Voltage Converter

[beakie]

Hi all

I am trying to build a board to go alongside my 13.8V (maplins, XM20W) bench power supply. I want to be able to switch between a 5V and 9V regulated power supply.

I also want to include a 7 segment display showing 5 or 9, depending on the current voltage selected.


Can anyone please confirm if they believe this will work/fail?

Will segment B be as bright as all the other lit segments when I am displaying a 9? I haven't decided on the resistors to be used yet, but this should only affect the brightness between 5 and 9 and not the seperate segments, right?



Any opinions/ideas/criticisms appreciated!

Thanks!!!

 

[Jon Wilder]

I would run the display off of the 13.8V supply. This way the brightness of the display won't change when changing voltage. There's no reason to run the display itself off of the switched voltage.

 

[beakie]

I would run the display off of the 13.8V supply. This way the brightness of the display won't change when changing voltage. There's no reason to run the display itself off of the switched voltage.

OK, good idea! Thanks.


The rest look about right? My diodes gonna work ok?

 

[beakie]

Amended:

 

[hdc090360]

Segment b will be brighter than the others because it doesn't have the voltage drop of the diode in series. Therefore the current will be higher. I would suggest you put a diode in series with it as well.

 

[beakie]

Segment b will be brighter than the others because it doesn't have the voltage drop of the diode in series. Therefore the current will be higher. I would suggest you put a diode in series with it as well.

I did wonder. OK, cool. Thanks a lot.

 

[Jon Wilder]

A much simpler way of doing this -

**broken link removed**

Only the output as well as the display need to be switch. There's absolutely no reason to break the supply circuit itself. For the record you can power that display off of any of the 3 available voltages in this version as well.

 

[beakie]

A much simpler way of doing this -

Only the output as well as the display need to be switch. There's absolutely no reason to break the supply circuit itself. For the record you can power that display off of any of the 3 available voltages in this version as well.

The display represents the voltage that is currently turned on. If there is 2 switches, then the value shown isn't neccessarily going to be the voltage currently turned on.


Edit:

I now realise this is a DPST switch and not 2 switches.

The only problem is, the 9V will still be active when the 5V supply is on.

 

[Jon Wilder]

The display represents the voltage that is currently turned on. If there is 2 switches, then the value shown isn't neccessarily going to be the voltage currently turned on.


Edit:

I now realise this is a DPST switch and not 2 switches.

The only problem is, the 9V will still be active when the 5V supply is on.

And why is that a "problem"? Are we only concerned with which voltage is appearing at the supply's output rather than which supplies are actually "on"?

And yes it's a DPDT switch...hence the "S1A" and "S1B" markings rather than drawing the dashed line between the two.

 

[beakie]

And why is that a "problem"? Are we only concerned with which voltage is appearing at the supply's output rather than which supplies are actually "on"?

I intend to have things connected to both 9V and 5V at the same time ...though with only one at a time having current.

Edit: Sorry, I get ya. Missed it. Cheeeeers

 

[Jon Wilder]

I intend to have things connected to both 9V and 5V at the same time ...though with only one at a time having current.

And what purpose would it serve to have things connected to the actual supply at all times if only one circuit was drawing current at a time?

On top of that, by feeding the 5V regulator off the 9V source, you'll reduce the heat dissipation of the 5V regulator compared to how much it would dissipate being fed from the 13.8V source.

 

[beakie]

One more question. In eagle, what is a basic DPDT switch called? Can't find anything non IC.

 

[beakie]

And what purpose would it serve to have things connected to the actual supply at all times if only one circuit was drawing current at a time?

On top of that, by feeding the 5V regulator off the 9V source, you'll reduce the heat dissipation of the 5V regulator compared to how much it would dissipate being fed from the 13.8V source.

It took me a few minutes but I realised that. Thanks for taking the time to look at this. You comments are greatly appreciated!

 

[Jon Wilder]

Glad I got the "wheels turning".

Not sure...I've just always used two SPDT switches and used the A/B labeling style.

 

[beakie]

Glad I got the "wheels turning".

Not sure...I've just always used two SPDT switches and used the A/B labeling style.

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