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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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FAN8902 Fiches technique(PDF) 9 Page - Fairchild Semiconductor |
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FAN8902 Fiches technique(HTML) 9 Page - Fairchild Semiconductor |
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9 / 14 page  FAN8902(KA3902) 9 In the steady state, the terminal voltage on a motor is consisted of a back EMF and the voltage drop on the armarture resistors. When the motor happens to be stalled, the back EMF becomes zero, and the motor current (IM) is quickly increased until a maximum values. Therefore the duty of the pin #12 output becomes lower because of the increase of the sense voltage (VRS). Also it makes the voltage (VLa) be lowered, then it makes the duty become lower again. This mechanism makes the motor current hold very low value in the stalled motor state. The voltage on pin #14 (VLa) ia calculated as follows: We can choose the ratio of the resistors, R2 and R3, as follows: - Applied the rated voltage on motor, and then measured the current IRAT - Matched the maximum command current, VCMD,MAX to IRAT. VCMD,MAX = VLa,MAX = RS × IRAT × 5 × 5 for example, if RS = 10mΩ and IRAT = 20[A] at VBAT = 13[V], VCMD,MAX = VLa,MAX = 10mΩ × 20 × 25 = 5V -VLa,MAX = 5V = VBAT × 1 × R3 / (R2 + R3) Ratio = R3 / (R2 + R3) = VCMD,MAX / VBAT = 5 / 13 Therefore, R2 : R3 = 8 : 5 The buffer OP-amp selects the lower command between VCMD and VLa so as to limit the stalled motor current to very low in the above figure. Because of much larger VLa than VCMD, the motor operating point stays at A. But the point gradually moves toward B’ and then B” through the curve from the instance of stall as the below figure. V La V BAT D × R3 R2 R3 + ---------------------- × = Assumed the saturation voltage of Q1 is zero. VLa curve × (1 / R) The voltage drop on the amarture resistance VLA VCMD IRAT VMOTOR,STALL VBAT VLA VLA VMOTOR Operating curve A B B’ B” |
Numéro de pièce similaire - FAN8902 |
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Description similaire - FAN8902 |
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