# Full wave rectifier for piezoelectric stack

• lucy_b14
In summary, a capacitor may be needed to store the energy harvested from the impact, and the voltage and current required from the rectifier output must be known in order to choose the correct capacitor value.
lucy_b14
Hi

My project involves rectification of a voltage produced by a piezoelectric stack subjected to an impact. The voltage shall be rectified using a full wave bridge rectifier.

I aim to use a capacitor (in position of the smoothing capacitor) to store the energy harvested from the impact (simply because the device must fall from a certain height so it cannot be connected to any measuring equipment during its descent). The capacitor shall be disconnected following impact and connected to a volt meter so stored energy can be calculated.

My question is: does anyone have any suggestion as to how I can calculate required capacitor value? I have no idea of the frequency, current or voltage of the piezoelectric stack output, and these are likely to vary for different impacts.

I do know the voltage and current I require from the rectifier output - if that helps!

Any help would be greatly appreciated

Thanks

L

The biger the capacitor the more you can store.

capacitors are rated for voltage, so you'll need to know the maximum rectified voltage and maybe go a % higher for a safety margin. and you'll need to know the maximum energy output of the stack (or maximum signal applied if it's less than the stack capacity) to choose the total farads. you can use multiple caps in parallel if necessary.

edit: could it be that this is a system identification problem and that you'll have to do some lab work and analysis before you get down to designing the test instrument ? that's just the way it goes sometimes, you've got a black box and you've got to figure out how it works.

Last edited:
lucy_b14 said:
Hi

My project involves rectification of a voltage produced by a piezoelectric stack subjected to an impact. The voltage shall be rectified using a full wave bridge rectifier.

I aim to use a capacitor (in position of the smoothing capacitor) to store the energy harvested from the impact (simply because the device must fall from a certain height so it cannot be connected to any measuring equipment during its descent). The capacitor shall be disconnected following impact and connected to a volt meter so stored energy can be calculated.

My question is: does anyone have any suggestion as to how I can calculate required capacitor value? I have no idea of the frequency, current or voltage of the piezoelectric stack output, and these are likely to vary for different impacts.

I do know the voltage and current I require from the rectifier output - if that helps!

Any help would be greatly appreciated

Thanks

L

Don't use a full-wave rectifying bridge. That would be an error in either the project definition, or in your interpretation of the project definition.

Tell me why I make that statement. And tell me what kind of *single* diode you should use in this project, and why.

I'm afraid I can't work out what you're getting at. Having tested the piezo stack using an oscilloscope, it clearly shows an AC signal when an impact is applied. As far as I can tell, the only way to extract maximum available power is to rectify the output.

Please let me know if I'm getting confused here :)

Thanks

lucy_b14 said:
I'm afraid I can't work out what you're getting at. Having tested the piezo stack using an oscilloscope, it clearly shows an AC signal when an impact is applied. As far as I can tell, the only way to extract maximum available power is to rectify the output.

Please let me know if I'm getting confused here :)

Thanks

Well, if it's truly an AC output, with significant power in the negative excursions, then okay, a full-wave bridge might be justified. I'd assumed that the main power was in the initial compression of the piezo stack, which would put the main power in the initial voltage spike. Having just one Schottky diode drop versus two seemed like a good increase in efficiency, depending on the voltage levels you are getting from your stack.

it is certainly a valid question whether it's a true AC signal with a zero-volt average, or a DC signal with AC components (which would probably be a reflection of vibrations/bounce from the impact)

## 1. What is a full wave rectifier for piezoelectric stack?

A full wave rectifier for piezoelectric stack is an electronic circuit that converts alternating current (AC) from a piezoelectric stack into direct current (DC) by utilizing all parts of the AC signal. It is used to power devices that require a steady DC voltage, such as sensors or actuators.

## 2. How does a full wave rectifier for piezoelectric stack work?

A full wave rectifier for piezoelectric stack has four diodes that are arranged in a specific configuration. The AC signal from the piezoelectric stack is fed through the diodes, which only allow current to flow in one direction. This results in a DC signal that is smoother and more consistent than the original AC signal.

## 3. What are the advantages of using a full wave rectifier for piezoelectric stack?

The main advantage of using a full wave rectifier for piezoelectric stack is that it provides a more stable and consistent DC output. It also eliminates any negative cycles in the AC signal, resulting in a higher overall efficiency. Additionally, the use of diodes makes the circuit simpler and more cost-effective compared to other rectifier designs.

## 4. Are there any limitations to using a full wave rectifier for piezoelectric stack?

One limitation of using a full wave rectifier for piezoelectric stack is that it requires a minimum input voltage to function properly. If the AC signal from the piezoelectric stack is too low, the diodes may not conduct and the circuit will not work. Additionally, the circuit may produce some ripple in the DC output, which can affect the performance of certain devices.

## 5. How is a full wave rectifier for piezoelectric stack different from a half wave rectifier?

A half wave rectifier only utilizes half of the AC signal and results in a less smooth and consistent DC output compared to a full wave rectifier. This means that a full wave rectifier is more efficient and provides a higher quality DC signal. Additionally, a full wave rectifier can handle higher input voltages, making it more suitable for certain applications.

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