+5v Voltage Regulator = 6v output? (BA50DD0T)

Hey gang-

Been meaning to post on this for the last week or two.. (but forgot & have been lazy)

While at work today I remembered about this..and wanted to get some feedback.

I got a couple (what I thought were) fixed +5v/2A linear voltage regulators from Mouser the other week..

Mouser Part#:
755-BA50DD0T

Mfr Part #:
BA50DD0T

Mouser Link:

Datasheet:
https://www.mouser.com/datasheet/2/348/baxxdd0-e-208708.pdf

I got them in the mail... used my PSU so I could check the stable output.....

When I metered the output.. I was get something like +6.25v??

What the????

I tried another one... same deal.

I thought perhaps my crappy meter was off or low battery.. I test the PSU directly at different voltages.. and its spot on!??

What am I missing here? How can an advertised fixed +5v/2A linear regulator NOT output the correct fixed output?
Could I be doing something wrong?

Link to product and datasheet are above.

Thanks for any enlightenment.

Did you add capacitors to the input & output?

From the datasheet:

Please attach a capacitor (greater than 0.33μF) between the Vcc and GND.
The capacitance values will differ depending on the application, so please take this into account when configuring the terminal...

...Please attach an anti-oscillation capacitor between Vo and GND. The capacitance of the capacitor may significantly change
due to factors such as temperature changes, making it impossible to completely stop oscillations. Please use a tantalum
capacitor or aluminum electrolysis capacitor with favorable characteristics and small internal series resistance (ESR) even
at low temperatures.

LDO Regulators are notorious for self oscillation. And, according to the datasheet, this one appears to be more sensitive to output capacitor ESR than most -- probably because of the higher current capability. The datasheet has a couple of graphs that show stable operation regions, for the output capacitor -- it's important to conform to this.

In other words, my guess would be that your Regulator is oscillating.

Also, circuit layout may be an issue. The capacitor needs to be as close to the regulator as possible.

BTW: make sure you're using an electrolysis capacitor! ;D [joking!]

Thanks..

I do have caps on the input and output...

Im at work currently.. and dont recall the values specifically.

What diagram should I be following.

I'm not that great at datasheets always.. and this one seems to be even more awkward for me to read.

Usually there is a simple wiring diagram to follow.. this mas many (and what I though didnt apply to me needs/application)

p.s. what does it mean when a v regulator is 'oscillating'?

xl97:
Thanks..

I do have caps on the input and output...

Im at work currently.. and dont recall the values specifically.

Just throwing caps on this thing, willy-nilly, may not be enough. You selected what looks like a very finicky part.

What diagram should I be following.

If you look for the section that talks about the output capacitor, you will see the diagrams I'm referring to.

I'm not that great at datasheets always.. and this one seems to be even more awkward for me to read.

Well, then...I hate to say it, but you may have bit off more than you can chew, here. Or, it might be time for you to bite the bullet and suffer the drudge of actually learning how to read datasheets. Man, I remember how confusing datasheets were, back when I started in electronics. But, perseverance -- fueled by a burning desire to make it work -- pushed me past the period of confusion, into relative clarity (there are still things that throw me, but again...perseverance!). It's like learning a new language. It's hard at first, but gradually, it starts making sense. BUT, you are starting with a more difficult datasheet. You can either suck-it-up and push through the frustration and possibly get the reward of a giant leap forward, or you can abandon this for now, and find an easier part to play with. Like an LM323K:

https://www.jameco.com/z/LM323K-Major-Brands-Standard-Regulator-5-Volt-3-Amp-3-Pin-2-Tab-TO-3_23667.html

Usually there is a simple wiring diagram to follow..

Yes, but this is no simple part!

this mas many (and what I though didnt apply to me needs/application)

Huh?!? Please proofread your posts!

p.s. what does it mean when a v regulator is 'oscillating'?

More proof you're out of your league with this one.

It has to do with something called "positive feedback" and goes beyond even my understanding, since I'm not really an "analog" guy. My strengths are digital and programming. But, if you know how to read a datasheet, and follow it's recommendations, and if you know a bit about PCB layout considerations, you can usually get by. At least on a "hobbyist" level.

This is probably over your head, but it gives you a taste of what's to come, should you make the effort to really learn this stuff:

http://www.learnabout-electronics.org/Oscillators/osc11.php

BTW: I read that article on oscillators, and I learned something [that Negative Feedback is used to stabilize an oscillator--i.e. keep the amplifier at a gain of 1]! You see...there's always something more to learn! :wink:

And to elaborate on the reason for understanding how an Oscillator works: a Voltage Regulator has an Amplifier in it. And, for reasons I don't fully understand, this amplifier can become an Oscillator -- basically when "Positive Feedback" inadvertently occurs [again, for reasons I don't fully understand -- also, a regulator needs Negative Feedback to function properly], and has to do with the magnitude of the output capacitance and the ESR of that capacitor. And, again for reasons I don't fully understand, LDO regulators are more sensitive to conditions that can produce oscillation. The part you are trying to use is an LDO! And not only that, but the fact that it is made to function at such high currents, apparently, makes it EVEN MORE SUSCEPTIBLE TO OSCILLATION! So, this is very ANTI NOOB!

To clarify…

These were to be read (sorta) together:

“Usually there is a simple wiring diagram to follow…”
&
this HAS many (and what I thought ‘were diagrams that’ didnt apply to me needs/application) ← added clarity between single quotes, and typo fixed)

  • as in many diagrams… with many configurations…

I read this line as well:
“Please attach a capacitor (greater than 0.33μF) between the Vcc and GND”

And the diagram directly under it as well… (using a 22uF cap on the output)

  • which I believe is the same cap value I used when I looked at this datasheet originally… (again not at home to confirm, but this is my current stance/belief)

I guess this a finicky part… (you are right)…
or at least… crummy documentation IMHO at best.

It was chosen as a drop in replacement for a LM7805AC regulator for more current! (same pinout and more current with a fixed +5v output)… actually it was recommended to me to be clear.

and I appreciate your response…

My saying I’m not great at datasheets, is not to be confused that I dont try and do any work on my own.
I have

As far as asking about oscillation… I always thought it just meant ‘ripple’ in your power/rails…etc… but I asked to get a better understanding instead of just assuming ‘ripple’ (not stable)

xl97:
I guess this a finicky part... (you are right)...
or at least.. crummy documentation IMHO at best.

Documentation seems fine, to me.

It was chosen as a drop in replacement for a LM7805AC regulator for more current! (same pinout and more current with a fixed +5v output).... actually it was recommended to me to be clear.

Well, then, that's different.

My saying I'm not great at datasheets, is not to be confused that I dont try and do any work on my own.
I have

I didn't think that - I took it for merely that you need some more "education". I made no judgment in terms of your ability or willingness to acquire that education.

As far as asking about oscillation... I always thought it just meant 'ripple' in your power/rails..etc.. but I asked to get a better understanding instead of just assuming 'ripple' (not stable)

Ripple, besides being cheap wine, can also be a product of oscillation, but oscillation is a term describing an electrical process. And, in fact, you could say that ripple is an oscillating voltage, but it, in itself, is not oscillation. Ripple is merely a description of a type of noise that rides on a DC voltage.

And, my feedback was not meant to be pejorative. I was merely putting forth what seemed to be the state of your present abilities.

xl97:
p.s. what does it mean when a v regulator is 'oscillating'?

It means that the regulator's automatic control system that is ideally meant to allow the output to stay relatively constant (fixed) ------ no longer does the desired (wanted) thing. The behaviour (ie. whether it oscillates or not --- or how close it is to being pushed over the edge into unstable territory) depends on components internal to the regulator and also external to it .... like capacitors or whatever else is connected. To properly understand this sort of thing.....it requires a bit of electronics theory and maybe some automatic control theory ....that will basically explain how oscillators are formed. In this case, it's about conditions that prevent an oscillator from being formed. Some maths would be involved.

When they say that LDO regulators require suitable choice of capacitor ... with some value of capacitance and some value of effective/equiv series resistance....... this just means that the capacitor (and practical values associated with it... like its 'ESR') can be used to set-up or configure the regulator's behaviour so that it doesn't do want we don't want - under the conditions that we want to operate at.

xl97:
These were to be read (sorta) together:

“Usually there is a simple wiring diagram to follow…”
&
this HAS many (and what I thought ‘were diagrams that’ didnt apply to me needs/application) ← added clarity between single quotes, and typo fixed)

  • as in many diagrams… with many configurations…

Whew! That was a tough sentence to parse!! But I think I finally figured out that you’re trying to say. Yes, the datasheet covers a number of different variations, and such datasheets can be a bit daunting. Hard to find the sections that are relevant to your particular version.

I read this line as well:
“Please attach a capacitor (greater than 0.33μF) between the Vcc and GND”

And the diagram directly under it as well… (using a 22uF cap on the output)

  • which I believe is the same cap value I used when I looked at this datasheet originally… (again not at home to confirm, but this is my current stance/belief)

So, it sounds like you need to learn about the concept of ideal vs reality. The ideal capacitor has merely capacitance. The real world capacitor has, along with it’s inherent capacitance, also resistance [“ESR”] and a certain amount of inductance. The inductance component is more prevalent in a capacitor that is manufactured by rolling the “foils” into a cylinder. For instance an Electrolytic Capacitor. But that’s an aside.

All capacitors have ESR, and this is a parameter that is just as important as capacitance, in this particular instance. In other words, not just any 0.33μF cap is suitable for this application. It needs to have the correct capacitance AND an ESR that’s within the range of Stable Operation.

It was chosen as a drop in replacement for a LM7805AC regulator for more current!

I assume you're testing without a load at the moment, but if you get it working make sure you have an adequate heatsink. These things are often more-limited by power dissipation (converted to heat) than by current alone.

...In case you don't already know this, power is calculated as Watts = Voltage x Current, and in this case it's the voltage dropped across the regulator. For example, if you feed 6V into the regulator there is 1V across it for 2W at 2A. But if you feed 12V into it that's 7V across it for 14W at 2A.

...Switching regulators are more complicated (and they need an inductor to store energy) but they are more efficient because the main-controlling transistor or MOSFET inside the chip is switching completely-on and completely-off so it never "sees" voltage & current at the same time. (Of course the switching is filtered/smoothed so you get constant DC out of the regulator.)