changeover switching types

[isurunalaka]

hi, i would like to know the difference between dead time switching and overlapping contact switching in manual changeover switches.

 

[KlausST]

Hi

A changeover switch has three connections. Let's name it A, B and COM.

A dead time switch:
* A - COM,
* Then none connected
* Then B - COM

A overlapping switch:
* A - COM
* A - COM - B (both A and B are conductive)
* B - COM

Klaus

 

[isurunalaka]

is not A - COM - B (both A and B are conductive) position unsafe?? because load is connected to both sources. what is use of this position?

 

[KlausST]

Hi,

is not A - COM - B (both A and B are conductive) position unsafe?? because load is connected to both sources. what is use of this position?

It depends on application.

Example: there are passive current transformers. They need a closed loop at it's outputs.
An open output generates very high output voltages that may destroy the tranformers. Or they can be dangerous.
So if you want to "disconnect" the load you have to short circuit the outputs.

There are semiconductor switches. Here the usual term is "break-before-make" and "make-before-break".
If you use a non overlapping switch in the feedback path of an opamp, then there is a big peak during switching, because the opamp output will go to saturation with an open feedback.

Klaus

 

[isurunalaka]

can you elaborate this with a utility power and generator power sources? i am still not clear on difference between dead time switching and overlapping contact switching in manual changeover switches.

 

[KlausST]

Hi,

can you elaborate this with a utility power and generator power sources? i am still not clear on difference between dead time switching and overlapping contact switching in manual changeover switches.

Please draw a schematic.

Klaus

 

[d123]

Hi, if this is like rotary switches that are mbb and bbm, I just understand (and checked with a voltmeter) that in a linear power supply using a make-before-break rotary switch with output voltages of 5, 7, 9, 12, 15V... for a split-second you get when switching from one position to the next 5 + 7, 7 +9, 9 + 12, 12 + 15V; in a break-before-make when switching/changing the switch position for a split second you'd get 5 then 0 then 7, 7 then 0 then 9, etc...
I read that mbb is useful for applications where the voltage spikes are not harmful to the circuit/device.