Keywords: Increase speaker protection circuit for automobile power amplifier
Increase speaker protection circuit for car amplifier
I. Working principle
The speaker protection circuit is shown in Figure 1. Mainly composed of midpoint potential detection circuits, delay circuits, and relays. The circuit work process is:
At the moment of the sound power supply, the voltage cannot be mutated due to the capacitor C3, it can be seen as a short circuit, then the time base circuit 555 2, 6 foot potential is higher than 2 / 3VCC, so 555 is in a reset state, 3 foot output low electricity Flat, transistor VT2 is closed, and the relay JK normally open contact does not operate. At the same time, the + 12V voltage is charged by the resistor R4 to the capacitor C3, and the 255 after delay is about 5s (second). 6 foot potential is reduced to 1 / 3Vcc, 555 trigger, 3 foot is changed from low to high electricity Flat, transistor VT2 is turned on, the relay JK is applied, and the normally closed contact is closed, thereby achieving the latency to access the speaker access amplifier, completely eliminate the shock of the large current to the speaker when the boot is turned over.
When the audio power is turned off, the + 12 voltage disappears quickly, but the power amplifier output signal does not disappear immediately, and the impact noise generated by the shutdown process is also avoided.
When the power is abnormal or accidentally damaged, the medium point is too high (higher than 1.8V), the DC voltage is limited to the R1, R2 flow, sent to C1, C2 filter and D1 ~ D4 rectification, about 1 ~ 2s (second) The transistor VT1 is turned on, 555 4 pin is lowered by high level, 555 is directly reset, 3 foot output low, transistor Vt2 cut, relay JK is out of electricity, normally open contact, the speaker The power amplifier circuit is disconnected, effectively protecting the speaker is not damaged.
Changing the parameters of R4, C3, adjustable speaker protection circuit The length of the boot delay time is generally set to 5 s (second).
Second, component selection
555 Be sure to use a CMOS time base circuit with a low power consumption. VT1, VT2 use 9014, C1815 small power plastic transistor, requiring current amplification of β>100. D1 to D5 are used with 1 N4148 silicon switch diode, D6 is used for power supply to protected, and optionally 1N4001 to 1 N4007 silicon rectifier diode. R1 ~ R5 is used in 0.5 W-color ring metal film resistance. C1, C2 use high quality aluminum electrolytic capacitors, C3 should be used for small tantalum electrolytic capacitors having small leakage, high precision, otherwise affect delay accuracy. JK is selected with a 12 V / 7 A double relay (left, right channels), such as JZC-22F.
Third, production and debugging
Figure 2 is a PCB board diagram of a speaker protection circuit. Its actual size is about 50 × 43 mm.
Specific production is as follows
First, the power amplifier output is cut with the lead wires of the speaker, and the two sets of outputs, C, C, C, C, and D, respectively, respectively, respectively, respectively, respectively, and right sound speakers, respectively, the power supply of the speaker protection circuit, according to the circuit shown in Figure 2. Can be obtained from the gathering machine, can not be obtained from the car 12 V power supply, otherwise it is not to start / shut down protection; if it is the settlement machine configured by the diesel car (using 24 V power supply), it is required to add a buck circuit. (See Figure 3), power supply to the speaker protection circuit to prevent the power supply voltage to damage the IC.
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