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rudy.leurs
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35 kHz Oscillator

12/01/2009 8:01 AM

This is a PCB taken from an existing oscillator. The oscillator is broken.

Can anyone tell me what type of oscillator this is ? (Colpitts ?)

What is the meaning of D9 / D7 (protecting the transistor T1 ? )

Is D5 not in the wrong direction ? no current will flow through the pad R3 / R4 / L2 / C4.

I measured about 500Vac 35kHz at the output of transformer L2 is this correct ?

It looks to me some kind of push - pull configuration, but I don't see how it is working.

Thanks for any help.
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Pathfinder Tags: oscillator piezzo
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stoney
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#1

Re: 35 kHz Oscillator

12/01/2009 10:38 PM

Its a bit hard to see at that size but base drive for the transistors comes from windings off the output transformer. As the transformer is driven by either transistor its base will be driven by the approriate winding. The other winding will be oppsoite polarity and so the base is not broken down by a reverse voltage then the diodes you queried (d4?) will turn on and limit the reverse voltage. The transformer will saturate at a certain current and the base drive current will cease and the transistor will start to turn off. At this point the other transistor will start to be switched on by the reversed winding.

gotta go .. more later .. look up CFL schematics for similar operation.
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Anonymous Poster
#2

Re: 35 kHz Oscillator

12/02/2009 12:41 AM

Please post a larger clearer diagram; or a link to such, perhaps.

Thanks,

--- Rob
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Haajee
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#3

Re: 35 kHz Oscillator

12/02/2009 4:23 AM

It seems to be a self-oscillating Push-pull Power Oscillator normally used as DC to AC power converter.
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Randall
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#4
In reply to #3

Re: 35 kHz Oscillator

12/02/2009 5:52 AM

Yes, but what perplexes me is that there is no energy storage/smoothing after the initial rectifier.

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Haajee
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#9
In reply to #4

Re: 35 kHz Oscillator

12/02/2009 7:03 PM

GAs for posts #5, 6 & 8 for putting good drawings.

I suggest if more wide PIX are flipped vertically & saved as new and saved one be attached a better view can be in-line

See below the original one:

the later one
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Haajee
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#10
In reply to #4

Re: 35 kHz Oscillator

12/02/2009 7:17 PM

Add to my post#9

C4 & 5 1μF are filter capacitors

Seems to be low but see the load ....
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stoney
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#11
In reply to #4

Re: 35 kHz Oscillator

12/02/2009 10:24 PM

obviously the device is an ultrasonic cleaner .. maybe having the 100/120 Hz ripple is a bonus when it comes to cleaning or simply makes no difference.

so cost saving and probably long term reliability being the most important aspects.

I'm curious regarding the op's post, the oscillator 'is broken' but yet he has 500Vac at 35kHz at the output of L2 .. which is it ?

I'm just thinking that maybe the piezo elements have failed.
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Haajee
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#13
In reply to #11

Re: 35 kHz Oscillator

12/03/2009 3:39 AM

Please see my post #12

regards & a GA
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rudy.leurs
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#5

Re: 35 kHz Oscillator

12/02/2009 8:29 AM
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rudy.leurs
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#6

Re: 35 kHz Oscillator

12/02/2009 9:12 AM
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rudy.leurs
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#7

Re: 35 kHz Oscillator

12/02/2009 9:13 AM

How do I put a nice picture on your site ?
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rudy.leurs
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#8

Re: 35 kHz Oscillator

12/02/2009 12:51 PM
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Haajee
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#12

Re: 35 kHz Oscillator

12/03/2009 3:32 AM

It is a comlimentary-Symmetry Push-Pull circuit, which requires +/0/- supply

D9/D7 are shunted by zener diodes which means that Vce be maintained [pulse] -0.7V +V= Vzener

Complete description can only be worked out in a test circuit with CRO.

Hope of some info.
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