Four-legged tap, as its name suggests, has a four-foot tact switch, and a four-legged lighter tact switch is always used in daily products, and is relatively occupied. A big part. The four-leg refers to the four pins of the tact switch. Four pins have two groups of switches. When they are pressed, two groups are energized at the same time, and the two groups are opened at the same time. Some people say this. The four pins are for the soldering of the circuit board. In fact, this understanding is not wrong.
Whether it is four foot touch switch or other touch switch, its working principle is more similar, in part due to the number of pins is not the same, the switch is not the same, so it leads to a certain difference in its most fundamental working principle. What is the working principle of the four foot touch switch?
Four foot touch switch works
First, from the normally open contact, normally closed contact combination, in the four foot touch switch, the role of the normally open contact, that is, when the pressure is applied to the normally open contact pressure, this circuit is turned on When the pressure is removed, the original normally closed contact is restored, which is called disconnection. The force of this pressure is to use our hands to open the button and close the button.
Second, when the pressure is removed, the four-legged touch switch will be turned off. The internal structure of the four-legged touch switch is based on the metal shrapnel to protect the force conditions and turn on and off.
The principle of the three- and four-legged touch switch is related to its structure. For example, if 220V AC passes through the bulb H and rectifies the full bridge, it becomes a DC ripple voltage, and is applied as a forward bias to the SCR and R-branch. .
1, during the day, the brightness is greater than a certain degree, the photodiode D shows a bottom resistance state ≤ 1KΩ, so that the transistor V cut-off, the emitter has no current output, one-way thyristor VS because of no trigger current and block. At this time, the current flowing through the bulb H is ≤ 2.2 mA, and the bulb H cannot emit light. The resistor R1 and the zener diode DW bias the transistor V not more than 6.8V to protect the triode.
2. At night, when the brightness is less than a certain level, the photodiode D exhibits a high-resistance state ≥100KΩ, so that the transistor V is forward-conducted, and the emitter has a voltage of about 0.8V, so that the thyristor VS is turned on and the bulb H emits light. RP is a brightness selection element that realizes switching of the switch in the early morning or evening.
4. Regardless of the structure of the touch switch, the four-pin touch switch has four pins in common, and the advantages of the four-legged tact switch over the normal tact switch are very strong. With the welding, everyone can use the four-legged touch switch to adjust and control accurately.