A dropout issue with Mark III PSU design

[xReM1x]

hi, I have a problem where at voltage lower then 7V the regulator always must have 7V on the input, even if the output voltage is 10mV it still needs over 7V on the input, if the output voltage is higher then 7V then the dropout voltage is fine. (1-1.5V).
here is the schematic + download for ltspice *.asc:

[jitter]

Your question is not very clear. I'm assuming you mean that it won't simulate below 7 V input?

Well, a look at the datasheet of the real LT1074 might reveal why. It's generous that it lets you sim down to 7 V, if I were to use this step down regulator, then I would not dare go below the worst case spec of 8 V.

[Kleinstein]

The linear output stage might have a lower voltage limit due to R10. The base current of the power transistor might give quite some drop there at high currents. Though 7 V would be at high current.

[xReM1x]

The linear output stage might have a lower voltage limit due to R10. The base current of the power transistor might give quite some drop there at high currents. Though 7 V would be at high current.

problem fixed
I had to also change the positive voltage on the op amp to 30V and negative supply of 5V.
having problemos with the pre regulator doe

[mikerj]

having problemos with the pre regulator doe

Try using a buck

[xReM1x]

having problemos with the pre regulator doe

Try using a buck

this damn LT1074 what the heck it doesnt matter what resistor value I set R3 and R4 it will be always less then 1V! what.