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Old 31st July 2008, 11:27 PM   #1
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Default Phase shift smps topology

Hi

I was wondering if I could build a phase-shift smps like this:
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Old 1st August 2008, 06:09 AM   #2
areza is offline areza  Bangladesh
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why not try UCC3895 ??!!
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Old 1st August 2008, 08:39 AM   #3
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When I want to understand and learn, I try to build things from the most basic components. Using an specialized IC (hard to get in my country btw) and use modified circuit from the datasheet I won't learn much.
Have you analysed my schematic?
I tried to generate phase shift operation by T-flipflops triggered from rising/falling edges of normal PWM stage. Is it the right way?

Regards
Adam
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Old 1st August 2008, 03:28 PM   #4
areza is offline areza  Bangladesh
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the schematics you shown is not a phase shift operation , cos one flip flop dont know the state of other flip flop,

check out UCC3895 data sheet timing and block diagram (page 7,8) , you may get the idea,
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Old 2nd August 2008, 12:35 AM   #5
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It's simple to do with a 74C14 CMOS Schmitt trigger inverter chip. The 330pF capacitor isn't needed. The phase shift resistor can be replaced with a small signal isolation transformer for feedback. Or you could use a bidirectional optocoupler. Another option is to place a standard optocoupler inside a bridge rectifier composed of 1N4148 diodes so that it experiences DC even though the phase shift circuit is AC.
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Old 2nd August 2008, 05:29 PM   #6
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Quote:
Originally posted by areza
the schematics you shown is not a phase shift operation , cos one flip flop dont know the state of other flip flop,


The flipflops are 'set' at start-up at the same time and one flop toggles at the risng edge while the second toggles at the falling edge of PWM signal .
So there is a phase shift between two half-bridges equal in time with pulse width from the compataror.
How should it be different from what ucc3895 generates?


Electrone

I don't understand, the circuit from the attachmet seems to generate constant phase shift. Could you explain please?


Regards,
Adam
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Old 3rd August 2008, 09:44 AM   #7
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Quote:
Originally posted by darkfenriz



The flipflops are 'set' at start-up at the same time and one flop toggles at the risng edge while the second toggles at the falling edge of PWM signal .
So there is a phase shift between two half-bridges equal in time with pulse width from the compataror.
How should it be different from what ucc3895 generates?


Electrone

I don't understand, the circuit from the attachmet seems to generate constant phase shift. Could you explain please?


Regards,
Adam
Hello Adam

To use feedback from the output to vary the phase shift, replace the phase shift resistor with some type of AC feedback device like an optocoupler with FET output that works well with AC.

The phase shift resistor is the unmarked one between the two Schmitt trigger components.

Also, in my real circuits, I find best results if the phase shift capacitor has a value ranging from 1nF to 10nF. I usually use either 1nF or 10nF. 220pF shown in the diagram may prove too small. The value of that capacitor needs to be much greater than the parasitic capacitance that the output side of the feedback device has.
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Old 3rd August 2008, 11:44 AM   #8
areza is offline areza  Bangladesh
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a very nice phase shift indeed

below a primitive simulation
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Old 4th August 2008, 02:26 PM   #9
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What is the problem?
difference between Q1 and Q2 after rectification is exactly CLK input signal.
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Old 4th August 2008, 06:28 PM   #10
areza is offline areza  Bangladesh
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no problem untill u try it with a proto,
thunder, light, magic and smoke
serious now, let me know the result, i m really interested,

good luck
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