Buck Boost: no proper ground reference

Thread Starter

anhnha

Joined Apr 19, 2012
880
Here are two buck boost converter topologies with no proper ground reference.
Please explain what is the problem with it?


 
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Thread Starter

anhnha

Joined Apr 19, 2012
880
I think it is meant to say that there is no common ground between input and output. When switch is ON both input and output shares the common ground. However, as switch is OFF no common ground exists.
The author says that these topologies are unacceptable. That is what I am confused.
 

Jony130

Joined Feb 17, 2009
5,126
This circuit will work only if you have a floating input source. So, now instead of 3-terminal circuit, you have 4-terminal device.
 

Thread Starter

anhnha

Joined Apr 19, 2012
880
This circuit will work only if you have a floating input source. So, now instead of 3-terminal circuit, you have 4-terminal device.
Actually when analyzing the operation of these topologies I don't see any problem with them.
Could you give an example where it doesn't work?
 

Jony130

Joined Feb 17, 2009
5,126
Now we have a 4-terminal device instead of the usual 3-terminal, input source cannot have any low impedance connection between Vin and Vout.
Have you seen any single- supply circuit without common ground between Vin and Vout?
 

Thread Starter

anhnha

Joined Apr 19, 2012
880
Now we have a 4-terminal device instead of the usual 3-terminal, input source cannot have any low impedance connection between Vin and Vout.
Could you explain about low impedance connection? What is it?
Have you seen any single- supply circuit without common ground between Vin and Vout?
I don't remember but maybe those above are the first ones.
 

AnalogKid

Joined Aug 1, 2013
8,251
So what is the problem caused by no common ground? I see that there is no common ground in these topologies but don't understand why it is source of problems.
First, let's take a moment to savor the Buckeye's victory over Noter Doter...

OK, back to you... The *potential* problem exists only within the context of the application. If the overall system requires that the regulator input and output reference potentials be identical, that's a problem. If no such requirement exists, then no problem exists either. There is no such thing as one grand universal power supply circuit/system/solution. Supplies always exist in the context of their source and load. To proclaim that one supply technique is good and another is bad without any context or qualifiers is anti-instructional, arbitrary and sloppy.

And another thing - "proper" ground reference - ??? Let me counter that stupid proclamation with this: Whoever wrote that does not understand what a circuit ground is, "proper" or otherwise. Again, no context = no brains.

ak
 

Avid0g

Joined Apr 1, 2018
21
I just encountered this problem. I am attempting to purchase some buck-boost converter regulators in order to install a new device in my car. The car battery, loads, and new system should all have a common ground, or my device design will be excessively complicated. However, almost all the regulators on eBay happen to have the current sense resistor located between the two negative leads.

In the same sense, each example in your image has one component connected between the battery and load on the negative sides. That makes the converter unsuitable for many existing systems, and each converter example will fail in various ways if the battery and load are inadvertently connected together by their negative leads.
 

Avid0g

Joined Apr 1, 2018
21
My point was, if you are going to design a general purpose circuit for the market, it is best to avoid making it widely unsuitable.
 

AnalogKid

Joined Aug 1, 2013
8,251
it is best to avoid making it widely unsuitable.
"Widely" unsuitable and unsuitable for your application are not the same thing.

Also, this thread is not yours, and over two years old. Better to start your own thread and reference this one with a link.

ak
 
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