Designing a power supply that works both in continuous and discinuous conduction!!

Thread Starter

supermankid

Joined May 26, 2013
54
Hi all,

I want to design a power supply for FPGA, where the core current can vary from few milliamps in sleep mode to about 16 Amps at maximum core usage. I have investigated a lot of switching regulators. Is there any pit fall that should be considered while designing the power supply which runs in both light load and very high load. Do the regulator in market can handle these cases easily or do I have to consider other special techniques??

Thanks for sharing your knowledge.

Nice weekends everyone!!
 

Thread Starter

supermankid

Joined May 26, 2013
54
Mr Chips, I was talking about inductor current ripple. #12s stuff is pretty not related to my question(though useful info). I hope you understand my question.
 

MrChips

Joined Oct 2, 2009
24,401
Sorry, then I don't understand the question.

If you need a power supply to deliver 16A @ 5V then that is what you need.
 

paulktreg

Joined Jun 2, 2008
803
I'm with MrChips. You need a power supply capable of 5V @ 16A. If your load only requires a few mA then that's all that it will supply.
 

crutschow

Joined Mar 14, 2008
27,895
Some control chips are designed to handle small loads in discontinuous mode, which would be stated in the data sheet or description of the chip. I don't know off-hand which those are so you'll have to search. TI and Linear Technology are two good places to start. Discontinuous mode can cause more ripple in the output voltage if the circuit isn't designed for that.
 

t06afre

Joined May 11, 2009
5,934
You can add a resistor as fixed load. To ensure that the current draw never drop below a point there the regulator will "fail" perhaps combined with some indicator LEDs on your board. You should always find the minimum current draw in the power supply datasheet
 

Thread Starter

supermankid

Joined May 26, 2013
54
Some control chips are designed to handle small loads in discontinuous mode, which would be stated in the data sheet or description of the chip. I don't know off-hand which those are so you'll have to search. TI and Linear Technology are two good places to start. Discontinuous mode can cause more ripple in the output voltage if the circuit isn't designed for that.
Thanks Mr. Crutschow. This was what I was talking about. Is there a some kind of trick to minimize ripple output voltage. If I have enough phase margin of y power supply, can I assure that it will work fine in both continuous and discontinuous mode?
 

crutschow

Joined Mar 14, 2008
27,895
I think for best operation in discontinuous mode you need a controller specifically designed to handle that mode. Don't know of any other tricks to minimize output ripple except to increase the output inductor and/or capacitor value. But it should still be stable if you have sufficient phase margin, although the output pulse rate may become somewhat erratic. Note that the ripple in the discontinuous mode may still be entirely acceptable for your application requirements.
 

Thread Starter

supermankid

Joined May 26, 2013
54
I think for best operation in discontinuous mode you need a controller specifically designed to handle that mode. Don't know of any other tricks to minimize output ripple except to increase the output inductor and/or capacitor value. But it should still be stable if you have sufficient phase margin, although the output pulse rate may become somewhat erratic. Note that the ripple in the discontinuous mode may still be entirely acceptable for your application requirements.
Thanks a lot. I needed some direction to start my investigation. You are the man of the day :)
 

t06afre

Joined May 11, 2009
5,934
Sorry, then I don't understand the question.

If you need a power supply to deliver 16A @ 5V then that is what you need.
Then some power supplies are not loaded with a specified minimum load. They voltage may go outside the setpoint. A quite common problem for a designer to take into consideration
 

inwo

Joined Nov 7, 2013
2,419
Seems a tiny linear supply for sleep mode would make sense.

That's what tvs do. Starting the main supply on wake-up.
 

THE_RB

Joined Feb 11, 2008
5,438
What FPGA draws 16 amps?? :eek:

Is that some kind of instantaneous peak current? That's what decoupling caps are for.

And if the average current is indeed 16A, then what is the peak current?

You really need to supply better info if you want help with the PSU design. :)
 
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