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 Forum index » DIY Hardware and Software
a simple question about inversion and polarity.
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blinky_Palermo



Joined: Feb 07, 2014
Posts: 7
Location: taiwan

PostPosted: Sat Feb 08, 2014 12:07 am    Post subject: a simple question about inversion and polarity. Reply with quote  Mark this post and the followings unread

i'm working on a vactrol-based circuit running on a bipolar power supply.

the goal is to use an incoming signal to power two LEDs with inverse relationships to each other.

the incoming signal is full-wave rectified, so it is operating on a 0 to 12v range. if i invert that through an inverting op amp, i get a 0 to -12v range.

what i want is a 12v to 0v-going voltage, while the other voltage is going from
0v to 12v, if that makes sense.

any advice would be appreciated. thanks!
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analogmonster



Joined: May 30, 2011
Posts: 12
Location: Germany

PostPosted: Sat Feb 08, 2014 3:34 am    Post subject: Re: a simple question about inversion and polarity. Reply with quote  Mark this post and the followings unread

blinky_Palermo wrote:
i'm working on a vactrol-based circuit running on a bipolar power supply.

the goal is to use an incoming signal to power two LEDs with inverse relationships to each other.

the incoming signal is full-wave rectified, so it is operating on a 0 to 12v range. if i invert that through an inverting op amp, i get a 0 to -12v range.

what i want is a 12v to 0v-going voltage, while the other voltage is going from
0v to 12v, if that makes sense.

any advice would be appreciated. thanks!


Add +12 V to the output of your inverter stage you mentioned above?
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blinky_Palermo



Joined: Feb 07, 2014
Posts: 7
Location: taiwan

PostPosted: Sat Feb 08, 2014 5:19 am    Post subject: Reply with quote  Mark this post and the followings unread

well, that makes sense. i'm not sure why it evaded me. thanks!
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JingleJoe



Joined: Nov 10, 2011
Posts: 876
Location: Lancashire, England
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PostPosted: Sun Feb 09, 2014 12:29 am    Post subject: Reply with quote  Mark this post and the followings unread

in the past I've used a simple transistor inverter (google that) with a pnp transistor, 1 meg resistor on the base and 4k7 on the collector going to +V. you loose a bit of signal at one end (because of the forward voltage of the transistor) but it does the job if you don't need precision.
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