Hello,

I was trying to develop this switch circuit in order to extract the maximum voltage from the piezoelectric element (that I have simulated as a voltage source in parallel with a capacitance) but I don't know how to set the parameters of the switch (it should close only at the maximum voltage output from the piezoelectric element). Can anyone help me?

 

Welcome to AAC!
You could replace V2 with a BV (behavioural voltage source) having parameters set to recognise the V1 waveform peaks, e.g. >19.9V OR <-19.9V. But why do you want to short the piezo with the switch?

 

Welcome to AAC!
You could replace V2 with a BV (behavioural voltage source) having parameters set to recognise the V1 waveform peaks, e.g. >19.9V OR <-19.9V. But why do you want to short the piezo with the switch?

I'm trying to simulate a piezoelectric material subjected to a sinusoidal force. The objective is to harvest as much energy as possible when the piecoelectric output voltage is at its maximum

 

I'm trying to simulate a piezoelectric material subjected to a sinusoidal force. The objective is to harvest as much energy as possible when the piecoelectric output voltage is at its maximum

What do you mean by "extract" or "harvest" energy? What do you want to do with it? Are you expecting to drive something directly (LEDs for example) or charge a capacitor, maybe trigger a transistor or TRIAC?

What you want the piezo to do will have a big impact on how you design your circuit.

 

What do you mean by "extract" or "harvest" energy? What do you want to do with it? Are you expecting to drive something directly (LEDs for example) or charge a capacitor, maybe trigger a transistor or TRIAC?

What you want the piezo to do will have a big impact on how you design your circuit.

The idea is to transfer the maximum output voltage from the piezoelectric to another element (for example a capacitor or an inductor) so I need the switch to turn on only when the piezoelectric material gives the maximum voltage

 

The idea is to transfer the maximum output voltage from the piezoelectric to another element (for example a capacitor or an inductor) so I need the switch to turn on only when the piezoelectric material gives the maximum voltage

It sounds to me a lot like a charge pump circuit, in which case you'd be fine conducting anytime the piezo voltage is higher than the target (cap, inductor, etc.) voltage. If that works, you could simply use diodes. You'd want to double check the maximum voltage ratings of the diodes and compare that to your piezo output. I don't remember for sure, but my gut feeling is piezo outputs can be really high voltage.

If you really wanted to eek out maximum efficiency, you might look into the technologies behind MOSFET-based active rectifiers. I don't know anything at all about them, except that I've seen them discussed here quite recently.

I could be wrong, but I suspect any mechanical switch/relay will be too slow for this application, plus the high voltages involved might cause unacceptable arcing (this whole paragraph is speculation - I'd need much more data than I have to say either of these things with certainty.)

Finally, if you really want a circuit that only switches at the peak voltage, then that would be a fascinating engineering challenge that's way beyond my skill level. I can imagine what I would do if I were coding a microprocessor for the task, but even if you wanted to go that route, you'd need a really fast ADC and microprocessor to get it done. The concept would be to measure the voltage as fast as you can, constantly calculating the rate of change. You'd set minimum thresholds for either voltage, rate of voltage increase, or both to recognize a positive pulse. Once you were in positive-pulse state, you'd monitor the rate of increase and wait for it to reach zero, and switch right then. I'm not sure how you'd know how long to close the switch (MOSFET?) for. I'm sure others here would know how to monitor rate of change in the analog domain, but I haven't a clue.

 

Energy harvesting at the peaks would waste most of the energy, and there's very little to start with .

 

Welcome to AAC!
You could replace V2 with a BV (behavioural voltage source) having parameters set to recognise the V1 waveform peaks, e.g. >19.9V OR <-19.9V. But why do you want to short the piezo with the switch?

How can I set the parameters of my BV? I'm trying with a if function but it doesn't work.

 

Here's one way :-