The following is about the correct use of electromagnetic passive buzzer for users to refer to when designing.
The principle of electromagnetic passive buzzer is a kind of electroacoustic device that converts electric energy into vibrating plate by electromagnetic effect. When the internal coil of the buzzer has a certain frequency of electrical signal, it produces alternating magnetic field, and after the magnetic field is strengthened by the iron core bracket in the middle of the coil, the vibrating plate on the magnetic circle is vibrated. The internal structure anatomic map is shown in Figure 1; in detail, please refer to the electroacoustic knowledge > > > the principle of electromagnetic passive buzzer
General electromagnetic passive buzzer working parameters are: coil resistance, rated voltage, SPL value, consumption current, voltage working range and so on.
It is very important for users to match parameters when they are using. Here is an example of how to match the parameters:
For example, you choose to use the FHD-BM1290-0520-42's buzzer; first, we know that the rated voltage of this buzzer is 5Vo-p, the input frequency is 2000Hz, the coil DC resistance is 42 Europe, the SPL value used under the rated condition is at least 85dB test distance 10cm, the consumption current is not more than 70mA, and the voltage working range is 3-7V;
When using this buzzer, the design circuit must meet the following conditions:
1, the signal frequency of the input buzzer is the best 2000Hz, and the frequency of PCB baseplate output with CPU clock signal is more accurate; but if your PCB baseplate output signal has a large frequency error, please pay attention to a principle, first, the frequency error range of the output signal is controlled within 100Hz as much as possible; second, Frequency error design value deviation, that is, can not have the frequency of less than 2000Hz, the design frequency can be more than 2000Hz to 2100Hz, so basically do not affect the normal use, because in the frequency of 2000Hz below the buzzer, some buzzer will become very small (this is the normal error of the buzzer starting point caused by the sound. " It is inevitable), but when the frequency of 2000Hz is above the frequency input, the buzzer will not be more than 2000Hz, and the frequency signal over the buzzer can get the buzzer to get up, so the SPL value of some products will fall little (generally within 5dB) when the frequency exceeds the 2000Hz frequency. If you can't meet the above requirements, you must use a customized buzzer;
2. The signal voltage of the input buzzer must be correct. This voltage is the voltage of the buzzer driving the amplifier part in Figure 2, not the total voltage of the PCB circuit.
3, the power amplifier part that drives the buzzer work is shown in Figure 2, the transistor 2SC3199 must be saturated and guided, that is, the input signal of the power amplifier must be sufficient to drive the transistor to be saturated, and the value of the resistance R1 in the circuit is usually adjusted to meet the value of.
4, the value of the resistance R2 in Figure 2 has no special requirement for 0 European substitution. Some users must use the current limiting resistance for the whole machine limited current protection. The value of R2 is also better to use the resistance under 42 Europe. After using the current limiting resistor, the SPL value of the buzzer will be reduced slightly, and the value of the sound is usually not more than 5dB;
5, the range of the working voltage is 3-7V, the SPL value below 5V will be reduced properly, the SPL value above 5V will be increased properly, and the user can test the actual SPL value in actual use, and the 3V can also be used, but the SPL will be reduced more.