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1 kHz Modulation of a 50 kV power supply

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Erlend^SE

Mon Aug 01 2016, 04:10PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

You can't remove the switching frequency with feedback, it's a fundamental part of how the circuit works.
Still, you may get better bandwidth by tuning the feedback circuit, or make the circuit unstable and possibly self-destruct.

But you can change over some components to raise the frequency.
(that's why I asked about the controller, that seems to be a TL494 clone)

Whatever filters you add would have to be on the HV output, where all parts should ideally withstand at least 50 kV.
Input is likely good (you can meassure on the controller)

By having higher switching frequency, and some more output capacitance, you would get lower the switching noise on the output.
Capacitance lowers bandwidth, so you would have to do a trade-off.

I would suggest exploring the controller datasheet and TL494 datasheets before doing changes.
It's a key part of how it all works, and should not be ignored!

Physikfan

Mon Aug 01 2016, 09:02PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Erlend^SE

Unfortunately this generator is a commercial product and I have no electrical diagram.
Therefore I should build up a generator out my own ideas so I could control more of the really important parameters such as switching frequency etc.

Many thanks for your hints
.
My next step will be to raise the supply voltage up to 24 V and still using the load at the high voltage output.
50 kV would be to much for my P6015A but with the load the high voltage would be within the limit of 40 kV.

At least the signal of the switching frequency in the HV output is not really a great disadvantage.
Because I need this AC modulated HV power supply at the moment
only for testing the AC properties of some of my self built HV probes extending the range of 40 kV up to 80 or 100 kV.

Regards

Physikfan

Patrick

Tue Aug 02 2016, 08:53AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Are you trying to make a CW voltage adder ? i think you said that earlier ?

Erlend^SE

Tue Aug 02 2016, 12:02PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Physikfan wrote ...

Hi Erlend^SE

Unfortunately this generator is a commercial product and I have no electrical diagram.
Therefore I should build up a generator out my own ideas so I could control more of the really important parameters such as switching frequency etc.

Man

The datasheet for the controller actually kinda tells me how the whole circuit works.

TL494 datasheet, pag 13
This should give you a good start, if you want to figure out how the board works. It can't be very far from that.
(different topology, and different current feedback only)

I am currently doing my own high voltage supply.

Physikfan

Tue Aug 02 2016, 03:02PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Patrick and Erlend^SE

My plans are now to extend the voltage range of TEK 6015 up to 80 kV or 100 kV to be able to measure the output voltages of IGBT driven induction coils.

Also as a part of my job I have to build up Cockcroft-Walton circuits as well as Marx generators for physics demonstration experiments.
So I really need HV voltage probes with AC features up to 100 kV ore even more.

To accomplish this I have to check the AC properties of these extended HV probe versions.

My first experiment should be to use a P6015A parallel to a second 6015 in series with another 100 MOhm resistor and to compare the curvature of the two signals.

Regards

Physikfan

Patrick

Tue Aug 02 2016, 05:28PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Physikfan wrote ...

My first experiment should be to use a P6015A parallel to a second 6015 in series with another 100 MOhm resistor and to compare the curvature of the two signals.

i think this will be a disaster. i think youll just need a resistor ladder that goes up from ground to your highest capacitor. other wise this is going to lead to expensive long and bogus signal response.

the orange part is the 0-scope, you just keep adding stages to get to your voltage. then choose resistor values high enough as to not drag down your desired output current.

Erlend^SE

Tue Aug 02 2016, 08:39PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Remember a matching capacitor circuit for the measurement, or the bandwidth won't be very high.

resitive divider + capacitive divider.

Your Tektronix probe use capacitive divider.
Since it's very low capacitance, you may fail to recognise the parts of it, unless you look for it.

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