Choosing the best clamping circuit and components.

[randrea]

Hello to everyone.

I have a Vx voltage on a resistor R = 50kohm ( 0 volts < Vx < 33 volts) .
This voltage is the input of a triggering high impedence circuit powered with 5V.
The voltage on the resistor must not exceed 5V for a protection reason.
The clamping circuit must not distort all the voltages on Rx lower than 5V.

The problem is that this voltage comes from an attenuation of a high voltage using high resistors.
When there are 5 V on R, i have a current of about 100uA.

What clamping circuit should I use?

Are 100uA sufficent to switch on a zener diode?
Can low leakage currents damage my high valued resistors?
Is it maybe better use a schottky diode in series with a 5V voltage?

Are there other better integrated clamping circuits?

Thanks to everyone who will make my knowledges growing up.

 

[FvM]

An important information would be required circuit bandwidth and acceptable error (e.g. caused by leakage current).

 

[randrea]

An important information would be required circuit bandwidth and acceptable error (e.g. caused by leakage current).

I have to detect 3.3V with a maximum error of 3% but i can regolate the trigger's thresholds.
the voltage is a dc voltage coming from a battery

 

[Vbase]

A schottky diode to 5V is the best method.

 

[asdf44]

Diode to 5V (schottky) or Diode to 3.3V (not schottky) is the most straightforward. Those requirements don't sound particularly exotic.

A 4.7V zener might also work (though the first one I pulled up had 2uA leakage at 2V, which isn't great for you).

As FvM brings up you'll also want to factor in parasitc C from your solution which will limit bandwidth and phase.

 

[Audioguru]

Are 100uA sufficent to switch on a zener diode?

You need to look at the datasheets for zener diodes. Some clamp their rated voltage only when they have a fairly high current but still conduct at lower voltages. Others are rated at a fairly low current. Temperature affects the voltage if the zener voltage is below 6V or above 6V.