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I'm looking for some kind of idea for controlled load for AC source testing. The output signal of source is a bipolar sine wave 5 Vpk (so it varies from -5V to 5V) and it has 1.5kOhm series resistance.

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My goal is to make a variable load, so the output voltage will be reduced to around 30% of nominal (unloaded) voltage value. That means that i need to figure out how to make a controlled resistance with values down to 750 Ohm. Or make some kind of variable load current source.

Reducing of signal should be smooth in all range or with possible small steps (not just on/off variable load) and sine can't be distorted. Microcontroller will be used for controlling.

The obvious solution is digital potentiometer, but these for bipolar signals (basically with ex. +-15V voltage supply) are not very common.

I will be grateful for any solution ideas for this problem. Thanks.

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    \$\begingroup\$ What frequency is the AC source producing and what range of load resistance values do you need? \$\endgroup\$ – Andy aka Mar 22 '15 at 16:32
  • \$\begingroup\$ its 1kHz sine wave. Resistance range is 5 kOhm down to 750 Ohm. \$\endgroup\$ – przeski Mar 22 '15 at 20:24
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A photoresistor or a thermoresistor with a heater may work for you. Or you can try R2R ladder with small relays; this way you can achieve up to 64 levels of resistance.

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