How is a "synchronous DC/DC" synchronous?

Go To Last Post
4 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi - so I understand what a synchronous DC/DC is. But - I just find it confusing to call it synchronous. So you have two PWMs that are almost inverses of each other... How is that synchronous?

Also, what is the opposite of a synchronous DC/DC? It seems to be non-synchronous but I've seen asynchronous used too.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I would consider non-synchronous and asynchronous to be synonyms in this context.

Synchronous, with respect to switch-mode supplies, means that they have exactly the same period. One, the master, actually triggers the slave. What will be different, between the two, is pulse width and pulse phase.

If the PWMs are generated from a common counter, as in an AVR, they are guaranteed to be synchronous.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

nleahcim wrote:
Hi - so I understand what a synchronous DC/DC is. But - I just find it confusing to call it synchronous. So you have two PWMs that are almost inverses of each other... How is that synchronous?

Also, what is the opposite of a synchronous DC/DC? It seems to be non-synchronous but I've seen asynchronous used too.

I think you either have "regular" switching supply that has a single FET and free-wheeling diode or "synchronous" switching supply that has another FET in place of the diode.

Replacing the free-wheeling diode with a FET means two things. Less power losses because FETs have smaller resistance and less voltage drop over them. But the catch is that you need to control the FET on/off yourself while diode just sits there. And that control signal is almost opposite the control signal of the actual switching FET, perhaps having some dead time between them or actively sensing the voltage so that both FETs do not conduct at the same time.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Theres two interpretations here: synchronous rectification as jepael describes and having a number of converters sychronised in terms of their clock. When you have multiple converters or a number of phases, you want to ensure they're not pulling current at the same time, otherwise you get a larger peak current demand. Thus you sync the converters so that whilst one is charging, the other is dumping. With muliphase converters, you want to ensure each phase is correctly times in order that the overlap is correct. Pc motherboards tend to use multiphase converters as you have a number of smaller inductors and capacitors for a given power output.