Here is just a summary of the relay-related ~ Continue to update the first part whaosoft aiot http://143ai.com
The application of the relay, I believe everyone knows that it can work as long as it is powered on and off in the circuit. This article discusses its application details.
popular connection
In the figure, the coil of the relay passes through Q1 as a switch to turn it on and off. D1, as a freewheeling current, consumes energy in the coil.
Features of the relay
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Pull-in current is greater than release current
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The holding current is less than the pull-in current and greater than the release current
The above two points are "common faults" of relays. You can do an experiment or read the manual.
Advantages and disadvantages of popular circuits
As we all know, the coil of a relay is equivalent to an inductor, and its current cannot change suddenly. When it is released, the moment Q1 is cut off, the coil will still maintain the original current. If the diode D1 is not connected, the generated voltage is theoretically infinite (when the external circuit load is infinite), in popular circuits The connection of D1 provides a release channel for the energy in the coil.
However, if (theoretically) the diode is ideal, that is, it only conducts in one direction without any power consumption, then, when the relay is released, the current in the coil will always maintain the maximum current when it is pulled in (and if the coil is ideal ), this condition will prevent the relay from releasing.
The actual diode and coil are not ideal, so it can be released. The pull-in to release of the relay is determined by the current in the coil. If the equivalent resistance (DC) of the diode and the coil is small, then its release time will be very long, otherwise, it will be short.
From this point of view, the advantage of the popular circuit is that it provides an energy release channel when Q1 is off; its disadvantage is that the release time may be further shortened.
other connections
I have seen the circuit in the figure below, and I have seen the connection without diodes in the figure below. These connections have taken into account the reverse voltage when the suppression switch Q1 is off, but have not considered the issue of release time.
Recommended connection
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Add resistor R1 to make energy release faster.
In the above figure, when the coil is turned off by Q1, the energy is mainly consumed by R1, so that the relay can quickly drop to the release current.
The choice of R1 is determined by the highest reverse voltage of Q1 and the working current of the coil. The larger the resistance, the shorter the release time.
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Reduce power consumption while relay is holding
As we all know, a larger current is required when the relay pulls in, and the current does not need to be the same as the pull-in state to maintain the pull-in state.
Connecting R1 and C1 in the figure below will significantly reduce the holding power consumption of the relay. Before the relay pulls in, C1 has been charged to the power supply voltage, and C1 will supply power to the relay at the moment of pull-in to ensure the high current required for pull-in. When closed, the current supplied to the coil comes from R1, which limits the current to a smaller state.
