Can anyone tell me how it works?
In my opinion when U+ = U- the voltage Uo is constant no matter of the load resistor(R5). But this is only if U+=U-.
Electronic – Parallel Regulator
voltage-regulator
Related Solutions
note: question was originally about a current limiter
The LM317 with the single series resistor between output and adjust input is actually a fixed current source, not a current limiter. You don't need the LM317 to create a current limiter, a few discrete components will do:
For a limiting at 2mA you select a 330\$\Omega\$ resistor for \$R_{SENSE}\$. If there flows 2mA through it Q2 will start to conduct and reduce the base voltage of Q1, so that its current is cut off.
edit (re changed question)
Maybe you're focusing too much on the LM317. If you need a constant current you could use the LM234 which is a programmable current source for up to 10mA. You set the current with a resistor.
Fairchild datasheets for their LM78XX series of linear regulators contain a circuit for increasing the output using a resistor to hold the reference above ground. I guess how well it works in practice will depend on how stable the quiescent current is over the operating range for the AMS1117.
The above image was from the Fairchild 7805 datasheet that may be found here:
Related Topic
- Electronic – *very* Low voltage regulator
- Electronic – How does the power supply noise generated by digital ICs affect the output of regulator
- Electronic – FET-based voltage regulator with TL431
- Electronic – High Voltage Linear Regulator Output Not Staying Constant
- Electronic – Linear regulator that regulates even with negative current
- Electronic – Basic Op-AMP as voltage regulator
Best Answer
It's a shunt voltage regulator. The op-amp applies just enough gate drive to the MOSFET to keep both its inputs at the same voltage level and, in doing so regulates the voltage \$U_0\$ by shunting current through the MOSFET. Negative feedback occurs because of the inversion due to the MOSFET.
R5 is probably present to share the load thus taking some power dissipation away from the MOSFET. R5 also provides some loop stabilization in that the gain of the MOSFET is brought to less than unity and there should be little chance that the circuit turns into an oscillator although stranger things do happen.