Why is (d) not recommended in OMRON relay driver circuits?

cxq742536574

Why is (d) not recommended in OMRON relay driver circuits? [Copy link]

 

maychang

(d) When the transistor in the circuit is turned off, the current in the relay winding decreases relatively slowly.

However, I have not heard of OMRON making such a suggestion.

tagetage

Can you post all your information? I want to learn from it.

tagetage

I randomly found some information about Omron relays and it is just like what the OP said, it is not recommended to put a diode directly. I put the information here.

J216-CN.pdf (730.46 KB, downloads: 6)

2024-5-21 16:43 上传

点击文件名下载附件

tagetage

maychang posted on 2024-5-21 16:21 (d) When the transistor is turned off, the current in the relay winding decreases slowly. However, I have not heard of OMRON making such a suggestion.

I found some information about OMRON relays and there is actually such a suggestion. Please see the attachment I posted.

maychang

tagetage posted on 2024-5-21 16:45 I found some information about OMRON relays, and there is such a suggestion. You can see the attachment I posted.

[I found some information about OMRON relays, and there is such a suggestion. Please see the attachment I posted]

I see. I have learned a lot.

tagetage

maychang posted on 2024-5-21 16:49 [I found some information about OMRON relays, and there is such a suggestion. Please see the attachment I posted] I saw it. I learned a lot.

I found one that explained it clearly. "Does a relay have to have a diode? How to add it appropriately?"

https://mp.weixin.qq.com/s?__biz=MjM5MTIwMjY1Mg==&mid=2649951876&idx=6&sn=6d88c1b956a23f1d8466223d8c84e9d8&chksm=bebe82b789c90ba1dfae16804fff6d925f0dd 18c29f55ecad645561b81539f3c9cf9a0ec2ac1&scene=27

maychang

tagetage posted on 2024-5-21 16:56 I found someone who explained it clearly. "Does the relay have to have a diode? How to add it appropriately?" https://mp.weixin.qq ...

The article previously stated that [it may cause the adhesion to fail and the contact to become "welded"], which makes sense.

But the last paragraph by the Littelfuse technical expert: "If a diode is added, the back electromotive force will immediately form a short circuit state, and the current will be very large, which will easily burn the coil." This expert does not even know about circuit commutation.

tagetage

maychang posted on 2024-5-21 17:09 The article said earlier that [it may cause the adhesion to fail and the contact "welding" phenomenon to occur], which makes sense. But the last paragraph of Li ...

Check this article for any hints. If the reverse electromotive force has not disappeared, and the relay is powered on again, it may cause a problem. That is, the relay is powered on again in a very short time after the power is cut off.

https://m.elecfans.com/article/1359164.html

maychang

tagetage posted on 2024-5-21 17:25 Check out this article for any hints. Is it "the reverse electromotive force has not disappeared, if the relay is powered on again", then...

This article is not just nonsense in parts, it is nonsense throughout.

[The relay will be powered on again in a very short time after power failure], which will not cause the relay winding to overcurrent and burn out.

The freewheeling diode is 1N4148. It should be considered that 1N4148 is only allowed to pass a maximum current of 100mA. If it is a larger relay, 1N4148 cannot withstand such a large current.

maychang

tagetage posted on 2024-5-21 17:25 Check out this article for any hints. Is it "the reverse electromotive force has not disappeared, if the relay is powered on again", then...

Of course, for OMRON relays, since their operating current is very small, it is appropriate to use 1N4148 as a freewheeling diode.

maychang

tagetage posted on 2024-5-21 17:25 Check out this article for any hints. Is it "the reverse electromotive force has not disappeared, if the relay is powered on again", then...

Saying "the reverse electromotive force has not disappeared, if the relay is powered again, it will work" is enough to show that this person has not figured out how the reverse electromotive force is generated. The induced electromotive force is generated by the change of current in the inductor . The change of current and the current are two different things.

beyond_笑谈

The direction of the inductor current cannot change suddenly, so a diode is connected at both ends of the coil to continue the current.

In the article: Using only a diode may affect the switching performance. It is just a possibility. Should the reverse recovery time of the diode be taken into account here? However, no matter how fast the switching speed of a mechanical relay is, it cannot be faster than the reverse recovery time of a diode. So, it is probably written by a engineer who just joined Omron.

bobde163

The official only gave suggestions. If the scope of application of this suggestion can be explained in detail, or under what circumstances it will affect the circuit function, it will be convincing. My personal analysis is that this circuit that is not recommended may have switch reliability problems in some high-speed switching situations, but it should not be a big problem in most application scenarios.