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I've been building an induction heater for a while now and wanted to get the frequency tracking to work properly. I need to convert the up to 600V ~100khz sine wave signal into a square wave, I've currently been doing it by using a 300kohm resistor and then clamping the voltage by using 2 back to back diodes.

The problem is that even very low capacitances of like those in a breadboard (~2pF) create a low pass filter which imposes a phase shift which makes tracking phase kind of hard.

How would I go about properly clipping the voltage without causing a phase shift?

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    \$\begingroup\$ How much delay (or phase shift) can you tolerate? Unless you have an amplifier that survives 600 volts (perhaps a vacuum tube's GRID) input), you will need a Voltage Divider. Two capacitors, one of 10pF and one of 590 pF, will produce 6.00 volts into a Schmidtt Trigger CMOS logic-interface IC, but that has 1nS to 20nS delay. Older technologies will be slower. What can you tolerate? \$\endgroup\$ – analogsystemsrf Jan 21 at 16:00
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    \$\begingroup\$ What do you mean by "tracking phase"? In the first part of your question you talk about "frequency tracking"? What exactly are you trying to accomplish? Is the frequency fixed or does it vary? Also, I don't think you should use a wireless breadboard at 600V. You should also be careful to use high-voltage resistors. \$\endgroup\$ – Elliot Alderson Jan 21 at 16:11
  • \$\begingroup\$ i also thought about a capacitive voltage divider, wont it be a low pass filter after all? Ill try it anyway, 20nS delay is more then acceptable, i can manually compensate and tune it aslong as it stays constant. \$\endgroup\$ – Eric B Ahapaid Jan 21 at 17:40
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As suggested in the comments, a capacative voltage divider was the way to go, althought I went for a simple 100pF capacitor to present a usable impedance to the signal diodes to keep the power loss low and then clamp the voltage using diodes.

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  • \$\begingroup\$ You can accept your own answer. This isn't a forum. If you don't accept your answer, then the question will keep floating around and showing as unresolved. As a new user, you might have to wait a day to accept an answer. \$\endgroup\$ – JRE Jan 22 at 10:26
  • \$\begingroup\$ I have to wait a day. \$\endgroup\$ – Eric B Ahapaid Jan 22 at 10:42

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