In this simplest relay circuit, the output socket is not connected to any load, and there is no phenomenon of contact sparking, and there is interference. First introduce the situation: 1 total power supply 5V, powered by an AC-DC power supply module, single-chip power supply 3.3V, powered by an LDO; 2 single-chip IO direct drive triode, IO port set to push-pull mode; 3 total of 2 boards One is the main control board, which has a single-chip microcomputer and an LCD screen. The other is the power board, which has AC-DC modules, relays, and output sockets. The 2 boards have FPC cable connections. Interference description: After 1220v AC power is turned on, the relay is turned on or off instantly, there is a high probability (50%) the system will crash; 2, while the machine is dead, the oscilloscope observes a pulse interference on the 5V power supply. 3 At the same time of the crash, it is obvious that the power indicator on the power module flashed, indicating that the voltage has dropped significantly. Has been tested: 1 in the relay coil power supply part string a 22uH inductor, continue to crash; 2 in the relay coil string a Schottky diode, and then in parallel with 1N4007, then receive 5V power supply there, still crash; 3 more than 2 Come together, crash. Successful test 1 disconnect the relay contact and 220V AC (the end of the figure L), there will be no more pulse interference on the power supply, no more crash; 1 change other AC-DC power supply module, the power supply still exists Pulse interference, but no longer crash, replaced the other four power modules. Suspected to be a relay coil, the board EMC design problem, please explain why the normal phenomenon after replacing other power modules.
The big ant master said: "The best way to solve the EMS problem is not to deliberately eliminate this interference to avoid the system crash, but to find out the way the interference exists and the system does not crash. Otherwise how to pass the EFT? Daily electrical equipment every day In accepting this kind of interference, turn on a light and blow a hair dryer, all of which are a series of pulses. The old T uncle said: "According to the description, there are 2 possibilities for the interference source, and the relay line packs the back potential or the inductive power on the contacts. (Because it is good to pull off 220V.) Suggestion: 1. 4007 string of small resistors, the purpose is to consume back EMF energy, only string 4007, can not consume energy, will cause oscillation
2. The relay is poorly insulated, replaced with new ones or cleaned and dried, and has the condition to change the capacity of the first gear.
Master Chunyang said: "
The high probability is that the insulation between the high-voltage circuit and the low-voltage circuit is poor. The small probability is that the EMC characteristics of the system are too inferior, and it is played by a little electromagnetic induction interference.
You can use the following method to test and verify: use another relay to connect the windings to the drive circuit with short wires, or simply solder the wire package pins of the relay to the PCB. The contacts must be left floating and must not be attached to the PCB. contact. After power-on work, the power line of the power grid is led out by a wire (the wiring on the original terminal and the power grid must be removed), and the relay contacts are respectively contacted. If the contact is instantaneously dead, it indicates that the relay is poorly insulated or the interference is introduced due to distributed capacitive coupling ( I will talk about it later.) If nothing happens, solder the wires of the fuse directly to the relay contact pins (preferably corresponding to the PCB design, but still not connected to the PCB) and try again. No problem, indicating that the problem is on the PCB, which is caused by PCB leakage.
If the ACDC switching power supply used by the landlord has a Y capacitor, then the grounding terminal must be well connected to the earth. Otherwise, the grid will be directly connected to the system through the Y capacitor, causing the system to have a high floating voltage. At the same time, when the system EMC design is not proper, at this time, the transient circuit formed by the relay distributed capacitive coupling can disturb the floating voltage and cause the system to freeze. If this is the case, it will be fine if you pick up the earth, but it still indicates that the EMC design is bad.
Take a good test of these experiments, and think about the theoretical knowledge involved. User yanruiqi friendship reminder: "The most important thing is: Why did the landlord cut L, there is no interference?
I judge: Although the socket does not have a load, there is a magnetic field change when the relay contacts the L contact, or there is a capacitance at the contact surface.
It is recommended to change the relay to see, or only touch the point L, the other contact is not connected, to prevent slight leakage between the two poles of the socket.
Through the statement of the landlord, the power supply problem is more likely, so why is this phenomenon caused by the power supply? From the point of view of the phenomenon, it may be that the power supply transient response power is small (not normal power is small), then when the relay is connected, does it really need such a large instantaneous power?
Usually in the use of this kind of single-chip drive relay, I recommend using a large voltage relay as much as possible with a large voltage, 5v relay coil pull-in steady current value is 89.3mA, and 24v relay pull-in steady current value is 18.7 mA, this is the Ningbo Songle relay data (similar to other brands),
Is it because of the poor transient response of this power supply, the relay coil is energized instantaneously, and the power supply response is poor?
If the landlord is likely to change the DC24V relay to try.
For the circuit of the single-chip drive relay, there are no more than these. The landlord's this is the most common one. I don't recommend this circuit in the project. It may not be a problem when testing. The actual industrial site is not very reliable! There are many people using optocouplers and ULN chips. I also think this kind of trouble. I usually use TLP127 (Darlington type optocoupler) directly. The TLP127 optocoupler is designed for this kind of driving inductive relay load. It is integrated internally. A freewheeling diode, the freewheeling diode outside the relay coil can not be connected, pay attention to the TLP127 IC current maximum 150mA, for the driver to drive DC24V properly, the landlord can test this way, 1, the relay contact is not connected Use a switch directly on the relay to manually turn on and off L to see if it affects
The relay pull-in contact L and another contact are connected. This state change definitely affects your system. There are two possibilities. One is the electromagnetic field to disturb the power supply, and the second is that the relay coil and this L occur. The effect is that the sudden change of the pull-in current of the relay causes the power supply transient to keep up. User hufengweixx said: "
According to your phenomenon, it seems that power supply interference has caused the microcontroller to crash; personally think that the design concept of your circuit itself may be a bit problematic.
1, the relay and the single-chip source need to do more processing, improper handling will be a problem
2, MCU output control relay is best to add optocoupler isolation, relay interference, turn off the instantaneous interference should be very large, without isolation interference directly transmitted to the microcontroller and power supply may be likely to cause a crash;
3. As for the replacement of the power supply, it will not crash. It may be that the new power supply is handled well. Personally, this is not the fundamental solution. It is only the compensation after the emergence of the fundamental problem. It is the key to modify the design of the circuit itself.
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