0
\$\begingroup\$

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.

\$\endgroup\$
  • \$\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 '16 at 15:36
  • \$\begingroup\$ A circuit diagram of your existing push-pull driver would help us. \$\endgroup\$ – Steve G Jun 21 '16 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 '16 at 15:54
  • 1
    \$\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 '16 at 16:46
  • 1
    \$\begingroup\$ Is it really 2200 nF and not 2200 pF? So what is wrong about the previous answers? \$\endgroup\$ – Andy aka Jun 21 '16 at 16:46
1
\$\begingroup\$

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%.

\$\endgroup\$
  • 3
    \$\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 '16 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 '16 at 2:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.