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Author Topic: Halogen Transformer Explanation of Circuit  (Read 3252 times)
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I have a halogen transformer for a light.    It does not work and I want to understand where it has broken down and address the issue.     On a high level, it was plugged in to 220 volts when set to 110.    However, it was designed to work @ 220 volts (when properly set).     Over the past month and a half, I have studied the traces, ordered replacement parts, but the problem may very well be in the transformer (which I'd like to re-wrap as a project, if needed).    Then again, the transformer only has 1 primary input....     I am at a loss as to what the circuit / traces are doing.   Hard to stare at something for this long and come up puzzled, can someone get me unstuck?

The AC input -  terminals  L  and N,   goto fuse, then ac/dc bridge.  The N terminal shoots past the bridge and to the 120/220 voltage selector wires - when the wires are shorted it sends power (110 volts) to 2 capacitors wired in opposite directions (why don't they blow up?) that meet up with the + and - side of the ac/dc bridge and 2 1/4 watt x 1M resistors.   When the voltage selector wires are not shorted, the unit is in 220 volt mode...  

After that, it seems to feed into some C5071 type things (transistors)  which I have no idea...  Finally, all that goes into the transformer  -  2 small copper wires - I assume that is the primary.    If it is AC  or DC at this point -  no idea.  I thought DC...

Please explain what is happening when the voltage selector wires are shorted together and why having them open makes any bit of difference.
What are the big orange Poly Capacitors for?
What are the transistors for?
Why are such little resistors ok?
Is this transformer taking AC or DC?
What is the lowest voltage I can test this transformer at?
Why the green filter/coil looking thing?
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The 12 volts is used for the fan to keep the transistors cool.
The LAMP output is 24 volts
There is an unused 24 volt tap
Bridge Diode Rectifier KBU808

Here are pics
(please save them to your hard-disk and ask for more if desired)
http://www.usbjunk.com/halogentransformer1-1.jpg
http://www.usbjunk.com/halogentransformer1-2.jpg
http://www.usbjunk.com/halogentransformer1-3.jpg
http://www.usbjunk.com/halogentransformer1-4.jpg
http://www.usbjunk.com/halogentransformer1-5.jpg
http://www.usbjunk.com/halogentransformer1-6.jpg
http://www.usbjunk.com/halogentransformer1-7.jpg
http://www.usbjunk.com/halogentransformer1-8.jpg
http://www.usbjunk.com/halogentransformer1-9.jpg

Many thanks for the sets of eyes
« Last Edit: January 24, 2014, 11:00:40 pm by Eddiie » Logged

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I think your webserver exploded.
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Fixed.
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On a high level, it was plugged in to 220 volts when set to 110.

It's cactus then.  You show the photos without the fuse - the fuse blew, didn't it?

ordered replacement parts

Really?  Which parts?  You might get away with replacing the 2SC5071 transistors, but the risk of other parts being damaged sufficiently to fail later suggests the obvious - waste-bin.

the problem may very well be in the transformer (which I'd like to re-wrap as a project, if needed).

Transformer will be fine.  It's the most robust component.

why don't they blow up

Transistors protected them by burning out and blowing the fuse.

Please explain what is happening when the voltage selector wires are shorted together and why having them open makes any bit of difference.

With the link out, it is a full wave bridge rectifier, charges the capacitors to 154 volts from a 110VAC supply, total 308V.  With the link in place,  it is a voltage doubler.  Doubling 220V makes a total of 616.

What are the big orange Poly Capacitors for?

Possibly "Snubbers" to absorb transients as the transistors switch at a supersonic frequency, or as below.

What are the transistors for?

Chopping up the 308V at a supersonic frequency into AC for the small transformer.

Why are such little resistors ok?

They were not overloaded.  Probably.   smiley-roll

Is this transformer taking AC or DC?

Transformers hate DC.  One (or both) of those big orange capacitors prevent the transformer from seeing DC.

What is the lowest voltage I can test this transformer at?

Whatever you like, as long as it is at a frequency exceeding 18 kHz.

Why the green filter/coil looking thing?

A filter coil?   smiley-zipper  No, it is the feedback transformer which makes the transistors oscillate.

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Your guess is as good as mine.
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Ah yes the fuse was blown!   It was also a 3 amp fuse, when the board calls for 2 amp.  Another bad sign.
I have put a 2 amp fuse in, applied 110 volts AC to this board and nothing happened.    The lights in the house dimmed for a split second while the current rushed in, the fuse did not blow.   The light bulb did not light.   The bulb is good.

The replacement parts I ordered are everything on the board pretty much -
Starting with the bridge rectifier KBU808  (in the mail)
Next in line, tested the 1M resistors - they are ok
Next the 220uf 200 volt caps (in the mail)
Next the Polycaps  400v 1.5uf  (in the mail)
Next some other resistors - forget the values but they tested ok
Next is 2 small poly caps  0.01uf 630 volts  (in the mail)
Then things rotate 90 degrees - starting with the DB3 diac trigger diode (in the mail)  What does this do?
1R5 resistors, replaced!
the Diodes test OK.  That is, I get nothing on the volt meter when probes connected one way, and something registers when reversing.
The last piece is the C5071 transistors, replaced!

The only 2 things on here I do not have the knowledge to replace is this filter coil oscelator thing you call a feedback transformer and the transformer.
The transformer I would actually like to rewind if needed.  I think it would be a fun thing to do.   
Testing the transformer the only way I know how using a volt meter, I get 0.10 ohms on the lowest setting.
Connecting the volt meter to the other coils and sending 12 volts DC in, I can get results for a brief moment on the voltmeter.
I think it is good.   Your comment about it being the most robust piece also reassures my conclusion.

The parts are being replaced as they arrive.  Therefore, pretty much everything will wind up being replaced and no need for the waste bin.  Right?

I've removed these components from the board and tested myself, they seem to work but will replace anyway.  That is, the C5071 transistors I connected 12 volts DC was getting 12 on the volt meter.     Maybe that is a direct short?
I noticed these transitors although connected to the frame for heatsinks they had protective material between them.  Does this mean the backs are live and I should not touch?    The replacements have a black backing and feel more plastic than metal, is this possible?

Have not ordered the diodes, should I?

Looping back to the voltage selection wires -
Ok now this scares me.
Quote
With the link out, it is a full wave bridge rectifier, charges the capacitors to 154 volts from a 110VAC supply, total 308V.  With the link in place,  it is a voltage doubler.  Doubling 220V makes a total of 616.

The freaking light bulb is only 24 volts!!!  Perhaps this is a bust of energy to ignite the halogen gas on startup?
Understanding what you're saying and looking at the traces. With the link out (220 volt mode), only the bridge rectifier is active which adds 220uf to the other 220uf passing it on through to one C5071 transistor then my head starts to spin following what happens next.

When the link it together (110 volt mode), I still lose what happens.   There is a trace from the N side of the AC input to the 220uf caps.  Crazy stuff.    I have note ventured too far into waves or clocks yet.  Perhaps this is what I am missing and why it is not making sense.  Thank you for your time and explanation.

Why are we at 308v now?   That bulb is 24 volts!    This 308v gets fed into the transformer?   What is the purpose of the transformer then?     Why take such large inputs?  Why step them up?     For ignition, right?

I knew transformers hated DC, but thought this was an exception since it was coming from the rectifier.  Pretty sure the transformer is fine.  How those big orange caps stop the transformer from seeing DC is something I'd like to learn  I could use  this idea in other things.

Thanks again!
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Ah yes the fuse was blown!   It was also a 3 amp fuse, when the board calls for 2 amp.  Another bad sign.
I have put a 2 amp fuse in, applied 110 volts AC to this board and nothing happened.    The lights in the house dimmed for a split second while the current rushed in, the fuse did not blow.   The light bulb did not light.   The bulb is good.

One might worry about the lights flickering, but it suggests the bridge rectifier and capacitors are working.

Likely the transistors - one or both - are open circuit then.

The replacement parts I ordered are everything on the board pretty much -

I am quite sure it would be cheaper - far cheaper - to buy a new module.  Nevertheless ...

the Diodes test OK.  That is, I get nothing on the volt meter when probes connected one way, and something registers when reversing.

Sounds good.

The last piece is the C5071 transistors, replaced!

I thought you could not find data on them?  I am fascinated you could order them without knowing what they were.

The transformer I would actually like to rewind if needed.

I doubt it.

  I think it would be a fun thing to do.   

Messy.

The parts are being replaced as they arrive.  Therefore, pretty much everything will wind up being replaced and no need for the waste bin.  Right?

But you will still have a number of old parts of dubious reliability.

That is, the C5071 transistors I connected 12 volts DC was getting 12 on the volt meter.     Maybe that is a direct short?

Not sure exactly how you are describing testing them.

I noticed these transitors although connected to the frame for heatsinks they had protective material between them.  Does this mean the backs are live and I should not touch?    The replacements have a black backing and feel more plastic than metal, is this possible?

Some transistors have integral insulator, most do not.  I would include it if it was previously there.  Unlikely to have been damaged by the overload as such, but you need to be mechanically careful with it.

Have not ordered the diodes, should I?

Don't know - haven't studied where they are involved in the circuit.

Ok now this scares me.

It should.

The freaking light bulb is only 24 volts!!!  Perhaps this is a bust of energy to ignite the halogen gas on startup?

This thing is after all, a "transformer" and the bulb is a filament bulb, not a discharge tube.

In normal operation, each capacitor is charged to the peak of 110 volts, which is 154.  Together they total 308.  The two transistors chop this into a square wave whose peak-to-peak amplitude is 307, thus its amplitude from the middle is in fact 153 again.  This is now fed into the transformer which "transforms"  it down to 24 V.  Note that what the bulb gets is high frequency AC - not DC.

Understanding what you're saying and looking at the traces. With the link out (220 volt mode), only the bridge rectifier is active which adds 220uf to the other 220uf passing it on through to one C5071 transistor then my head starts to spin following what happens next.

In this mode, the two capacitors are in series so they share the 308 volts.  The transistors "chop" alternately from one end of the capacitors to the other.  The transformer is connected (through the polycaps I gather) to the midpoint of the 308 volts.  The polycaps are (I gather) used as the electrolytics don't particularly like the high frequency current.

When the link it together (110 volt mode), I still lose what happens.   There is a trace from the N side of the AC input to the 220uf caps.  Crazy stuff.    I have note ventured too far into waves or clocks yet.  Perhaps this is what I am missing and why it is not making sense.  Thank you for your time and explanation.

With the link in place, one side of the supply is connected to the midpoint of the two caps.  The other side charges one cap on the positive swing and the other on the negative, using only half of the diodes in the bridge; the other half just stays reverse biased.  So each charges to 154 volts.

Why are we at 308v now?   That bulb is 24 volts!    This 308v gets fed into the transformer?   What is the purpose of the transformer then?

It transforms!   smiley-eek

Why take such large inputs?

Because that's what the mains voltage is.

Why step them up?

Because that is the peak of the sine wave.  That's what happens when you charge a capacitor with a rectifier.

How those big orange caps stop the transformer from seeing DC is something I'd like to learn  I could use  this idea in other things.

A capacitor in series prevents DC from flowing.
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I will update this thread after the parts come in.
The big poly caps are coming today.
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Hello,

The big fat poly caps came in today but they are smaller than the old one's.   Are they still OK to use?  Same numbers as the old one's -  CBB22 440v  155J

Does size matter?     smiley-confuse

Last parts coming in tomorrow!

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Here's an update -

Plugged the thing in after replacing almost every part.   It works!   That is, the 12 volt output starts at 19 volts then stabilized at 17 volts. (??)  Close enough, right?  After removing power, the voltmeter stayed on 17 volts for a few minutes until I connected a load (a fan) to drain it.

Connecting the voltmeter to the LAMP outputs and powered up again - I got 0.20,   then realized it is probably AC so switched the voltmeter to AC and got 0.00

Odd.

Why not connect the bulb to the power supply and just see what happens.    OK!

Connect the lamp, power on, POP!  a flash of light!  But not from the bulb --  No, it was from one of the C5071's blowing up.

See picture of the aftermath..
http://www.usbjunk.com/halogentransformer1-10.jpg

Any idea why this happened?   Could it be the wrong 'type' of C5071's?    I think maybe so.
Here is a picture of one of the old one's (middle)
http://www.usbjunk.com/halogentransformer1-11.jpg

Another look at the traces on the bottom of the board -
http://www.usbjunk.com/halogentransformer1-12.jpg

Why connecting the bulb would make the C5071 blow?

The 2 amp fuse (actually circuit breaker) did not blow.
« Last Edit: January 31, 2014, 11:53:00 pm by Eddiie » Logged

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It may be the lighting but do you have some solder shorts across a couple of tracks?
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Sorry, but it seems to me that you are "flogging a dead horse"!

It is all a bit tricky.  Now that you mention it, I note that it has both an AC output to your lamp - direct from the transformer - and a rectifier to generate a DC voltage which you say gives 19V.  Just what sort of halogen lamp device was this supposed to operate?

The AC generated is at a supersonic frequency, which a common multimeter may not be designed/ rated to measure.

My advice from the start was that you cannot readily know just what cascade of failures has occurred, so I (tend to) consider any such failed switchmode power supply a "write off" and surely it would be cheaper to obtain a new unit?  Clearly the stress of the load has caused something to happen by way of an overload, but I am unable to predict what.

Nor have I studied the soldering.  smiley-zipper
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Alrighty!  Ordered more parts.  In this round of parts order I replaced all diodes and resistors.

Now everything has been replaced except -
Transformer
Flyback Oscillator thing
Power connectors
Fuse holder


Everything else has been replaced.   Also cleaned up the traces on bottom.  Did not find any shorts.

http://www.usbjunk.com/halogentransformer1-13.jpg
http://www.usbjunk.com/halogentransformer1-14.jpg
http://www.usbjunk.com/halogentransformer1-15.jpg

Will plug it in tomorrow.

This Halogen Transformer cannot be replaced, they do not make this model any more.  By replacing every component, in essence I have replaced it?
« Last Edit: February 08, 2014, 04:12:07 am by Eddiie » Logged

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To me, that transformer looks like it overheated, and has likely failed (probably due to the 3A fuse being used). I wouldn't trust it, and it is likely what has failed.
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Yeah, you could be right.   I have no problem removing the transformer (again) and testing separately.
Just not sure how to test it.

I guess I can remove the transformer from the circuit board, take a power reading at where the transformer would get its power from and test it separately using a light bulb as a fuse.   Not having done this before what is the expected behavior?  Possibly If the bulb stays lit, there is a short..  60 watt bulb = 1 amp?

I assume all these caps, transistors and diodes is to deal with the 2 different AC input voltages?

If the board does not blow up with the transformer removed, it'd be a safe bet the transformer is the problem?  Especially now that everything has been replaced.   It would confirm no shorts, and correct parts - mostly.

Any guesses what I will see at the transformer input?  I'd guess 110, but reading the responses on this post it should be more like 300?  Or 300 divided by 2.

This seems to be a better approach.
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Wah wah

http://www.usbjunk.com/halogentransformer1-16.jpg
http://www.usbjunk.com/halogentransformer1-17.jpg

No load.

Same thing, and worse.   Not only did the same C5071 blow but a 220 resistor and a green ploy cap blew.  The Poly caps do not care about polarity, right?

Fuse did not blow, only shot about 1 second worth of 110V AC...   Not long enough to register anything on my voltmeter (which was connected to the black/white wires on the picture)

I can't tell if the diodes blew or not.

What in the heck is making the C5071 blow?   

I was expecting it to work.  heh

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