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'[EE] boost buck DC/DC, efficiency drop 30% and hea'
2010\07\08@151141 by microsoftwarecontrol

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part 1 320 bytes content-type:text/plain; (decoded quoted-printable)

Using TI boost buck, in boost mode. it is unsteady, some time heating up
and take almost double amount current. Output V is fine and out current is always near 1 A. Just input I, sometime increasing for unknown reason to me.

Any one knows what it is and how to fix it?



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2010\07\08@152458 by Mark E. Skeels

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part 1 422 bytes content-type:text/plain; charset=GB2312 (decoded 7bit)

Guessing some kind of oscillation?

Mark


microsoftwarecontrol wrote:
> Using TI boost buck, in boost mode. it is unsteady, some time heating up
> and take almost double amount current. Output V is fine and out current is
> always near 1 A. Just input I, sometime increasing for unknown reason
> to me.
>
> Any one knows what it is and how to fix it?
>
>  


part 2 35 bytes content-type:text/plain; charset="us-ascii"
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2010\07\08@161743 by Richard Prosser

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Inductor satutating / shorted turn ?

RP

2010/7/9 Mark E. Skeels <spam_OUTmskeelsTakeThisOuTspamcompetitionelectronics.com>:
{Quote hidden}

> -

2010\07\08@162134 by Bob Blick

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On Thu, 8 Jul 2010 15:11:33 -0400, "microsoftwarecontrol" said:
> Using TI boost buck, in boost mode. it is unsteady, some time heating up
> and take almost double amount current. Output V is fine and out current
> is
> always near 1 A. Just input I, sometime increasing for unknown reason
> to me.
>
> Any one knows what it is and how to fix it?
>

Are you using an approved type of inductor? Because what pops into mind
is that your are transitioning to continuous mode and the quick
inductance drop puts you in and out of a parasitic state of loop
instability. You can either use a bigger inductor of the same type, or
go to one that is more forgiving with continuous DC.

Cheerful regards,

Bob

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2010\07\08@163122 by Mark E. Skeels

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Could check this by raising or lowering the amperage load and see if the
problem stabilizes.

I think you should also be able to see the output of the switch go from
discontinuous  (ringing on turn off) to continuous if this is happening.

Mark

Bob Blick wrote:
{Quote hidden}

2010\07\08@163204 by Olin Lathrop

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Bob Blick wrote:
> Are you using an approved type of inductor? Because what pops into
> mind is that your are transitioning to continuous mode and the quick
> inductance drop puts you in and out of a parasitic state of loop
> instability. You can either use a bigger inductor of the same type, or
> go to one that is more forgiving with continuous DC.

Hmm.  Continuous mode should have lower peak current than discontinuous
mode, and therefore less likely to hit inductor saturation.  However, the
loop conpensation requirements could well be different between the two
modes.  If your loop is highly tuned that could be a problem.


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2010\07\08@173016 by jim
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You don't say whether this is an isolated output or not, but if it is,
check the feedback circuit for ground loops if not optoisolated.

Also, a large value cap on the input to the regulator has worked for us in
the past.


Regards,

Jim





{Original Message removed}

2010\07\09@022424 by RussellMc

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> Using TI boost buck, in boost mode. it is unsteady, some time heating up
> and take almost double amount current. Output V is fine and out current is
> always near 1 A. Just input I, sometime increasing for unknown reason
> to me.

> Any one knows what it is and how to fix it?

I'm surprised, after the very extensive amount of discussion on list
over a long period of time, that you don't try to do a better job of
explaining your problem.

It would be about as easy to give the IC type as to say "TI boost
buck" - and you are going to have to tell people this in due course.*
[* -  unless the problem is trivial.]

You are going to have to show people the actual circuit in detail,
along with load driven, input voltage, output voltage, general
environment etc* . Why not do this now and save the effort of people
having to ask you endless questions?

What is needed is a detailed explanation of what you are trying to do,
what key components you are using (at least IC and inductor, possibly
much more), what circuit, etc. Some idea of what you have tried, what
you know about such circuits, how you are measuring it and what
equipment you have available would also almost certainly help.

What is happening may depend very very very very substantially on the
answers to the above questions. Your circuit "topology" is NOT just
"boost". You will probably have some form of feedback. This may be
voltage mode, current mode, multiple loops or ???. In some modes,
operating above 50% duty cycle will cause unstable operation unless
you add an error signal proportional to clock ramp into the current
sense input. If your system operates around the 50% dc point it may
jump in and out of stability. Does this affect your circuit? Are you
operating at around 50% DC? How can anyone know if you do not provide
enough details?

Please help us help you and  provide a circuit diagram, part number,
operating conditions, load, how measurements are made, what major test
gear you have, what you know (brief summary), what you have tried, ...


                             Russell

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