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I have a 3.3v power supply (lithium ion battery) and am using a TI MPS430G2553 chip to generate a 25khz square wave using 2 PWM pins and a push-pull setup. This square wave goes from -3.3v to +3.3v. I need it to produce at least double that voltage (-6.6v to +6.6v) without messing up the 25khz square wave. I will be programatically changing the frequency of this wave from time to time, but will keep it within 1khz of 25khz.

The above circuit is driving a 25khz Piezo Transducer which has a capacitance of 2500pf. The current setup is producing about 80dB. I need 115dB. The datasheet on the Piezo says that at 10v (I'm assuming peak to peak), it will produce 115dB. So if I could double the voltage of the above circuit while maintaining the square wave, I believe I could accomplish my goal.

I have no additional power supply and would like to accomplish this with as few components as possible, for as low cost as possible.

Any recommendations with a circuit example would be GREATLY appreciated.

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  • \$\begingroup\$ An answer to your previous question suggested a transformer with a bridge-driver. You should probably research battery-powered, low-voltage bridges and signal transformers. \$\endgroup\$
    – user2943160
    Jun 21, 2016 at 15:36
  • \$\begingroup\$ A circuit diagram of your existing push-pull driver would help us. \$\endgroup\$
    – Steve G
    Jun 21, 2016 at 15:37
  • \$\begingroup\$ There's no circuit. I attach a the 2 terminals from my Piezo Transducer to 2 of the PWM pins on the MSP430G2553 chip. I should probably add a resister between the Piezo and the chip, but don't currently have one. Recommendations are welcome. I'm a software guy, not hardware. I can follow a schematic and assemble a circuit, but I am clueless as to its innerworkings. \$\endgroup\$
    – Curtis
    Jun 21, 2016 at 15:54
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    \$\begingroup\$ If you are just driving it directly from a MSP430, how are you currently getting it to go down to -3.3V? \$\endgroup\$
    – tcrosley
    Jun 21, 2016 at 16:46
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    \$\begingroup\$ Is it really 2200 nF and not 2200 pF? So what is wrong about the previous answers? \$\endgroup\$
    – Andy aka
    Jun 21, 2016 at 16:46

1 Answer 1

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You can run a 25KHz square wave through a 2:1 step-up transformer using a non-gapped core with little distortion if you are careful that the square wave has a duty cycle of exactly 50% and, if you use a push-pull winding on the primary, wind bifilar so that you have exactly the same number of turns. Any lack of symmetry will result in the having a DC bias and the output will be distorted. I often run a "D" flip flop divide-by-two on the driver circuit to make sure the waveform stays at 50%.

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    \$\begingroup\$ Without a dedicated driver, the transformer may result in excessive current draw between the I/O pins of the micro. There are convenient battery-spec dual half-bridges that could provide more drive, but still no amplitude calibration. The specifications of the transformer need a sufficient volt-time product to produce a square wave at 25kHz. \$\endgroup\$
    – user2943160
    Jun 21, 2016 at 19:13
  • \$\begingroup\$ I'm going to use a 3:1 step up transformer and perhaps a couple Transisters to give me some amplitude. \$\endgroup\$
    – Curtis
    Jul 1, 2016 at 2:24

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