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high voltage amplifier with wide frequency range

schrieb im Newsbeitrag news: snipped-for-privacy@f24g2000prh.googlegroups.com...

Hello Steff,

Apex Microtech makes high voltage amplifiers.

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Distributor in Germany is Hy-Line.
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I think even the fastest of their amps is too slow for your application. Required slewrate:

150V*2*pi*4e6 = 3800V/us

Last but not least, if you have a cable at the amp-output, it will have at least 0.5pF/cm. The 2pF load you have in mind is nothing compared to the capacitance of a possible cable.

Best regards, Helmut from Germany

Reply to
Helmut Sennewald
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Hi,

I have to design a high voltage amplifier, that should amplifiy a 3Vpp sinussodial signal up to 300Vpp. Furthermore the amplifier should work with linear phase over the whole frequency range from 100kHz to 4 MHz. The load of the amplifier will be a capacitance from 2pF and a resistor with changing values higher than 100MOhm. The current, the amplifier should provide, is only up to 500mA. I need this amplifier for a measurement application.

I tried in the last days a cascode amplifier which was able to amplify the sinussodial up to 300Vpp. The great Problem is, that the sinus will be deformed. Additionally the phase isn't linear over the interesting frequency range. I also tried a complentary booster, but this couldn't provide the high voltage.

Is there anybody, who can help me?

Thanks for your help, Steff

Reply to
Adlerauge2001

On a sunny day (Wed, 14 May 2008 00:30:58 -0700 (PDT)) it happened snipped-for-privacy@web.de wrote in :

.5A @ 300V is a lot of watts, are you sure you mean 500 mA? Anyways you never get 500 mA in 2 pF with 100 MOhm @ 4 MHz and 300 V

I think Winfield has published some related designs here in the past, google?

Reply to
Jan Panteltje

Sorry, there was a mistake from me. The maximum current I expect is

50mA.
Reply to
Adlerauge2001

On a sunny day (Wed, 14 May 2008 03:07:12 -0700 (PDT)) it happened snipped-for-privacy@web.de wrote in :

Still have a problem, 300 V in 100 MOhm is 300 / 100000000 = 3 uA (micro Ampere). The impedance of a 2 pF cap at 4 MHz is 1 / j.w.C so about 1 / 6.28 x 2.10^-12 =

7961 MOhm, so insignificant current. ?
Reply to
Jan Panteltje

On a sunny day (Wed, 14 May 2008 03:07:12 -0700 (PDT)) it happened snipped-for-privacy@web.de wrote in :

Still have a problem, 300 V in 100 MOhm is 300 / 100000000 = 3 uA (micro Ampere). The impedance of a 2 pF cap at 4 MHz is 1 / j.w.C so about 1 / 6.28 x 2.10^-12 =

7961 MOhm, so insignificant current. ?

Correction, screwd up the math,

1 / 6.28 x 4.10^6 x 2.10^-12 = 19904 Ohm, 300V in 19904 Ohm = 15 mA.
Reply to
Jan Panteltje

Probably, but you need to be more specific.

First, are you looking for a consultant, or are you looking for technical advise from the group? For technical advise, I suggest you post a schematic somewhere, and perhaps an input/output waveform at a frequency where you're having trouble. For a consultant, say "who has time to work on this", and stand back for a deluge of mail.

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Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

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Reply to
Tim Wescott

Try your luck at Apex Microtechnology...

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D from BC British Columbia Canada

Reply to
D from BC

Sinusoids have only two parameters, amplitude and frequency. Sometimes it's easier to generate them than to amplify them. If your signal is a modulated sinusoid, you may find that you need bandwidth in excess of the carrier frequency.

Look into some of the techniques being proposed for cellular base station amplifiers to achieve high linearity with efficiencies higher than what's obtainable with Class A.

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Reply to
mike

"Helmut Sennewald" schrieb im Newsbeitrag news:g0fcik$t9l$01$ snipped-for-privacy@news.t-online.com...

Hello Steffen, just one more idea to reduce the high voltage requirement for the transistors. Try to use a good transformer. Therefore you should look in the RF-handbooks for wide bandwidth power amplifiers.

Best regards, Helmut

Reply to
Helmut Sennewald

What do you mean by "linear phase"? Are you specifying a maximum phase shift over your frequency range, or are you asking for a specific type of filter response and group delay response? If you want very little phase shift, you may be asking for considerable current drive. For a 5 degree phase shift, your amplifer effective output impedance needs to be between 1500 & 2000 ohms. That means you need to be able to drive betwwen 150-200 mA at 4 MHz. Maybe the 500 mA requirement wasn't as silly as first sounded. To be able to keep the amp from slew rate limitation, you need about 8-10 mA, but at that limit, your phase shift will be pretty bad. The 19Kohm reactance fo the 2pf at 4MHz means that a source impedance of 19K will cause a 45 degree phase shift, and a -3db drop in signal amplitude. Is that within you requirements? Since you are making measurements, you should tell us what the accuracy is in terms of amplitude, phase shift, and linearity. If the wave form you're measuring is sinusoidal, these are all you might need. For complex waveforms, more requirements would have to be specified (ie., group delay, overshoot, etc.).

-Paul

Reply to
Paul

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