# Fast switching between two input powers

Hi

Anyone knows of an electric component that can switch between two input powers.

I have two DC input power,s one is 10V/2A and the second is 12V/2A . I want to be able to switch between the two without interrupting the function of my circuit . meaning without my circuit going off in between the switch.

output can be 6V/2A (I am Flex)

Just wanted to know what is the name of this electric component that can witch between the two without dropping power . I guess it is a fast switch with some kind of a capacitor . if you have a link to the actual component that would be very helpful .

Thank You

B

mfb
Mentor
Many transistors can switch in nanoseconds, with a reasonable capacitor the voltage doesn't fluctuate in any relevant way during that timescale.

If your output is at lower voltage, you need some electronics to get the voltage down anyway, I guess you can start there.

Hi mfb.

thank you for the quick reply !

i have been looking for a long time now , but still can't find one that takes two inputs . can you direct me to one that does on the http://www.mouser.com [Broken] ?

thank you

B

Last edited by a moderator:
NascentOxygen
Staff Emeritus
I have two DC input power,s one is 10V/2A and the second is 12V/2A .
[....]
output can be 6V/2A (I am Flex)
Hi benofer90. You have mentioned 3 voltage levels here, and also indicated a capacitor will smooth over the changeover. Then it seems there may be a moment where it's possible that one of your sources could find it is connected to a capacitor charged to a voltage exceeding that of the supply itself. To prevent damage, you'll need to make sure the supplies can tolerate this; otherwise, a diode may offer sufficient protection.

You are wanting to manually swap between supplies, but to incur no interruption when doing so? What circuit or device is your load?

anorlunda
Staff Emeritus
How about a make-before-break double pole relay. You can choose electromechanical or solid state.

Nidum
Hi benofer90. You have mentioned 3 voltage levels here, and also indicated a capacitor will smooth over the changeover. Then it seems there may be a moment where it's possible that one of your sources could find it is connected to a capacitor charged to a voltage exceeding that of the supply itself. To prevent damage, you'll need to make sure the supplies can tolerate this; otherwise, a diode may offer sufficient protection.

You are wanting to manually swap between supplies, but to incur no interruption when doing so? What circuit or device is your load?

i have two power sources:
1) 10V/2A battery
2) 12V/2A battery
3) LED

i want to connect the LED to a switch that is connected to the two power sources .
i will trigger the switch with a little signal(power) , so the switch default is the 10V/2A battery , once triggered it will switch to 12V/2A battery

NascentOxygen
Staff Emeritus
I want to connect the LED to a switch that is connected to the two power sources .
i will trigger the switch with a little signal(power) , so the switch default is the 10V/2A battery , once triggered it will switch to 12V/2A battery
Will the trigger signal remain present for all the time that the 12V is in use? What voltage is that trigger signal and what circuit does it originate from?

Will the trigger signal remain present for all the time that the 12V is in use? What voltage is that trigger signal and what circuit does it originate from?

Will the trigger signal remain present for all the time that the 12V is in use?
i can go either way . either keep the signal or not

What voltage is that trigger signal
i can work with any v up to 12v

and what circuit does it originate from?
manually activated . external circuit . meaning i will switch the signal from a separate power source .

berkeman
Mentor
i have two power sources:
1) 10V/2A battery
2) 12V/2A battery
3) LED

i want to connect the LED to a switch that is connected to the two power sources .
i will trigger the switch with a little signal(power) , so the switch default is the 10V/2A battery , once triggered it will switch to 12V/2A battery

NascentOxygen
Staff Emeritus
i want to connect the LED to a switch that is connected to the two power sources .
I'm wondering why you are fastidious about not interrupting the current to the LED even momentarily. I mean, is anyone going to notice? People will probably notice a slight step change in its brightness during the changeover, anyway?

Baluncore
2021 Award
Connect the 10V/2A supply to the load with a power diode. If voltage drop is a problem use a Schottky power diode.
Connect the 12V/2A with a physical on/off switch. For electronic control, replace the physical switch with a power MOSFET.
The diode will keep the 10V/2A supply connected while switching the 12V/2A supply.

berkeman
Connect the 10V/2A supply to the load with a power diode. If voltage drop is a problem use a Schottky power diode.
Connect the 12V/2A with a physical on/off switch. For electronic control, replace the physical switch with a power MOSFET.
The diode will keep the 10V/2A supply connected while switching the 12V/2A supply.

okay i made a little diagram . maybe this will clear things out ... ?
is there such a component?

That may be overkill. Here's one rated exactly 2 amps.

http://www.hascorelays.com/electromechanical-relays/cas-cs-series.html

Operating time is <= 7ms, Is that fast enough?

i think that would be fine ? I'm looking at the data sheet and can find instructions with respect to switching or connectivity

so if i want to drop the V like in this digram i will need one more component at the output of the first component ?

yes but can i get it in one component ?

berkeman
Mentor
When you diode OR, it is usually one diode per supplying rail, hence two diodes in your case.

When you diode OR, it is usually one diode per supplying rail, hence two diodes in your case.
any way i can find one component ? what should i be looking for in terms of google key words?

anyone can help ??

There is no one component that will do the job. You need to get one power diode and one switch.
If you do not understand switches, or how current only flows one way through a diode, then all the help you need is on the web.
https://en.wikipedia.org/wiki/Diode
https://en.wikipedia.org/wiki/Switch

Like that ?
and then i need to place a switch between the diodes and the load ?
the question which ground should i use , i know its intuitive to say any of them but i know there is some difference . ?

Baluncore
2021 Award
and then i need to place a switch between the diodes and the load ?
No, there is only one diode, the other is replaced with a switch.
Use circuit d.
There is only one earth and it is common to all. Join all the earth points together.
Keep the power diode on the 10V/2A supply. That is the lower voltage supply.
Replace the diode on the higher voltage 12V2A supply with a simple switch.

No, there is only one diode, the other is replaced with a switch.
Use circuit d.
There is only one earth and it is common to all. Join all the earth points together.
Keep the power diode on the 10V/2A supply. That is the lower voltage supply.
Replace the diode on the higher voltage 12V2A supply with a simple switch.

then i will have another issue. because the output won't be a constant v. i want it to be 6v
its two different inputs and one regulated output. granted i know i have to keep the inputs above a certain threshold depending on the component .

Baluncore
2021 Award
Then you need a voltage regulator to take the combined power.
Such as a; “DC 3~40V to DC 1.5~35V Voltage Step Down Transformer Module”. Set it to give 6V.
I have been using these converters from http://www.dx.com/
SKU 154907 cost is about US$3.00 They are DC switching converters which are more efficient than linear regulators so will give longer battery life. mfb Mentor What is the application? This starts to look like an x-y-question. What do you want to do with the LED, why do you have to switch between two different power supplies? Then you need a voltage regulator to take the combined power. Such as a; “DC 3~40V to DC 1.5~35V Voltage Step Down Transformer Module”. Set it to give 6V. I have been using these converters from http://www.dx.com/ SKU 154907 cost is about US$3.00
They are DC switching converters which are more efficient than linear regulators so will give longer battery life.

how do i connect all of them . two batteries , regulator , diodes ..?
do i connect before the buck or after the buck ?

Baluncore