Replace 10 PP3 batteries with 4 AAA batteries?

I have a piezo driver that consists of a 555 timer supplying a signal to a high power opamp. The setup works well, the piezo vibrates. The problem is that the opamp and piezo require around 80Vpp. So my portable device is using 10 PP3 batteries. I would like to replace the PP3 batteries with 4 AAA batteries.

These are my input and output power requirements. They aren't fixed in stone.

For opamp supply I require +40V to -40V. Opamp max output +35V to -35V at 50mA (About 4W)

4 AAA batteries supply 6V and 2A at a push. I say at a push because my piezo will only have a life of 5 minutes so I'm happy to burn out the batteries.

Piezo power +/-40V at 30mA

How should I do this?

Thanks.

You need a switch mode power supply, which will require a custom transformer.

But instead of that, why not just use a custom transformer to feed the piezo from a lower voltage amplifer (which is what's normally done).

I do have another piezo driver, it is a 555 timer - audio amp - transformer - piezo. It works ok. The problem with that setup is that it requires 8 PP3 to provide current to the amp, or alternatively the two 12V lead acid batteries I have. So it isn't any more portable. Maybe I need a different amp from the two I have? I don't know what is simplest.

You need to design the transformer and amplifier to work from a lower voltage, you can get 4W from a 12V supply to a 4 ohm load.

Hello people,

Can this schematics be used as step up converter ?

2-transistor Black Regulator

The audio amp I currently have (LM3886) has a minimum supply of +10 and -10V. As an audio amp it has an ideal output impedance around 4 ohms. So typically into the transformer I get 3Vrms at 1Amp and 3Watts. That is fine and the transformer does the rest.

I don't see how I can get 4 AAA batteries to do this, I also need a bipolar output. I must think/design.

antknee said:

The audio amp I currently have (LM3886) has a minimum supply of +10 and -10V. As an audio amp it has an ideal output impedance around 4 ohms. So typically into the transformer I get 3Vrms at 1Amp and 3Watts. That is fine and the transformer does the rest.

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A normal amplifier IC isn't a very good choice, they lose too much of the available power supply - best choice, as I said, is a 12V supply and a car radio IC which will give 4W to 4 ohms. Or a bridged IC, which will give 16W to 4 ohms.

How do you manage to only get 3V RMS off a 20V supply?, you're losing over half of the supply.

I don't see how I can get 4 AAA batteries to do this, I also need a bipolar output. I must think/design.

Click to expand...

Why would you need a bipolar output?.

Nigel Goodwin said:

A normal amplifier IC isn't a very good choice, they lose too much of the available power supply - best choice, as I said, is a 12V supply and a car radio IC which will give 4W to 4 ohms. Or a bridged IC, which will give 16W to 4 ohms.

How do you manage to only get 3V RMS off a 20V supply?, you're losing over half of the supply.

Why would you need a bipolar output?.

Click to expand...

I get it, I was just looking at high current opamps, I will have a look at car radio IC's. The additional problem I have is that I need a fair amount of bandwidth, 100KHz isn't too far away from audio but some chips run out of gas at 20KHz. I'm losing a fair amount of power from the LM3886, partly due to slew rate and partly due to heating, its got quite a big heatsink. I couldn't say exactly how SR and heating interact with regard to power. I really want to shrink everything down, to reduce the number and weight of batteries and not need the big heatsink and chip, it is a bit over powered at a max output of 68W for my more modest needs.

PZT expands with a positive voltage and contracts with a negative voltage so this is how it can be used in vibration mechanisms. They can be broken through cracking if they vibrate too much. For example a piezo might be fine at +/-40V but if operated at 0-80V it may break at 45V so you lose vibration from -40V to 0V but only gain 40-45V. That said the piezo i'm using might be ok for higher positive volts, I haven't tested it for that, but now I have realised I should.