Small power DC voltage amplifier


Why such a name?

It is better admits under the name Voltage Regulator.

What is a voltage regulator?

nothing different than an amplifier with an DC voltage at the input with the function as command variable of the control circiut.

  • this amplifier must have a high bandwidth (yes, also when using for DC only) 

  • must have a high power supply rejection ratio and load rejection ratio

  • close relation power consumption/bandwidth depending from supply current

Comparison between discrete and integrated solution

Advantages and disadvandtages of an integrated single chip solution:

  • bad PSRR and LRR already starting at some kHz

  • some parts are very noisy

  • excellent low power consumption

  • in most cases good short circiut and over temperature characteristics

  • less board space

  • low cost

  • assembly costs for a few parts only

Advantages and disadvandtages of an discrete transistor solution:

  • enormous better PSRR and LRR when using a good circiut

  • in many cases a better noise

  • higher power consumption, depending on speed

  • short circiut and over temperature protection requires an additional circiutry

  • more board space

  • cheap, depending from transistors

  • assembly costs high

Why the whole expenditure? 

One can buy nevertheless finished voltage regulators, correctly - I do often exactly the same - for special applications however - clearly no, in addition I developed these circuits.


  • better rejection of interferences on the input

  • better load rejection at higher frequencies

  • good for sensitive circiuts. e.g. a power supply for operational amplifier, working under a high gain - or as power supply under a very bad input voltage.

  • easy expandable through passive parts

To the circuits

The circuits use favorable standard construction units, the circuits however not yet were optimized, neither on capacity or speed, it exist still plentifully action need. Nevertheless they already offer a superior power Supply Rejection Ratio, compared with integrated.


All circuits go out from the circuit in schematic 0, a circuit, which I needed once in such a way. The report shows, what developed from it. The input voltage amounts to 10.4 V, which an alternating voltage is superimposed.



Schematic 2 is already a good voltage regulator with good suppression of disturbances of the operating cutting. The breakdown diode of 6.2 V forms a reference tension of 6.9 V together with the lower basis emitter distance. The two transistors on the left half form a power source, which supplies the basis of the serial transistor with current.

Function: if the output voltage rises, then the lower transistor leads more to flow it from the power source more current rerouted into the lower transistor instead of into the basis of the serial transistor. The serial transistor closes increasingly. The output voltage drops again to the desired value. And in reverse.




Schematic 3 developed like schematic 2. The programming of the power source of the serial transistor takes place via an additional power source. Thus continues to rise in particular the power Supply Rejection Ratio still. On the load Rejection has this measure hardly an influence.



Schematic 4 is a shunt regulator. A parallel transistor to separate the load resistance. This increased or degrades the effective load resistance. The circuit needs a defined load resistance. It is fast, and has the best efficiency on full load conditions. By Rver always flows the same current.


Schematic 5 is a shunt regulator with a high open loop amplifier. This circiut is endangered for stability problems and needs a L-C combination at the ouput. Of course there are many other possibilities to make the circiut stable.


The used source, a DC voltage superimposed by a AC voltage

PSRR.jpg (79571 Byte)

Picture shows the power Supply Rejection Ratio of the circuits. Compared with standard voltage regulators the serious superiority of the schematics 3 and 5 for the LINE Rejection would have actually to be accepted by everyone without comment. Schematic 3 and 5 have high open loop into higher frequency ranges, from this exact compensating of the disturbance results. Without question these circuits are still easily in their efficiency optimize and improvementable.    

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