in one of its arms. It will also provide a delay in connecting the load after power is turned on.
The protection device is powered from a bipolar UMZCH source through the simplest parametric stabilizers VD12R7 and VD11R9. The inputs of the op-amp are connected to the diagonals of the diode bridge VD1-VD6. Circuits R3VD1 and R6VD2 create a bias voltage at the op-amp inputs: -0,6 V on the inverting one and +0,6 on the non-inverting one. which ensures a stable log 1 level at the output of the comparator and the open state of the VT1VT2 switch, which includes relays K1 and K2. In this position of the indicated elements, the speaker heads of the speakers are connected to the output of the UMZCH through the closed contacts K1.1 and K2.1 of the relay.
When a constant component greater than two volts appears at one of the outputs of the UMZCH, the polarity of the voltage between the inputs of the op-amp changes and a log level is set at its output. 0. As a result, the switch is on transistors VT1. VT2 closes, the relays are de-energized and their contacts K1.1 and K2.1 disconnect the speaker heads from the UMZCH outputs.
To delay the connection of the load after turning on the power of the UMZCH, the VD7C5 circuit is used. When the power is turned off, capacitor C5 quickly discharges through the diode VD8, preparing the device for the next turn on.
When the negative supply voltage disappears, a voltage of +1 V is supplied to the inverting input of op-amp DA4 through resistor R4, which leads to the disconnection of the load from the output of the UMZCH.
A similar process accompanies the loss of positive power, but with the only difference that in this case, a negative voltage of -5 V is supplied to the non-inverting input of the op-amp through resistor R4, as a result of which the supply voltage is removed from the windings of relay K1. K2.
The author did not develop a printed circuit board, but used a surface-mounted installation. Each ZD 15V zener diode can be replaced with a KS515A or two D814A connected in series, the 1N4001 diodes with a KD105, and the S2316 transistor with a KT602BM. Op-amp - any, but with a fairly low input current (for example, K140UD7). The relays are used with windings designed for a voltage of 12 V and a current of 25...30 mA. and contacts that can withstand a current of 10 A at a switching voltage of 120 V.
A correctly assembled device, as a rule, does not need configuration. If you need to increase the time delay when turning on the power, you will have to replace capacitor C5 with another one with a larger capacity. For other UMZCH supply voltages, the values of resistors R7 and R9 should be changed.
Author: M. Sapozhnikov, Ganei Aviv, Israel
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