# positive to negative voltage regulator?

Discussion in 'General Electronics Chat' started by jut, Jun 14, 2009.

1. ### jut Thread Starter Senior Member

Aug 25, 2007
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2
Is there an IC that will take in a positive DC voltage and output a negative DC voltage?

Jul 17, 2007
22,183
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Aug 25, 2007
224
2
4. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
It's selectable x1 or x10 amplification.

The pot on the output gives you the capability to adjust the amplification to some arbitrary level between 0 and x10.

5. ### jut Thread Starter Senior Member

Aug 25, 2007
224
2
Ah, I see it now, thanks.

I'm trying to understand this circuit.

The "AC Coupling, 1M Impedance" section of the circuit is a high pass filter, right?

In the "150V input protection" part, what does the 47k resistor in parallel with the 100pF cap do?

6. ### SgtWookie Expert

Jul 17, 2007
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No, it's more of a bandpass filter. C1 blocks DC. R1 keeps the node floating around 0v. C2 acts as a short to ground for high frequency signals.

It limits current through D1/D2 if the input voltage exceeds the voltage rails.

7. ### jut Thread Starter Senior Member

Aug 25, 2007
224
2
Are you sure? I calculated the frequency response by hand and then using "ac analysis" in multisim; both gave the same result, a high pass filter.

Ok, makes sense.

I don't know what you mean by this.

Ok, makes sense.

I can see how the resistor limits current, but why put it in parallel with a cap?

Thanks for the help BTW.

8. ### SgtWookie Expert

Jul 17, 2007
22,183
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It'll look like that if you're only sweeping lower frequencies. If you go high enough in frequencies, C2 will start attenuating them.

re: keeps the node floating around 0v
OK. Run a transient analysis on it feeding the input a 1kHz square wave from 0v to 5v, for about 30mS. You'll see that the 1 MEG resistor pulls the signal down to average around 0v. Without that resistor, the average voltage level would float randomly.

Try doing an AC analysis on it.