non-regulator_01 PUBLIC

A slightly edited version of arduinohacker's circuit. Added more net names and some analysis.

Assume the maximum drop of the schottky diodes is 0.5V. V(inn) can only be between 0V and 2 schottky drops (approx 1V max) above 0V. innp can only be between 0V and 3 schottky drops above 0V. The voltage drops across D8 and D2, D3, D6 are poorly defined because V(in) is set to 1V so has not fully forward biased any of the diodes. If V(inp) rises above 0V then OA1 will pull the base of Q1 up until it has pulled V(inn)=V(inp) through negative feedback. (An opamp with -ve feedback will try to make its inputs equal). However, D4 and D7 are not fully forward biased so will represent a fairly high resistance. Hence Q1 emitter will not have to supply much current hence the drop across R2 is likely to be small. Hence V(Plate_current) is likely to be not much higher than V(inp). Even quite high voltage at V(in) will only result in small voltages at V(inp) due to the small current flow through R1. If V(in) is raised to say 2kV then V(inp) becomes more well defined at about 1.5V. This drives OA1 input up and so OA1 drives it's output up. This turns on Q1 which tries to pull V(inn) up to equal V(inp). However, we have already said that V(inn) cannot exceed about 1V (there is insufficient drive available from Q1 emiiter and R2 to make the drop across R4 significant) so OA1 output drives hard high and shoves Q1 base up to the positive supply.

With V(in) = 1V as shown, it is not clear what this circuit is expected to achieve. Even with V(in) >> 1V it is still not clear what this circuit is expected to achieve.

Despite this, it is not clear why this circuit does not simulate in CircuitLab.

Reproducing this circuit in LTspiceIV shows the circuit behaviour as described. A zip of the circuit and the plot setup file can be found here:

https://docs.google.com/open?id=0B2wonnsWWfTXOTVmNDU2Y2MtYzJlZi00M2MyLWExZDAtM2JhY2NiNGI4ODBi