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I want to create a signal to send through an electrode that my senior design group is designing. The signal is very well-defined because our electrode is going to be compatible with a very specific machine that serves as a waveform generator that we don't have access to. The electrode needs to deliver 800 mA regardless of the impedance of the system, which will be on the order of 220 Ohm, which will bring the voltage up to around 180 V. Unfortunately, our waveform generators only reach 10 V. Here is the description of waveform (bidirectional square wave):

enter image description here

Here are some of my ideas:

1) Transform a 120V sine wave from the wall to 180V. Then use an Op-amp to quantize it to a square wave. Then use a digital timer controlled switch to clip the duty cycle.

2) Create a bidirectional square wave on LabVIEW at the max voltage (10V), then use an analog boost converter to boost the signal to 180V. I understand that the boost converter is used for DC signals, so perhaps after stepping up the signal, we could send it through a capacitor and voltage divider to convert it to AC

I haven't taken any power electronics or digital logic classes, so let me know if I'm going about this the correct way. Also, I would love an exact solution instead a general one like "make a boost converter" because I don't know the details of devices like that :)

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  • \$\begingroup\$ Your sentence about converting to AC worries me. Either you phrased it bad, or you definitely should not be playing with 180Vpp. \$\endgroup\$ – Vladimir Cravero Mar 3 '17 at 21:00
  • \$\begingroup\$ Yeah I might have phrased it wrong because I don't really know what technically qualifies as AC. But yes, we do need that high of a voltage, and we'll make sure to get lots of supervision when running our tests. The application is neuromodulation, so the 800 mA is necessary and fixed \$\endgroup\$ – BaileyH Mar 3 '17 at 21:05
  • \$\begingroup\$ 1 : 20 step-up transformer 12 V : 240 V and you will need 20 x 0.8 A = 16 A at 12 V peak. The average current at 20 Hz is 16 A x 0.6 ms / 50 ms about 200 mA . Be careful about the leakage induction and high- frequency response of the transformer. Mind you, with that duty cycle you do not need that much metal in the core. \$\endgroup\$ – skvery Mar 3 '17 at 21:06
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    \$\begingroup\$ neuromodulation.. is that some kind of code for "Electric Chair"? \$\endgroup\$ – Trevor_G Mar 3 '17 at 21:09
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    \$\begingroup\$ @Trevor I think that's a closer match for neur al de modulation \$\endgroup\$ – Asmyldof Mar 3 '17 at 21:19
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schematic

simulate this circuit – Schematic created using CircuitLab

An idea of the circuit.

  1. use a separating transformer to boost the voltage.
  2. Use a MOSFET H-Bridge with appropriate HV gate drive circuit.
  3. Use a current feedback measurement to determine the load current
  4. USe a MCU that controls the bridge in PWM mode at high switching frequency, chopper like. It depends on the load type, how to maintain the current setpoint.
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