The input capacitance of the three-terminal voltage regulator is determined according to the load. If a high-power relay with a small DC resistance is used, the capacitance above 470UF should be used. Because the resistance of this relay is relatively large, the actual measurement is about 1K , That is, the current consumption of this circuit should be below 20MA. The 47UF capacitor can work normally in the experiment. It is feasible to use a 100UF capacitor in the circuit. If this capacitor is too large, it will not be able to shut off the load and the amplifier even when shutting down. Connected, causing impact on the headphones. Since the working current of this circuit is very small, it is possible to replace the three-terminal voltage regulator circuit with 78M15 or 78L15.
Schematic diagram:
The basic functions are:
1. Turn on the headset after the start-up delay. According to the board I made, the headset will be connected for about 3-5 seconds after the start-up to protect the headset from the impact of the start-up current.
2. When the power is turned off, the filter capacitor of the power supply is selected relatively small. After the power is turned off, the connection between the earphone and the amplifier is almost simultaneously disconnected to protect the earphone from the current impact of the shutdown.
3. Abnormal output DC voltage protection. After a simple experiment, when an output voltage of + 1.5V appears at the output of the amplifier, it can be disconnected within 1 second, and when the amplifier has a negative voltage output, the protection operating voltage is relatively high. .
It took 3 hours to finally solder the amp's protection circuit. Because the components are not handy, the parameters are inconsistent with the above schematic. It is gratifying that the welding is successful. Pay attention to the small black between the input and output terminals The rectangular parallelepiped is the miniature relay of Japan. It is the most suitable for protecting earphones. Of course, you can also use a large relay and use it as a horn protection. The PCB board has been made in the form of dual relay installation.
Relays used in the circuit:
Is the finished circuit board made small? The area of ​​the PCB spanner is 10CM * 4CM
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The following is the two-level protection circuit diagram of the RS485 bus. When a lightning strike occurs, the induced overvoltage is introduced from both ends, and GDT is used for first-level protection.
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This paper gives several motor protection schemes. It not only has fast response and reliable control, but also greatly reduces the production cost of the protection device. The protection ...
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Protection can also be used to reduce leakage in cable connections. Figure 12 shows the principle of drive protection to prevent the leakage resistance of the cable from affecting the measurement of small currents. in...
The relay triggers the normal movement of the mechanical metal contactor. After contact, the connecting wire plate is actually smaller than before starting. The machine with the surge protector circuit of the opposite protector ...
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When the power supply output is overloaded or short-circuited, the Vce value of the IGBT becomes larger, and protective measures can be taken for the circuit according to this principle. It is usually used for this ...
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The working principle of the overcurrent detection sensor is shown in Figure 1. The secondary current of the converter obtained by the converter is converted into a voltage by I / V, and the voltage is DC ...
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For over-voltage protection control, the specific circuit is shown in Figure 3: The rectifier diode D4 is connected to the over-voltage protection relay JDQ1 output.
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When the speaker protection circuit is connected to the audio power, the voltage across the capacitor C3 cannot be abruptly changed, which can be regarded as a short circuit.
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The speaker protection circuit is mainly composed of a midpoint potential detection circuit, a delay circuit and a relay.
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The normal AC mains power is 220V. It is provided by a phase line L and a neutral line N. If in the maintenance of the power grid or transformer, the other phase wire is mistakenly connected as a neutral wire ...
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This protector uses a 230V breakdown voltage protector. And use an effective ground.
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A challenge for design engineers is to retain and / or add circuit protection devices that help protect automotive electronic systems from possible overload conditions ...
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Although the hearing protector circuit is designed for the MC34119 amplifier, it should be used with similar integrated circuit equipment or applications.
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This anti-bounce circuit will maintain the electrical noise generated by the mechanical switch (S1) from reaching the next row of circuits.
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In the picture, VH is the drive voltage of 7.2V thermal print head, and the supply of VH is controlled by the normally open relay. Thermal print head overheat protection circuit protects ...
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The time that the IGBT withstands the overcurrent is only a few microseconds and the overcurrent resistance is small, so the first thing to pay attention to when using IGBT is how to carry out the IGBT protection circuit ...
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The IC regulating valve protection circuit protects the integrated circuit voltage regulator under various faults.
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The voltage comparator LM339 is used in the circuit to monitor the power supply voltage. If the voltage at pin 5 is lower than 1.8V, the RAM stops working and B + outputs high power ...
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Water enters the motor, and the probe A is submerged. A is connected to the chassis through the water, the relay K is attracted, the normally closed contact is disconnected, the KM is de-energized and released, the motor ...
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It can act when the leakage current reaches 30mA: when there is no leakage current, the permanent magnet of the leakage tripping device attracts the armature and is in a normal working state.
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