As shown in the above, the output voltage of lm2576 is a stable adjustable voltage.
Fault phenomenon: voltage falls sharply after the connection to the load, and the motor can not run.
My testing work: (1) when the load is connected, I open. The input voltage is only 2.56 V, and output is 1.56 V, which is unable to drive the motor (normally input is 7.56 V and output is 5-12 V adjusted by potentiometer). The datasheet of LM2576 is here
http://www.hkinventory.com(2) after I replace the new battery, it is the same.
(3) I disconnect the load, the the 2576 works normally (input normally, and the output is adjustable)
(4) the resistance of motor is 0.8 ohm. unknown inductance is 2.7 ohm.
(5) the circuit diagram is incomplete because it is based on my drawing line followed circuit boards
(6) entity is a flow adjustable vacuum pump
