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As the "GSR" has featured peripherally in discussions in the "is this going 
to die" thread I decided to start a new thread related to it and others like 
it.

I'll make the following observation at the start. If people want to ask 
about it or comment on it please do so offlist to avoid annoying people who 
get annoyed by such things. While I am notionally the "inventor" of this 
circuit the design was actually proposed to me by God. Add a smiley to that 
if you want. The basic circuit fell fully formed into my mind essentially 
instantaneously immediately after I had provided a detailed written 
requirement. The design was to meet a very specific need, which it met and 
continues to meet very well indeed. This doesn't mean that it will meet all 
other needs as well, divinely inspired or not :-). GSR stands for 'God's 
Switching Regulator". End of discourse. Comments offlist please.

There are about 10,000 of these circuits in use at present. If it is used in 
a new project, which it probably will be, there will be 100,000+ of them in 
the next year or two.

The GSR is a buck regulator (maybe it should have been GBR :-) ) - so output 
voltage must be lower than input voltage (unless additional coils are added, 
which I have done).

It is usually not the most efficient circuit available.

It's attributes include
    Simplicity / low component count / low cost
    Tolerance to wide range of inductors.
    Good regulation for load and input variation, considering its 
simplicity.
    Operation over a VERY wide range of input voltages (20:1 in original)
    Extremely strange mode of operation (which probably helps reduce EMI 
substantially).

If you want a high performance circuit and cost is not important then you 
probably want to use one of the many many IC switching regulators available. 
If you want an ultra low cost design that performs surprisingly well then it 
may meet your need. As an amateur 9v battery to 5 volt converter it could do 
very well.

The "Black Regulator", refined by Roman Black from a circuit originally 
provided by Richard Prosser (if my memory serves) has less components and an 
even lower cost. It has worse regulation, requires larger inductors, tends 
not to like wide ranges of input voltages and it is much easier to 
understand its operation.

The attached GIF is subset from a larger circuit. It uses a high side P 
Channel FET as the main switch BUT most low power designs would use a small 
PNP transistor as the main high side buck regulator switch. In such cases 
zener ZBUK2 is not required. Resistors RBUK3 & RBUK4 would need to be chosen 
to suit the circumstances/

The original circuit had an output voltage of about 9 volts AFAIR and 
"switched" for input voltages from about 10 volts to 200 volts. The P 
Channel FET was rated at 200 volts and this set the upper (un)safe limit of 
operation. When Vin is below target output voltage the regulator acts as a 
pass through circuit with about 1v or less drop. This is important in the 
original application.

In operation the switching waveform of  the FET (or high side PNP or 
whatever) is "chaotic". No nice clean waveforms here. Switching can be made 
far more regular and efficiency improved by adding a series 
resistor-capacitor from the FET-Coil junction to the base of transistor 
QBUK2. You can expect that EMI levels may rise when you do this.

OPERATION:

It *probably* works like this ;-)

All off, Vout = 0, ZBUK1 doesn't conduct.
QBUK1 off so RBUK2 turns QBUK2 on which turns BUKFET on via RBUK3.
Voltage is applied to inductor via FET and current increases.
CBUK2 charges until ZBUK1 starts to conduct.
QBUK1 turns on (driven by ZBUK1) turning off QBUK2 turning off FET.

The following is standard buck regulator stuff:
Inductor 'rings" as current must continue to flow.
Right end of inductor now goes positive relative to left end.
DBUK2 conducts and CBUK2 voltage *RISES* as energy is transferred from 
inductor.
QBUK1 is held off as long as inductor has energy in it that drives output 
and can transfer energy to load fast enough to maintain ZBUK1 in 
conduction..
When inductor can't keep up the fight, CBUK2 falls *slightly*, ZBUK1 stops 
conducting and cycle repeats.

If there is an RC added as abovem, when inductor left end starts to fall, 
QBUK2 is driven off more quickly adding regenerative turn off. The reverse 
happens at turn on. This adds "formal" hysteresis and makes the circuit more 
understandable. There is in fact formal hysteresis present due to the eenrgy 
stored in the inductor, but some can't see this.

If the inductor is shorted out the design becomes a linear regulator. I have 
NEVER seen this circuit drop into a linear regulation mode but i have heard 
that reported by someone else who played with it.

Apart from the inductor there are a few tens of cents of parts used (if a 
small TO92 bipolar transistor is used instead of the FET. Inductor cost 
depends on application.





            Russell McMahon

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