Trigger, relay?

A flip flop is an electronic component that can store the state of a circuit. The simplest is the RS flip-flop consisting of two NOR gates, two inputs and two outputs (see picture). The more complicated ones include a D flip-flop with a clock (CLK) segment and a D (Data) terminal, which follows the state of the D terminal when the CLK terminal is high level, and latches the signal instantaneously when the CLK terminal becomes low level. More commonly used is an edge D flip-flop formed by cascading two simple D flip-flops to store the signal on the lower edge of the clock. It is widely used in electronic components such as counters, arithmetic units, and memories.

The working principle and characteristics of a relay A relay is an electronic control device that has a control system (also called an input loop) and a controlled system (also called an output loop). It is usually used in automatic control circuits. It is actually an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays the roles of automatic adjustment, safety protection, and conversion circuit in the circuit. Working principle and characteristics of electromagnetic relays Electromagnetic relays are generally composed of iron core, coil, armature, contact reed, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, thereby producing an electromagnetic effect. Under the action of electromagnetic attraction, the armature will overcome the pulling force of the return spring and attract to the iron core, thus driving the armature's movable contact and static contact (normally open contact) to attract. When the coil is powered off, the electromagnetic attraction also disappears, and the armature will return to its original position under the reaction force of the spring, causing the moving contact to attract the original static contact (normally closed contact). In this way, it is attracted and released to achieve the purpose of conducting and cutting off in the circuit. For the "normally open and normally closed" contacts of the relay, they can be distinguished in this way: The static contact that is in the open state when the relay coil is not energized is called a "normally open contact"” ； A static contact in the connected state is called a "normally closed contact". The working principle and characteristics of the thermal reed relay The thermal reed relay is a new type of thermal switch that uses thermal magnetic materials to detect and control temperature. It consists of a temperature-sensing magnetic ring, a constant magnetic ring, a reed switch, a thermally conductive mounting sheet, a plastic substrate and some other accessories. The thermal reed relay does not use coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch action. Whether the constant magnetic ring can provide magnetic force to the reed switch is determined by the temperature control characteristics of the temperature-sensitive magnetic ring. Working principle and characteristics of solid state relay (SSR) A solid state relay is a four-terminal device with two terminals as input terminals and the other two terminals as output terminals. An isolation device is used in the middle to achieve electrical isolation of input and output. Solid state relays can be divided into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, with photoelectric isolation type being the most common. The main product technical parameters of the relay: the rated operating voltage refers to the voltage required by the coil when the relay operates normally. Depending on the model of the relay, it can be AC ​​voltage or DC voltage. DC resistance refers to the DC resistance of the coil in the relay, which can be measured with a multimeter. Pick-up current refers to the minimum current that the relay can produce a pull-in action. In normal use, the given current must be slightly larger than the pickup current so that the relay can work stably. As for the working voltage applied to the coil, it should generally not exceed 1.5 times the rated working voltage, otherwise a large current will be generated and the coil will be burned. Release current refers to the maximum current that the relay produces a release action. When the current in the relay's pull-in state is reduced to a certain extent, the relay will return to the unenergized release state. The current at this time is much smaller than the pull-in current. Contact switching voltage and current refer to the voltage and current that the relay is allowed to load. It determines the voltage and current that the relay can control. This value cannot be exceeded when used, otherwise the contacts of the relay will be easily damaged. To test the contact resistance of the relay, use the resistance setting of the multimeter to measure the resistance of the normally closed contact and the moving point. The resistance value should be 0 ； The resistance of the normally open contact and the moving point is infinite. From this, you can distinguish which one is a normally closed contact and which one is a normally open contact. To measure the coil resistance, you can use a multimeter with the R×10Ω range to measure the resistance of the relay coil to determine whether there is an open circuit in the coil. Measure the pull-in voltage and pull-in current, find an adjustable regulated power supply and an ammeter, input a set of voltages to the relay, and insert an ammeter in series into the power supply circuit for monitoring. Slowly increase the power supply voltage, and when you hear the relay closing, note down the closing voltage and current. For accuracy, you can try several times and find the average. Measuring the release voltage and release current is also connected to the test as mentioned above. When the relay closes, gradually reduce the supply voltage. When you hear the relay release sound again, record the voltage and current at this time. You can also try several times to obtain the average release voltage and release current. Under normal circumstances, the release voltage of a relay is about 10~50% of the pull-in voltage. If the release voltage is too small (less than 1/10 of the pull-in voltage), it cannot be used normally. This will threaten the stability of the circuit and make the work unreliable. The electrical symbol and contact form of the relay. The relay coil is represented by a rectangular box symbol in the circuit. If the relay has two coils, draw two parallel rectangular boxes. At the same time, mark the relay's text symbol "J" in or next to the rectangular box. There are two ways to represent the contacts of a relay:: One is to draw them directly on one side of the rectangular box. This representation is more intuitive. The other is to draw each contact into its own control circuit according to the needs of circuit connection. Usually, the same text symbols are marked next to the contacts and coils of the same relay, and the contact groups are numbered to show the difference. There are three basic forms of relay contacts: When the moving-type (H-type) coil is not energized, the two contacts are open. When the coil is energized, the two contacts are closed. It is represented by the pinyin prefix "H" of the word "合". The two contacts of the moving-break type (D-type) coil are closed when the coil is not energized, and the two contacts are open when the coil is energized. It is represented by the pinyin prefix "D" of hyphenation. Switching type (Z type) This is the contact group type. This kind of contact group has three contacts in total, that is, a moving contact in the middle and a static contact at the top and bottom. When the coil is not energized, the movable contact and one of the static contacts are disconnected and the other is closed. After the coil is energized, the movable contact moves so that the originally disconnected contact becomes closed and the originally closed contact becomes open, achieving the purpose of conversion. Such contact groups are called changeover contacts. It is represented by the pinyin prefix "z" of the word "turn". When choosing a relay, you must first understand the necessary conditions.: ①The power supply voltage of the control circuit, the maximum current that can be provided ； ②Voltage and current in the controlled circuit ； ③How many groups and forms of contacts are needed for the controlled circuit? When selecting a relay, the power supply voltage of the general control circuit can be used as a basis for selection. The control circuit should be able to provide sufficient operating current to the relay, otherwise the relay will be unstable. After consulting the relevant information to determine the usage conditions, you can search the relevant information to find out the model and specification number of the required relay. If you already have a relay on hand, you can check whether it can be used based on the data. Finally consider whether the size is appropriate. 3. Pay attention to the volume of the appliance. If used for general electrical appliances, in addition to considering the chassis volume, the small relay mainly considers the circuit board installation layout. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be used

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