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Electronics and Electrical Engineering Design Forum

 

Passives

LDO heating up

Hi

I want to build a circuit like that shown in the picture. I haven’t assembled it yet, instead I have made a small test circuit for the LDO to measure its correct operation. I have noticed one thing, if I don’t apply the voltmeter terminals to the circuit, the LDO gets very hot with the danger of burning up. As you can see on my circuit, in the neutral switcher state the LDO doesn’t have any current consumer to convey its current to. The batteries will be all the time inserted, of course. Do I take a risk of burning the LDO?

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szymekwm@o2.pl
Asked By:
Simon Mak
1 year ago
 
 
{username}
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What’s the battery voltage?

Also, check to see that the LDO isn’t oscillating.

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{username}
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if your battery voltage is to high a big part of the energy is wasted as heat.

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{username}
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The battery voltage is 3×1,2V=3,6V. For the oscillation, wouldn’t be it beneficial for the LDO to oscillate with the capacitors in switcherless state, to dissipate the uncosumed power?

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{username}
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Maybe a stupid question, Are you sure that it is connected correct and not in reverse.
because you are at 80mA well in the 150mA limit and the voltage is good. And yes the capacitors are good.

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{username}
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Im inclined to agree with peter

Sounds to me as though your device is connected round the wrong way
The datasheet suggests a maximum of 4 to 18 volt maximum input defined as VI
The regulator in its on state at 4 to 18volt vi has a quiesant of 3ma , I OUT defined as 100 ma which is maximum current

I’m not sure if you have all 4 leds connected at once because your circuit neither show the junction to the diodes as a switch or permanent connection perhaps you could explain In fact it neither shows if on or off It appears as if you have a tri state switch with both pairs of leds off

With all 4 connected you would have 73ma that I can calculate in fact 76 ma if you account for 3 ma quiesant current

That’s near enough peak anyway which means the device is going to get extremely hot assuming your diodes are all on

You capacitance that you have used is ok ,peak bypass capacitance is stressed to be a max of 10uf so that’s fine

I would suggest change the Regulator myself for a far better solution

Secondly download and read the datasheet or possibly that Peter is correct

See below for specs

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{username}
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Ideally you want something like a ZSAT500C which will produce 5volts at 200ma then it will run cool
See below for datasheet

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{username}
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I have connected the test circuit correct, look at the board. But I did not use the capacitors in the test circuit, maybe that’s why the LDO was heating up. I would like to stay with 3,6V because of the portability and easy replacement of batteries (you can buy them at every news-stand).

Yes, it is a tri-state switch, with two groups of leds. So only two leds will be switched on at the same time, which yields a current of 43mA, which is half of the peak current.

Also, I have doubts, if the LE33CZ max output current is 100 mA (look at the title page) or 150 mA (page 9, specs for LE33C).

http://www.hobbytronics.co.uk/datasheets/LE33CZ.pdf

The resistor in the board is supposed to resemble a voltage meter.

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{username}
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Hi Simon Page 1 of your link says, quote “OUTPUT CURRENT UP TO 100 mA “ MAX

Page 9 Reads Output Current Limit this is when thermal and current protection kicks in In otherwords thoeretically the device shuts down resulting in a couple of millivolts out In otherwords current exceeding 100 and btw 150 the device starts shutting off non regulation occurs

150 ma in otherwords which should never happen if you are only running 43 ma there abouts Theoretically you aim for 100 ma max my friend not 150 ma In practice you aim for less than 100ma in order to keep operating tempartures down practically you aim for tops 60% of that figure You should never design to extremes unless apsolutley critical Worst scenario in otherwords

Could be because youve ommited caps You should include these I suspsect that might be an issue

Think logically here You wouldnt put a 15 amp cable where you intend to run 30 amps would you So why do that with a poor old regulator only capable of supplying at best 100ma Typically you would aim for besdt performance being 50ma Under fault conditions 100 ma not visa versa

If you ran the device at peak current The device runs max temperature The solder melts ouround the legs of the device and you wind up with dry joints No power out or intermittent

The difference between moving from design to technician and technician to design Now you know why I like apprenticeships self explanatory because fresh out of university has all the theory and know how and can design but practically is bloody useless He designs on books not knowing what the practical implementations of his / her design cause or how serviceable the product is

Now I’m making sense just like management Look at the mistakes they make why never worked from the ground floor up haven’t got a clue

Yes cost this country whole industries thats what they do and jobs and peoples lives and start wars

Just like cameron with his ideas on social security hasnt got a clue Not a clue similar to the newpaper advert this morning re hosuing for students and well pay you £200.00 a time without even so much as vetting the the people who are going to act as quote , “Host families “ ha ha !! poor bloody students thats all i can say , Havent got a clue what they are going to meet or come against “ Horror story 5 billion and one” , with a news paper salesperson for advertising with a couldnt care less attitude , quote Page 6 “The Royal Greenwhich Times “ Please contact Gaynor on 0208 89215033

Should read “wanted dead or alive I think “ thats if they get out of these places alive thanks to this stupid person

After all its all about the money !!

Good isnt it !!

Aha !! Eurika huh !!

Hope that helps you

Mark

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{username}
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Ok, I understand now, the max output current is 100mA. I think the capacitors are the reason for overheating, since I didn’t use them in the test setup. Thanks everyone for help.

 
{username}
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No worries Simon welcome !!

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{username}
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The bewares for both foreign and local students

See and advert like this make sure you contact them make sure you can reach both numbers take a note of the newspaper who’s advertising such so called golden opportunities, get references meet the people face to face and above all do a criminal record check if you have too Other wise you could very well lose your life particularly in this country

Yes I’m not pleased with this lot ether and had years of experiences in this country not to mention elsewhere in the world

I know only to well what some of these people who are “Host families” will get up too if not the social and domestic problems you will encounter often resulting in violence not just amongst themselves but also towards you if you happen to be there at the time Anything for a pound note some of them and I mean anything

None to pleasant I can assure you further if you see adverts such as this and the newspapers cant explain or wont answer report it for gods sake for other peoples saftey if not your own

So be warned and be ultra careful especially in the UK and abroad Its not worth the risk anymore

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{username}
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First of all you battery symbol as shown is Backwards, your battery as connected is on the output and not the input. Your LED circuits are on the inputs and appear as exact same circuits.

If you actually connected this per your schematic of course it isn’t working and surprised isn’t be used as a marshmallow roaster.

You need to correct something. Not surprised you are having trouble.

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{username}
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I didn’t spot that either straight away I wonder if he’s has learning problems swaps left and right , draws everything upside down

I wonder if he’s dyslexic fortunately though he has the caps round the right way , otherwise there would be a loud bang except of course for the first one which is non polarized but it is only a circuit diagram isn’t it ? Not the practical item put together so we don’t really know that he’s connected the battery round the wrong way in practice do we ?

And we also presume that all people have the same learning ability don’t we hence he might very well be quite clever , but cant put this onto paper

Has that occurred to you Earl See I suffer from this as well my mind locks up and I cant focus on anything , cant move sometimes , cant think straight although I know what I want to do and I now how to do it I just cant function,

I wonder if you saw that earl before you dished out your 50 lashes

A bit like my spelling at times unless I have help from office or direct to the net or a dictionary Lets face it who uses dictionaries anymore We don’t We use auto complete

But my programming is good and I did recieve lots and lots of punishemnt for not being able to do homework or so my superiors thought and I found science dead boring so much so that I slept right the way through classes at school but believe it or not I still managed to pass all six subjects including maths and science and another language , and managed distinctions for uni and for college and imanaged a diploma in law whuich was taught to me in two lanagauges which i had to speak and write and read and i managed to complete at least four programming langauges

I do have a certificate that catagorically says Im normal Not may people have that one do they and a certificate to say Im HIV free

Now all im waiting for is my dog tags to say Im dead

Good isnt it I must be the sixth wonder of the world

Only Eral Ive been like this since a child only this didnt dawn on me or anyone else till a lot later in life but im normal and can probabbly do thrice quadriple what you can do on one hand and I can show you what to do and a few others and I know exactly where your making mistakes Only Im considered abnormal after all Ive been in a mental assylum so accoding to society I must be nuts , untill they want something done Aaaah then its different of course hmmmm Interesting

Told you !! Don’t think sometimes do we hmmm !! Easy when you can only see in one direction with blinkers on bit like the population in Kent a bit like their horses a bit like their conservative party a bit blinkered , a bit blind , only want to see what they want to see and nothing else , very narrow minded when it comes to life in general Cant quite see themselves in the mirror at times can they !!

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{username}
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Go and have a look at the drawing again its drawn upside down EARL !!!!!!!!!

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{username}
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Normal or what you consider to be normal would draw his circuit as below

Right way round left to right he hasnt hes draw his upside down and right to left Hence his mistake on the
battery

See below In fact Im surprised he didnt draw the capacitors round the other way 2.2 uf on the supply in and ceramic on the output, “Interesting !”

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{username}
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Yes, it’s just a typo. In my test setup I have connected the power supply the right way, knowing that the plus is supposed to go to the LDO IN, that it is the power supply side. Below is the corrected layout, but there is nothing wrong with the leds.

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{username}
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Yes i thought as much Simon
Change the regulator Simon , much easier

 
{username}
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Well let’s just assume that you sort of have it connected correctly, that is an assumption, nothing else to go on. A likely scenario it that it is oscillating because I don’t see a load when the button is not pushed, i.e., LDO is unloaded. So what who cares no load. well depending on the caps in the circuit, under no load some linear regulators can oscillate. You can easily fix this by putting some minimal load, say a 10K Ohm on the regulator’s output voltage. The DVM that you are placing on the device when you notice it is cool, is sort of doing that, but it has a different impedance, none the less it appears to stop the oscillation.

Again the schematic is so bad (sorry if that offends) that I am just guess about how it’s actually connected.

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{username}
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In my test setup I didn’t use the caps – can oscillation still occur then?

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{username}
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In my experience I have not be able to get linear regulators to oscilate with the output caps removed. Now I want to preface my comment not using an output cap was not a study on all regulators and not having output caps. I removed mine for very specific reasons which goes beyond your project.

In any event just to make sure put the 10K Ohm resistor on the output and it should be fine (in most cases). Also the manufacturer usually have some info on output caps, types and min load. Resolving an oscillation is the easy part. You do need an input cap

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{username}
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Thank you, I have put the resistor to the output, after the caps. Should it be before or after the 2,2uF capacitor?

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{username}
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I would assume that not using the cap on the output can be the cause of oscillation, only because the manufacturer stipulates a 2.2uF cap on the output for “stability”. Also, if you are using the version with the inhibit, then ground it when not using to inhibit — i.e. don’t leave it floating (just in case).

Earl’s statement that he has never been able to get one of these to oscillate, is likely predicated on proper layout and such — who knows how you have your device “hooked-up” (no offense).

And, the 2.2uF cap should be as close to the regulator output pin as possible, with the negative side of the cap connected as close to the ground pin on the regulator as possible, and the input lines should be as far away from the output lines as possible. Also, avoid running ground current through the capacitor’s line to the regulator’s ground. Same with the caps positive line — run it as directly to the regulator’s output pin as possible.

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{username}
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I just noticed, when I put the load directly on the LDO output, then my voltage will drop a lot. Where should I place the additional load to stop oscillation?

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{username}
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If that 10K resistor is supposed to be your minimum load, then you need to connect it from the output of the regulator to ground.

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{username}
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Like that?

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