Novel Ideas Anyone? Goal: Switching between 2 Different Voltage Supply Sources

[blackshadow]

This is my goal:

1. Initially, my LOAD is supplied by a FIXED voltage source of >2.0V for load protection purposes.
2. Next, i have an independent voltage supply for which i want my load to follow its voltage level whenever i rotate its knob.

ANy bright idea?
Please share...

 

[Nigel Goodwin]

I suggest you explain more fully what you're trying to do, I can make no sense of it?.

 

[ericgibbs]

This is my goal:

1. Initially, my LOAD is supplied by a FIXED voltage source of >2.0V for load protection purposes.
2. Next, i have an independent voltage supply for which i want my load to follow its voltage level whenever i rotate its knob.

ANy bright idea?
Please share...

I thought we had solved that on your current thread.??
https://www.electro-tech-online.com/threads/pnp-mosfet-based-switch-what-went-wrong.119116/

 

[blackshadow]

I thought we had solved that on your current thread.??
https://www.electro-tech-online.com/threads/pnp-mosfet-based-switch-what-went-wrong.119116/

Yes Eric. We have successfully created a good design for this. However, i had another application goals and i needed a new conceptual design.


OK. i will explain it further:

I do have a load with several input DC supplies such as its POS supply, NEG supply and the VVA supply.
After supplying my POS and NEG supplies to the load, i woul like its VVA supply to be initially set at say 2.2V. This is to avoid initial power surge of my application if the VVA is randomly set to just any value.

Now, as i would like to change my VVA value (which is initially set to 2.2V), it must at least follow the input voltage coming from another variable power supply (my application needs 0 to 3.5V).

The challenge here is how will i interface the fix 2.2V initial value (it can get its source from the POS supply) to the other power supply such that when i start to rotate its knob to set my desired VVA value for the load, it will automatically transfer the operation from the 2.2V fix to this variable power supply.

 

[blackshadow]

I suggest you explain more fully what you're trying to do, I can make no sense of it?.

Hi Nigel,

thanks for your goodwill to look into my case.

OK. i will explain it further:

I do have a load with several input DC supplies such as its POS supply, NEG supply and the VVA supply.
After supplying my POS and NEG supplies to the load, i woul like its VVA supply to be initially set at say 2.2V. This is to avoid initial power surge of my application if the VVA is randomly set to just any value.

Now, as i would like to change my VVA value (which is initially set to 2.2V), it must at least follow the input voltage coming from another variable power supply (my application needs 0 to 3.5V).

The challenge here is how will i interface the fix 2.2V initial value (it can get its source from the POS supply) to the other power supply such that when i start to rotate its knob to set my desired VVA value for the load, it will automatically transfer the operation from the 2.2V fix to this variable power supply.

 

[KeepItSimpleStupid]

It can be done using an encoder for the knob, a digital potentiometer and setting (programming) the power UP wiper position. This would provide your reference.

 

[blackshadow]

Is there any other novel ideas in its simplest form?

 

[KeepItSimpleStupid]

It's not as bad as you think. This is essentially the app note https://www.electro-tech-online.com/custompdfs/2011/06/digpot7184.pdf but you can't use the digital pot specified.

I think you can use the MAX5128 (The interface is slightly different, unfortunately) **broken link removed** Looks like you would have to use the LS7183 https://www.electro-tech-online.com/custompdfs/2011/06/LS7183_LS7184.pdf quadrature encoder

If you use the evalualtion kit, you should be able to program the wiper. You just have to create a 3.5 V reference voltage for the digital pot and program the NVRAM. You'll have to buffer the divided reference too.

Here is a digital encoder. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ECW1J-B24-BC0024L-ND

You really havn't said what VVA is. The above would provide a buffered reference. I don't know if that's all you need (i.e. current requirements) If you had issues with ground loops, adding an AMP02 http://www.analog.com/en/specialty-amplifiers/instrumentation-amplifiers/amp02/products/product.html and a -5V supply would help that.

See, it's not that hard. Is it?