# Removing +8v bias from pulsed DC

Discussion in 'General Electronics Chat' started by ceaman, Jul 3, 2009.

1. ### ceaman Thread Starter New Member

Jul 3, 2009
1
0
Please be kind, its my first post!

I am trying to remove an +8 volt bias from a pulsed DC signal. The signal has a peak pulse of 60 volts and ranges from 8 hz to 70hz. I need to bring the bias as close to 0 volts as possible, and have an output trigger of at least 5 volt. Power supply voltage is 12 to 15 volt.

I tried using resistors to lower the voltage but I compressed the pulse until it couldnt be detected.

I am thinking I need to build an op amp. Suggestions please!

Jeremy

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
294
Usually, you pass the signal through a capacitor to remove DC.

We could use a schematic - the mention of power supply voltage is hard to understand in the context of a 60 volt pulse and a 5 volt trigger.

3. ### SgtWookie Expert

Jul 17, 2007
22,201
1,806
Is it a square pulse, or a sinewave?

Apr 5, 2008
19,291
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5. ### SgtWookie Expert

Jul 17, 2007
22,201
1,806
If it's a pulse, you might use a circuit like the attached.

Click on the small picture to open it. You may have to click on the window that opens up to see it full sized.

It uses a capacitor (C1) to block the DC level. R1 limits the maximum current. D1 is a 5.1v 1W Zener diode that clamps the output to 5.1v; it also keeps the output from going very far below ground.

If the output goes to a microcontroller or other sensitive device, use an appropriate current limiting resistor between SigOut and the uC.

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6. ### russ_hensel Distinguished Member

Jan 11, 2009
825
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What do you mean by an 8 volt bias, the average is 8 volts, the low level sits 8 volts off 0, or the peaks are symetrical about 8 volts? The question about the wave form is also important. Is this a periodic wave or perhaps a pulse produced by a sensor and intermittent?

7. ### millwood Guest

it depends on what you mean by "bias". a pusled dc (0 - positive rail - 0 for example) by definition has dc content in it and the only way to get rid of it is to swing it from negative to positive.

if your "bias" is such that the pulsed dc swings from 8v - positive rail - 8v, that's easy to deal with: just put a comparator there that is triggered if the dc signal goes above 8v.

which solution is best depends on which problem you have.