Push Pull

bellx · 23rd January 2004, 07:37 PM

Why is the push pull topology not used in offline smps? I see mostly half bridge , full bridge and flyback. Can somebody explain ?

bellx · 24th January 2004, 02:29 PM

Surely somebody can answer?

subwo1 · 25th January 2004, 02:21 AM

One big reason is that it does not work well with ungapped transformers because of the tendency to apply magnetic offset to the trasformer core. Since the half bridge drives the transformer through a capacitor, any DC component in the pwm waveform is blocked.

djk · 25th January 2004, 10:59 AM

Push-pull also requires double the voltage ratings on the switch transistors.

For off line 240V the high voltage FETs have too much loss due to RDS.

IGBTs may be used with less loss, but they are not quite as fast.

23rd January 2004, 07:37 PM	#1
bellx diyAudio Member Join Date: Dec 2003 Location: KZN	Push Pull Why is the push pull topology not used in offline smps? I see mostly half bridge , full bridge and flyback. Can somebody explain ? __________________ I need more power!

24th January 2004, 02:29 PM	#2
bellx diyAudio Member Join Date: Dec 2003 Location: KZN	Nobody? Surely somebody can answer? __________________ I need more power!

25th January 2004, 02:21 AM	#3
subwo1 diyAudio Member Join Date: Jan 2002 Location: North American Continent	One big reason is that it does not work well with ungapped transformers because of the tendency to apply magnetic offset to the trasformer core. Since the half bridge drives the transformer through a capacitor, any DC component in the pwm waveform is blocked. __________________ USMPS http://groups.yahoo.com/group/switchmode/

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25th January 2004, 10:59 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	Push-pull also requires double the voltage ratings on the switch transistors. For off line 240V the high voltage FETs have too much loss due to RDS. IGBTs may be used with less loss, but they are not quite as fast.

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