Does a push pull converter need an output inductor

[neonwarrior]

Hello everyone,
Does a push pull converter need an output inductor??
This schematics have no output inductor...



What is the output delta I (ripple current ) when there is no output inductor??
Thanks

 

[FlapJack]

The best answer is, it is supposed to have one. You will get something out without one so it will "work". But the inductor helps with regulating the output and stopping the primary from having to supply huge slugs of current with every load change.

 

[Warpspeed]

Hello everyone,
Does a push pull converter need an output inductor??

Yes it does, that circuit cannot possibly work properly otherwise.

Think about it.
If the duty cycle is varied by tweaking the "voltage adjust" potentiometer, the PWM duty cycle will certainly change up and down, but the PEAK voltage stays exactly the same.
As the capacitors will try to charge to the peak voltage, that is all you are usually going to get.

The peak ripple current with no choke will only be limited by the total dc resistance of mosfets and transformer windings.

Potentially destructively high.

The peak current spikes will be huge when the mosfets turn on, and nothing good will be accomplished.

A sufficiently large choke not only limits the current peaks, it averages the PWM output over the PWM cycle, so that the output voltage becomes controllable.

 

[Easy peasy]

Old Warp above is not quite correct, for a given load and given PWM, there will be an o/p voltage, even without an inductor, sure there are leading edge current spikes on the mosfets but the leakage inductance to the Tx takes care of the worst of it. there are literally thousands of psu's out there like this, a bit crappy but they work.

For e.g. for a 1k load and a PWM of 0.5% the o/p volts will be much lower than full available, volt reg is possible, ideally have balanced resistive loading.

 

[Warpspeed]

I suppose a crappy design deserves a crappy leaky transformer, so Easy P. has a point.

But if the impedances are low enough, the current spikes could be horrendous.

 

[treez]

yes I worked in one place where they were doing a bidirectional "Dual Active Bridge" converter.....its bidirectional. It operates like a "phase shift full bridge" SMPS but without the output inductor.....just uses the leakage........they thought it was the bees knees because it was bidirectional.....I thought it was awful I must admit. This current "fashion" to have bidirectionality in an SMPS no matter how poor it makes it , and no matter how needless and overcomplicated it is.

 

[FlapJack]

I suppose a crappy design deserves a crappy leaky transformer, so Easy P. has a point.

That's funny.