Need to Limit supply voltage in a certain range for the input of my circuit.

[AkshayaBhardwaj]

Need to Limit supply voltage in certain range for input of my circuit.

I have varying supply from 2.35 to 3.6 V.
On the basis of the signal X, I need it to be in the range of 1 to 1.8 V (when X=0) & 2 to 3 (when x=1)?
Any suggestion, how to do that?

Also transistors can have maximum of 2 V across their nodes.

 

[andre_luis]

Re: Need to Limit supply voltage in certain range for input of my circuit.

It seems like 'X' should be the output of the circtuit, not properly the input as you described above, otherwise 'X' itself could be used as the selector of an analog switch.

 

[AkshayaBhardwaj]

Re: Need to Limit supply voltage in certain range for input of my circuit.

Let me rephrase it different way. My input supply Vcc = 2.35 to 3 V. X is my selector through which I need Vout such that,

Vout = 1 to 1.8 V (When X=0)
Vout = 2 to 3 V (When X=1)

 

[d123]

Re: Need to Limit supply voltage in certain range for input of my circuit.

Hi,

Maybe you could adapt the UV/OV concept in this LT datasheet, using three resistors and two comparators/op amps as comparators to turn on (and off) two LDOs (with enable pins) configured to the voltages you require.

The formulas to calculate the resistor values are explained in detail in the datasheet.

Or, an inverter and a buffer/a buffer configured with two outputs, one inverting, to turn on (and off) two pass devices, biased to output the approx. required voltages, again, LDOs with enable pins are easier to implement. If it requires two variable output voltages in the ranges stated, I'm not sure how to implement that.

 

[d123]

Re: Need to Limit supply voltage in certain range for input of my circuit.

Hi again,

I don't think the schematic I posted is what you mean (2V across transistors)... If you need variable output, then maybe a MOSFET controlled as a resistor might work, I don't know, I've never used a MOSFET as a voltage controlled resistor.

Another suggestion is buck-boost, or two, which seems a poor solution for several obvious reasons.

If you only have 2V headroom, I recommend "low voltage circuit design" in a search engine, and you will find many ideas and schematics, papers, etc., besides books that resolve this issue with "turnkey" circuits, 90% using MOS devices. Medical electronic devices, e.g. hearing aids and pacemakers, seem to offer many low voltage solutions. The LMV951 is a 1V op amp that uses two switchers inside to create the headroom needed for the internal transistors to operate, a clever design.

 

[KlausST]

Re: Need to Limit supply voltage in certain range for input of my circuit.

Hi,

try this:



Klaus