linear regulator with inverted output voltage?

[waveboy]

Dear Engineers,

Please may i confirm that a linear voltage regulator (as opposed to the switching type) cannot produce an output voltage that is an inverted form of the input voltage (i.e. a linear regulator cannot produce a negative output voltage if its input was a positive voltage).

Having said this, there are, i believe, methods of using additional circuitry with linear voltage regulators such that such voltage inversion can be realised. If any reader has a circuit diagram for such a circuit then i would be most grateful to be told of the relevant web page.

Best Regards.

 

[nbucska]

I know 3 possibilities ( never mind efficiency) :
1.) motor-generator
2.) heater--thermoelectric generator
3.) plasma generator -->magnetohydrodinamic generator

Inverting supply is possible only if it converts the electrical energy to some other kind like
Electrical --> mechanical -->electrical or
electrical --> thermal -->electrical or
electrical --> magnetic --> electrical

The last one is the switching regulator which doesn't
work with DC.



Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[LionelHutz]

No, a linear regulator can not invert the voltage. And no, you can't just add more resistors, capacitors or transistors to the circuit and make it inverting.

You need to add a switching circuit to do as you ask. In it's simplest form the circuit is like this;

oscillator -> switch -> inductor -> rectifier -> regulator

If you're switching you might as well use an inverting DC-DC converter circuit that produces a regulated inverted voltage.

 

[Comcokid]

There are linear regulators and LDO regulators for negative voltages, but you must feed them a negative voltage.

Negative voltages are generated from switching regulators and from inverting charge pump regulators.

Switching regulators use a switching voltage into an inductor to store energy that is then released and steered by a diode. You can buy ICs that have most of the functions on a chip - you only need an exteral inductor and fitercap, and sometimes a schottky diode or power MOSFET in addition to a few passive components. These types can be found from National, Linear Tech, Maxim, TI, Micrel, etc.

Charge-pump types use capacitors as the energy storage mechanism to increase or invert the voltage. You can buy these as ICs and generally need only two to four external capacitors. These types can be found at TI, Intersil, and others.

Waveboy, I assume this question comes from the post you made for the GaSFET transistor supply. In that one, It sounds like a 555 is used as a oscillator, then buffered to drive a diode/capacitor ladder to create both a higher positive and negative voltage. This is somewhat similar to the charge-pump type devices. Hex inverter ICs are also used in this manner with one inverter as the oscillator and the remaining 5 inverters paralled to buffer into a diode/cap multiplier arrangement.

 

[OperaHouse]

Always the contrarian, I've seen a three terminal regulator turned into a nifty 80 meter transmitter and it's not hard to make a 723 into a switching regulator. That said, I'm going on vacation and you will have to fend for yourself.

 

[VEBill]

Tesla was right, Edison was wrong. AC is often 'better than' DC. With almost every technique listed above, something is moving, turning, or oscillating.

The interesting exception is nbukska's #2 (heater - thermoelectric generator).

 

[jimkirk]

To add to nbucska's list, photo-electric. In fact I recall seeing a product from someone that included an LED and several photoelectric cells in series, all in a single IC package. Or you could roll your own. Select emitter wavelength to match the detector for best results, but still, "never mind efficiency".

Also as VE1BLL points out, the thermoelectric generator and photo-electric are DC, which may have an advantage regarding noise generation in some applications (low noise RF circuits for example). The AC solutions are generally much more efficient that the DC ones.

 

[Warpspeed]

A linear regulator can only regulate (or reduce)what is there. In other words the output voltage must be of the same polarity and always less, or closer to zero than the input voltage.

There are a great many schemes to increase voltage or reverse the polarity, but a linear regulator isn't one of them.