dc-dc paralleling

[dark]

Hi, Can we parallel three LM2577 with low drop shottky diodes without problems. Rgds

 

[cowboybob]

First, a question for you:

Why do you want to do this? Are you looking for more current carrying capacity than what a single LM2577 can handle (per the datasheet)?

 

[dark]

First, a question for you:

Why do you want to do this? Are you looking for more current carrying capacity than what a single LM2577 can handle (per the datasheet)?

Yes .

 

[dr pepper]

I've wondered about this with 2576's, but instead of diodes on the o/p using 0/1r resistors to balance the current between them, just like multiple bipolar trannys on a power amp.
The devices have cycle by cycle current limit so you'd think each would only output its max, the thing is theres allways gonna be a difference in what each one thinks the o/p voltage should be, so current isnt allways gonna be equal.
If the load is allways more than one can provide then it might work, I dont know if one would get upset if the load was low and the other chip raised its o/p to higher than it wanted, maybe some mad oscillation that releases the magic smoke.
What do you want to power?

 

[cowboybob]

Since the LM2577 is supposed to have self-limiting current control, I can't think of a reason not to be able to parallel the outputs. Course, you'll have to make sure your input can easily supply the power you're looking for.

Now, to be on the safe (or conservative) side, you might want to put a hefty cap (electro, tantalum, maybe even a supercap [dpending on the output voltage]) on the output to "smooth out" current transitions.

That might also subdue, as Dr pepper resaonably suggests, any mad oscillations that rear their ugly heads...

Can't seem to find a PSpice SIM LM2577 to test the idea.

 

[dougy83]

Each boost converter already has a diode on the output, so there's no need to add another. Basically all three converters would share the output capacitor, as well as the feedback voltage. I can't see why there'd be any smoke being released due to oscillations.

I didn't see any overload shutdown mechanism, just the cycle-by-cycle current limit. This should mean that if any converter (having a higher reference voltage) lets the output droop sufficiently, another converter will take up some slack.

 

[dr pepper]

I think your gonna have to try it, if it works tell us.

 

[dark]

I think your gonna have to try it, if it works tell us.

Hi, If I try that I will surely let you know the results. Rgds

 

[simonbramble]

Short the 2 feedback pins together and the 2 compensation pins together and run them in antiphase then it should work. A better solution is this part:


https://cds.linear.com/docs/Datasheet/3787fc.pdf

 

[dr pepper]

Help me think on this one Simon, how would you configure them to run antiphase?

 

[simonbramble]

Ah... erm... good point. This chip is a bit too 'simple' then... I thought it had a sync pin on it, but on closer look they seem to have missed it off. You can't run it in antiphase

 

[dr pepper]

And I was hoping you could.