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# Choosing the best clamping circuit and components.

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#### randrea

##### Newbie level 2
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.

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

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

A schottky diode to 5V is the best method.

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.

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.

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