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Charge pump supply for opamp in radio

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Eugen_E

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max232 op amp power

Hello,

I need to make a radio(HF)<->PC interface powered on USB, and I use a double opamp, LM833, to make a differential amplifier. The opamp output goes to PC souncard - Line In, for signal processing.
Because the opamp needs positive and negative supply, and USB has only 5V, I thought I can use MAX232 or MAX202 circuit to generate ±10V.
I try to avoid using an low voltage, low noise, rail to rail opamp, because I cant find one localy. LM358 is quite noisy.

I want to ask if MAX232, MAX202 - being a switching source will interfere badly with the RF portion of the radio, or if it will generate parasitic signals at the opamp output.
I will use an RC filter on the opamp power lines (V+, V-), and the opamp PSRR is quite high (though it is measured at low frequencies).

So, if someone used MAX232/202 in a radio or high performance audio circuit, please share your opinion on this application.

Thanks
 

Eugen_E

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usb opamp negative

I want at least to know the switching frequency of MAX232 or MAX202 and what would be the "optimum" switching frequency range to minimize the interference on the radio.
 

IanP

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Using MAX232 as +/-voltage inverter is possible, but this circuit is very "noisy" ..
R-C filters may not be efficient enough, so consider L-C versions ..
Switching frequency is apprximately 200kHz, and MAX's internal charge pump conceptual digram is attached ..

Regards,
IanP
 

    Eugen_E

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