0.3V Reference Component

Hi,

For a variable input voltages ranges from 0 V to 2 V, I want a component whose output voltage should not increase beyond 0.3V.

For example:
Input 0.05 V - Output 0.05 V
Input 1.5 V - Output 0.3 V

We can have voltage dropper before that component as like as in zener diodes.

Is there any component for this low reference of 0.3V?

What is the relationship between i/p and o/p for the volatge swing?

You gave the input 0 to 2v and o/p as 0.3v.
Is there a table that gives the relationship between i/p and o/p voltage for each increment of 0.1v or 0.5v in input?

Hi.

Maybe a schottky diode as (shunt) voltage limiter?

Klaus

Hi,

I've been thinking about this for a couple of days, and besides some sort of op amp circuit, which hasn't brought up any great ideas that I know...A resistor divider works out at a ratio of 0.172 (0.25V/1.45V), that could be 33k and 158k. Isn't a potential problem the 50mV low? If the supply is so stable that 50mV can be read with certainty, then maybe a simple resistor divider with higher wattage resistors could work.

References for MOS design notes I remember reading about were 0.6V and similar, and these were usually theoretical, not "off-the-shelf" parts. The other very low voltage references are only things I've seen inside ICs that require a ref, but are not ref. ICs.

I interpret the OP request differently. I think they want a circuit that is 'transparent' up to 0.3V then hard clips anything higher. Klaus suggests a Schottky diode clamp which might work but it depends on the current the reference has to supply and on how suddenly the clamp has to operate.

The only viable alternative I can think of is a comparator to sense the 0.3V threshold with a current feedback path to counteract any further rise in voltage. It would almost certainly require both positive and a negative supply to be able to clamp at such a low voltage.

Brian.

It would almost certainly require both positive and a negative supply to be able to clamp at such a low voltage.

Click to expand...

At least a positive supply of a few volts.

betwixt said:

The only viable alternative I can think of is a comparator to sense the 0.3V threshold with a current feedback path to counteract any further rise in voltage. It would almost certainly require both positive and a negative supply to be able to clamp at such a low voltage.

Brian.

Click to expand...

Can you please elaborate this further in detail.. How do i use comparator with current feedback?

I haven't got a specific design in mind but what I think you are asking for is a clamp to prevent a variable voltage rising above 0.3V.

The diode method is simplest but we really need to know more about the circuit conditions, are you drawing uA or Amps from the voltage? A diode works by passing current through it when Vf has been reached and that current stabilizes the voltage in conjunction with the source resistance. It works for low currents but because it wastes excess voltage it might also be electrically inefficient at high currents. It also has the drawback that the clamp isn't very precise, it starts to limit the voltage a little way before 0.3V and only fully clamps it when the diode junction is at saturation point.

A comparator allows you to compare all or a fraction of another voltage with 0.3V and gives a sudden on/off control at that voltage. In some circumstances that may be more useful to operate an active clamp circuit. At it's simplest, you wire the comparator so it operates a switch, below 0.3V the source is passed directly through the switch and at 0.3V and above, an alternative 0.3V source is provided instead.

Brian.

You didn't yet tell if you are imagining a "passive" circuit (like the zener diode example suggests) or if an additional power supply can be provided.

With an additional power supply, it's no problem to design an active circuit (using a voltage reference, OP amplifier and nonlinear elements like diode or transistor) with performs the intended operation. Speed of operation and expectable source and load currents have to be discussed.

For a circuit without additional power supply, there are only few (and inaccurate) options like the said schottky clamp.

FvM said:

With an additional power supply, it's no problem to design an active circuit (using a voltage reference, OP amplifier and nonlinear elements like diode or transistor) with performs the intended operation.

Click to expand...

Are you referring to a precision clamp, e.g. the one in the NatSemi AN-31 Op Amp Circuit Collection?

Maybe the person who posted the thread, BenzT, has a PCB constraint regarding space, as that hasn't been mentioned either.

A Germanium diode.

But it suffers the same drawbacks of a schotky. Perhaps worse.