DC motor drive circuit

Circuit working principle: The feedback signal is sampled from the 3W current sampling resistor R. The two ends of
are connected to the two inputs of the op amp, and the signal is forced to flow through R. The current remains
unchanged. The calculation formula of the output current is as follows:
  Iout=(Vin/Rsc) (R2/R1)
  Select R2=R4=lk Ω, R1=R3 =100 k Ω, Rsc=0.25 Ω. In this way,
when the input voltage is 6.25 V, an output current of 2.5 A can be given. R1 to R4
use resistors with an error of 1% and 0.25 W, and the operational amplifier should be fixed on the heat sink.