Passive electromagnetic buzzer

buzzer is divided into piezoresistive buzzer and inductive buzzer from the structure. The piezoresistive type is a piezoelectric ceramic sheet with very small current. The inductive buzzer is an electromagnetic coil plug-in vibration with very small volume.

is divided into an active electromagnetic buzzer and a passive electromagnetic buzzer according to the driving form. The internal structure of the active buzzer is equipped with an oscillation source. As shown in the following figure, if the BUZZ pin is taken with a low electric frequency, the electromagnetic buzzer will sound directly. However, the internal structure of the passive buzzer has no oscillation source. To make it sound, it must be pushed by a pulse frequency data signal between 500Hz and 4.5KHz. Active buzzers are often more expensive than passive electromagnetic buzzers. Because there are many resonant circuits inside, it is simple to push the pronunciation and can be pushed by pulse signals, while passive buzzers are cheap. In addition, the acoustic wave frequency of passive buzzers can be controlled, and there is a definite relationship between minor scale and working frequency.

optocoupler circuit

let's take a look at the power supply circuit in the figure. the buzzer current is still relatively large, so it needs to be driven by triode, and a 100 ohm resistor is added as the power resistor. In addition to this, a D4 diode is added, which is called a freewheeling diode. Their buzzer is a rational component. When the triode is turned on and off to the buzzer power supply system, there will be on-off current flow through the electromagnetic buzzer. However, I understand that one of the characteristics of inductors is that the current flow cannot be genetically mutated, and the current increases slowly when it is turned on and off. This is no problem. However, when it is turned off, the control loop "switching power supply-triode-electromagnetic buzzer-ground" is disconnected, and all current flow cannot be passed. Where does the stored current flow go, it is consumed by this D4 and the ring road of the electromagnetic buzzer itself, and the reverse impact caused by the inductor current when it is closed is inevitable. Continuation of the amount of current after the shutdown, which is the origin of the name of the freewheeling diode.

Ordinary electromagnetic buzzers on the market are basically unable to meet the demand for waterproofing. As a pronunciation component, ordinary buzzers need to have pronunciation holes to better transmit sound pressure (sound intensity). The existence of pronunciation holes will cause water seepage in the inner wall of the buzzer. If too much water is stored, the normal startup of the buzzer will be endangered. Some electronic devices using electromagnetic buzzers are mostly used outdoors. The changeable outdoor natural environment is likely to suffer from rain and snow suddenly. In other words, water splashing will cause water seepage from the pickup to harm the waterproof of the electromagnetic buzzer. Therefore, the electromagnetic buzzer needs to select the raw material of the buzzer waterproof membrane to achieve the reliability design of the buzzer waterproof structure, thus making the electromagnetic buzzer have very good performance indicators.