Dumb question regarding SMPS

The input filters are discharged and draw high current for a cycle or two..

Variations in design. Some have a thermistor to limit the rush current.

The input filters are already charged.

It is caused by very poor and cheap design. Be careful where you plug in as fumes and dust ignite with a bang. Devices like this are not allowed in certain areas.

P.S. drawing arcs is not artistic license. lol

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Dumb switching power supplies have a bridge rectifier and a big electrolytic filter capacitor. If you plug them in near the peak of the AC line waveform, the charging current will spark.

Better supplies, with inrush limiters, or PFC (power factor corrected) front-ends, have much less inrush charge.

Ask Jim for details. He is *so good* at designing switching power supplies.

Indeed I am >:-) ...Jim Thompson

That verifies it.

Jamie

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I like the ucc28019a. works like a champ. Undervoltage lockout too ;)

Cheers

Sarcasm. He's screwed up everything he's posted so far.

He did apologize for calling me a fraud, when he'd messed up.

I wonder why he's designing a discrete SMPS for a Chinese company. That's clearly not his skill set.

Not my normal task for them. It's been chips. Their power supply designer went AWOL and I was asked to fix a flaky start-up... just a "patch" in a BIG design :-( Just about there, in spite of what you might think... had to remember stuff I haven't done since about 1985. ...Jim Thompson

So does the L6561. But poorly documented and no model; and ST ignores my pounding on their door >:-)

If I could make major changes I'd design ST out _forever_! ...Jim Thompson

Might be the new normal. I want to design in a National video driver, LMH6722. Has a thermal pad under its belly. In the datasheet they forgot to mention where its s'posed to be connected to. Probably V- but I'd rather make sure. Filed a support ticket with the new owner TI on 10/2. Got a service request number.

Today is 10/8 and (finally! ... or so I thought) there was a message in the inbox this morning. A form letter, merely saying that, tada, a service request number has been issued. New number: Same as the old number.

So I responded politely as to when I might be expecting an answer. No response all day.

Hurumph!

Well, I'm not going to get you out of trouble on your next pass. Twice is enough.

Get one and ohm it out.

No kidding, that may be the only way :-(

Just made a CAD model for a 100-TQFP processor. Now I know why I chose to become an analog guy and not a digital one.

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They're either overworked or lazy, so they punted. Probably the responders are graded based on how fast they turn around responses, and on yours they already hit infinity.

An idiot who can't even do simple connect-the-dots layouts.

Yep, you just reinforced anyone's faith in your abilities. Not.

Lo and behold, just as I wanted to order samples I finally had a "You've got mail" event. TI support said the pad is not connected to anything. It can be left floating (which I'd never do, of course), connected to V-, or connected to GND (which I'll do).

Do you mean a PCB decal, or an actual Autocad sort of thing?

PADS makes IC decals really fast, for sort of standard things with rows of numbered pins.

Are you doing 3D Solidworks sort of physical modeling? It is fun to finally spin that stuff around in space, or take a virtual walk under the IC pins.

The ground plane is a good place to dump heat, plus some additional heat spreader patterns on other layers, when possible. The optimum via pattern to do that isn't obvious. We've had debates around that issue.

I wish I had some software to help with that. We just sort of guess.

Data sheets should state the power pad electrical connection. Often it's missing, or obscure.