For applications where good control of the speed of the motor is desired, but the precision of a tachometer control is not required, the circuit in Figure 8-11 provides control by using feedback of the current consumption to adjust the motor drive.

1. I_FLAG and T_FLAG connections are not shown.

2. Z₁, Z₂ = zener diodes (IN5246 or equivalent). Select Z₁ and Z₂ diodes that are capable of the maximum anticipated surge current.

3. S₁, S₂ = Schottky diodes (STPS1L40 or equivalent).

4. C₁ = high-frequency bypass capacitors; C₂ = low-frequency bypass capacitors (minimum of 10μF for every 1A peak current).

Figure 8-11 DC Motor-Speed Controller (Without Tachometer)

For more information on this circuit, see the DC Motor Speed Controller: Control a DC Motor without Tachometer Feedback the application bulletin, available for download at www.ti.com.