Prev: Does anybody make a micro with 3 DACs
Next: Optocoupler question....
From: Robert Baer on 23 Apr 2010 02:46
Joerg wrote:
> Hammy wrote:
>>
>> I wound a toroid to use as a HS gate drive transformer for a 100W two
>> switch flyback. I'm using the typical DC restore technique AC couple
>> the transformer.
>>
>> Here's my schematic;
>>
>> http://i42.tinypic.com/9gvyow.png
>>
>> I'm using a PIC and a FET driver to simulate the extremes of the PWM
>> controller duty cycle and drive level and it works well with the
>> exception of Burst Mode. Burst mode is when the controller modulates
>> the original gate signal at light load for anyone who doesn't know.
>> A picture is worth a thousand words.
>>
>> Here's my gate waveform at 90kHz 70% duty. A little sloping but
>> acceptable.
>> http://i39.tinypic.com/25kieyq.jpg
>>
>> Now here's where the fun begins I'm modulating the 90kHz to simulate
>> burst mode.
>>
>> http://i44.tinypic.com/qy5l69.jpg
>>
>
> Ah, another guy with an Instek scope.
>
>
>> Here's a zoom of one of the burst.
>>
>> http://i43.tinypic.com/2eumxbk.jpg
>>
>> My primary and secondary are 1:1 ; inductance of 1.5mH.
>>
>> Is there anyway to clean this up?
>
>
> Looks like you haven't wound your toroid transformer in bifilar fashion.
> That is essential for apps like this, leakage inductance must be
> minimized, else this rings like crazy.
>
For really excellent fast pulse transfer, use coax cable - use the
shield for the primary and the center for the (HV) secondary.
It is a bit messy, but the shield can be split a number of times for
input one-turn equivalent via paralleling...
From: Jan Panteltje on 24 Apr 2010 05:39
On a sunny day (Fri, 23 Apr 2010 14:13:56 -0700 (PDT)) it happened
"langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote in
<7a067e90-7964-40dc-bf79-59c3fa6323fe(a)c21g2000yqk.googlegroups.com>:

>There's also something like the ADuM6132,- supply,isolation and driver
>in one.


That is very nice, and not even expensive.
From: JosephKK on 28 Apr 2010 08:52
On Fri, 23 Apr 2010 10:48:28 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>Hammy wrote:
>> On Fri, 23 Apr 2010 09:24:53 -0700, Joerg <invalid(a)invalid.invalid>
>> wrote:
>>
>>
>>> With a flying source that's a problem because the Instek connects the
>>> probe shield to PE. So you get ground loops and tons of ringing. Plus
>>> you neighbors listening to AM radio won't be very happy about that. You
>>> can get battery packs for many Instek models but it's very expensive. I
>>> never checked whether one can hack into this and connect one's own
>>> battery. Even then you'd at least need to wrap the probe through a nice
>>> big ferrite a few times.
>>
>> Yep they defiantly aren't giving the battery option away.
>>
>
>Another old trick is to use a car battery and inverter. Mine just
>croaked. Couldn't believe it, half a year ago it was showing slight
>signs of weakness but would still crank a 2.6l gasoline engine alright.
>So I replaced the one in the car. When I needed it for isolation
>purposes a month ago ... nada, zip, zilch. It was totally hi-Z, charger
>went to 17V and shut off, and the battery wouldn't even light a 1W bulb.
>Puzzling how it could have gone so fast.
>
Sounds like electrolyte dry out. See if you can find a way to "juice"
the cells again.
>
>>> Maybe at your frequency range you could try a diff measurement with two
>>> channels.
>>>
>>>
>>>> I don't think its possible to do this without a floating supply and
>>>> using an opto to send the HS control signal to a driver. Even if I
>>>> disable the burst mode the controller could still go into burst mode
>>>> under fault condition like over current. To many chances something
>>>> could go wrong.
>>>>
>>> With properly size caps it should be possible.
>>
>> I haven't given up yet I'll play around with what I have part wise and
>> see if I cant get something reliable.
>>
>
>Try to find some smaller ones, maybe from EMC filters :-)
>
>
>>>> I suppose I could use an old UC384X it has none of these fancy
>>>> features and a 0.5 duty cycle clamp. Other then the unpredictability
>>>> of the burst mode it does work well.
>>>>
>>> Question: Since this is a flyback why is the source flopping about?
>>> What's it doing? Maybe post the whole schematic if it isn't confidential.
>>
>> No not confidential I haven't made up a full schematic yet. :-)
>>
>> Here's my actual test schematic. I'm not showing Bypass caps and the
>> lm317 for the driver and the 78l05 for the PIC both regulators get
>> their input from the 20 V supply V1.
>>
>> http://i39.tinypic.com/1zf4gpl.png
>>
>> That is just a test set-up to test the high side drive for a active
>> clamp flyback shown below.
>>
>> http://i39.tinypic.com/10s7ybl.png
>>
>
>Since it can't bang past either rail you cold probably bootstrap that.
>But transformers are a good option here, just not with 0.1uF in series.
>
>
>> I don't have a schematic for the flyback because I just started
>> considering it yesterday. I'm just working out how to drive the
>> High-side FET.
>>
>
>No chance just to do a half-bridge and be done with it? It would also be
>a bit easier EMI-wise. And no air gap.
>
>>
>>>> I was also planning on using synchronous rectification a shottky
>>>> dissipates 4W but this FET would have less then 1W conduction losses.
>>>> I thought I would try something different;-)
>>>>
>>>> http://www.nxp.com/documents/data_sheet/PSMN8R2-80YS.pdf
>>>>
>>>> They are coming out with some nice FETS.
>>>
>>> But you have to drive over 3500pF of gate capacitance. Make sure the
>>> Rdson versus gate capacitance deal is somewhat optimized for the chosen
>>> frequency and power level. Ideally the losses due to both effects would
>>> be about on par.
>>
>> A two amp driver should take care of that. I've just been using a
>> spreadsheet from On semi for rough estimates for now.
>>
>
>Yes, 2A would be plenty.
>
>
>>> It's pretty brazen that they advertize this as a 130W device. I wonder
>>> what it's lifetime will be under that sort of load (in milliseconds,
>>>from turn-on to a sharp popping noise).
>>
>> They all do that it seems worse now because of the high 100 plus amps
>> they also quote for the part.
>
>
>The topper is what I saw in some discount store aisle. An audio
>amplifier in a blister pack, very ritzy packaging. It claimed 1000 (!)
>watts PMPO and the power supply was <gasp> a wall wart. Yeah, right ...

Oh yes, I remember Peak Meaningless Pretend Output from the 1960s. A
play value created by inventive misapplication of theory that cannot be
duplicated in the real world. And look at the thin cord that carries it
from the wall wart to the device, better than room temperature
superconductors it must be.
From: Joerg on 28 Apr 2010 11:08
JosephKK wrote:
> On Fri, 23 Apr 2010 10:48:28 -0700, Joerg <invalid(a)invalid.invalid>
> wrote:
>
>> Hammy wrote:
>>> On Fri, 23 Apr 2010 09:24:53 -0700, Joerg <invalid(a)invalid.invalid>
>>> wrote:
>>>
>>>
>>>> With a flying source that's a problem because the Instek connects the
>>>> probe shield to PE. So you get ground loops and tons of ringing. Plus
>>>> you neighbors listening to AM radio won't be very happy about that. You
>>>> can get battery packs for many Instek models but it's very expensive. I
>>>> never checked whether one can hack into this and connect one's own
>>>> battery. Even then you'd at least need to wrap the probe through a nice
>>>> big ferrite a few times.
>>> Yep they defiantly aren't giving the battery option away.
>>>
>> Another old trick is to use a car battery and inverter. Mine just
>> croaked. Couldn't believe it, half a year ago it was showing slight
>> signs of weakness but would still crank a 2.6l gasoline engine alright.
>> So I replaced the one in the car. When I needed it for isolation
>> purposes a month ago ... nada, zip, zilch. It was totally hi-Z, charger
>> went to 17V and shut off, and the battery wouldn't even light a 1W bulb.
>> Puzzling how it could have gone so fast.
>>
> Sounds like electrolyte dry out. See if you can find a way to "juice"
> the cells again.


Strange thing is, the fluid level inside is ok. It's one of those
supposedly maintenance-free ones but one can pry off the lid assembly to
peek inside.

Why is it that this brand name battery is dead after 5-6 years, the gel
cell in my StatPower emergency kit also died after 5-6 years, while the
gel cell in my over 10 year old big $10 Chinese flashlamp is still fine?

[...]


>> The topper is what I saw in some discount store aisle. An audio
>> amplifier in a blister pack, very ritzy packaging. It claimed 1000 (!)
>> watts PMPO and the power supply was <gasp> a wall wart. Yeah, right ...
>
> Oh yes, I remember Peak Meaningless Pretend Output from the 1960s. A
> play value created by inventive misapplication of theory that cannot be
> duplicated in the real world. And look at the thin cord that carries it
> from the wall wart to the device, better than room temperature
> superconductors it must be.


They probably rely on the fact that the majority of shoppers does not
have an engineering degree :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Grant on 28 Apr 2010 16:43
On Wed, 28 Apr 2010 08:08:06 -0700, Joerg <invalid(a)invalid.invalid> wrote:

>JosephKK wrote:
>> On Fri, 23 Apr 2010 10:48:28 -0700, Joerg <invalid(a)invalid.invalid>
>> wrote:
>>
>>> Hammy wrote:
>>>> On Fri, 23 Apr 2010 09:24:53 -0700, Joerg <invalid(a)invalid.invalid>
>>>> wrote:
>>>>
>>>>
>>>>> With a flying source that's a problem because the Instek connects the
>>>>> probe shield to PE. So you get ground loops and tons of ringing. Plus
>>>>> you neighbors listening to AM radio won't be very happy about that. You
>>>>> can get battery packs for many Instek models but it's very expensive. I
>>>>> never checked whether one can hack into this and connect one's own
>>>>> battery. Even then you'd at least need to wrap the probe through a nice
>>>>> big ferrite a few times.
>>>> Yep they defiantly aren't giving the battery option away.
>>>>
>>> Another old trick is to use a car battery and inverter. Mine just
>>> croaked. Couldn't believe it, half a year ago it was showing slight
>>> signs of weakness but would still crank a 2.6l gasoline engine alright.
>>> So I replaced the one in the car. When I needed it for isolation
>>> purposes a month ago ... nada, zip, zilch. It was totally hi-Z, charger
>>> went to 17V and shut off, and the battery wouldn't even light a 1W bulb.
>>> Puzzling how it could have gone so fast.
>>>
>> Sounds like electrolyte dry out. See if you can find a way to "juice"
>> the cells again.
>
>
>Strange thing is, the fluid level inside is ok. It's one of those
>supposedly maintenance-free ones but one can pry off the lid assembly to
>peek inside.

Sulphation, do the plates look white? High impedance batteries due to
sulphation can be recovered, hardly worth the effort though as the success
rate has been reported as low as 30%. Leave it at 17V for a long time,
or get one of those pulse/spike units that are supposed to break down the
sulphate.

Car batteries often are used in a chronically undercharged state due
to short trips, and if you happen to have a regulator at low end of the
loose spec auto range.

Since you took the lid off, try adding some battery restorer? Try some
phosphoric acid -- some web searching will hint at the dosage. I've only
read about this acid, not tried it.
>
>Why is it that this brand name battery is dead after 5-6 years, the gel
>cell in my StatPower emergency kit also died after 5-6 years, while the
>gel cell in my over 10 year old big $10 Chinese flashlamp is still fine?

5-6 years is an okay life for car battery, design life is 4 years.

Poor charging techniques, old fashioned charging regimes that didn't get
updated with the newer battery technology?

Grant.
--
http://bugs.id.au/
First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: Does anybody make a micro with 3 DACs
Next: Optocoupler question....