Help Needed! Rectifier Circuit

[Sajal Khokhar]

Hi, I am currently working on a passive rectifier circuit for an implantable device. I was wondering if anyone could tell me the equivalent impedence/resistance before the diodes in the circuit i.e. nodes x, y in the attached image. Is there an expression that can be stated for all rectifiers passive or active? How can this be calculated.

Thank you.

 

[AnalogKid]

Because a diode's voltage drop is relatively independent of the current through it, its effective impedance is a negative function of the current through it, and it is dependent on the circuit voltage. Because the signal is a sine wave, the instantaneous impedance of the diodes is changing constantly. Also, when the signal voltage drops below 1.5 V, the diodes stop conducting, basically jumping to an infinite impedance. So the circuit impedance is not a simple equation.

What is it you are trying to achieve with this information?
ak

 

[KeepItSimpleStupid]

It depends. See https://en.wikipedia.org/wiki/Diode_modelling for some modeling equations. rds is dependent on temperature and primarily dependent on current and what looks like to me the A-factor.

You should check into some of the ideal diode devices from linear Technology.

The OP is likely concerned about "power source" life.

 

[Sajal Khokhar]

The circuit above is an extension to an existing circuit. The estimated incoming voltage is 4.1V and frequency is 50kHz, so by trying to get the equivalent impedence/resistance I was hoping to check how the circuit effected the losses and also if it was in phase with the previous circuit

 

[tomizett]

You're probably best to do a numerical simulation with a tool such as SPICE. It will model the behavior of the diodes very accurately and allow you to plot a graph of the instantaneous impedance (from which you'll be able to work out the mean).

 

[Colin]

The diodes need to be "high-speed" for 50kHz.

 

[crutschow]

I would use Schottky diodes.
They work better at high frequencies and have a lower forward voltage drop than standard junction diodes.