Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

450V linear regulator suffers overvoltage spike when switched on at mains peak

Status
Not open for further replies.

Flyback

Well-Known Member
Hello,
We are using a 450V rated LR8 linear regulator in our offline product. If the product happens to get switched on at mains peak then the LR8 gets a voltage of 600V peak at its input (as in the scope shot attached).

However, if we put a 100nF X2 capacitor across live/neutral, then the peak voltage applied to the LR8 is 500V. …However, the peak duration is longer even though its less voltage (as shown in attached scope shot).

Which is less harmful to the LR8?

LR8 Linear regulator datasheet:
https://www.microchip.com/wwwproducts/en/LR8
 

Attachments

  • 500v peak.jpg
    500v peak.jpg
    51.3 KB · Views: 94
  • 650v peak.jpg
    650v peak.jpg
    57.2 KB · Views: 97
The higher voltage is likely more damaging, buth either could zap the device.

Why don't you add a transient suppression diode (TVS) to protect the device?

Or use a zero-crossing start-up circuit?
 
Crazy. I only learned there were linear regulators that could work at 250V a few weeks ago, and now here is one that works at 450V.

Is this the kind of thing you can solve by putting an RC snubber at the input (well, I guess you putting a cap across it it very similar)? It looks like it, but I've never heard of an RC snubber being used for something like startup ringing. What would cause that behaviour?
 
How much current are you drawing from the regulators output?

If it's small, you might consider adding a resistor in series with that 100nF X2 cap to slow it's rise time. And probably get rid of the spike entirely.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top