DC Motor Driver (Take class notes)Types of Driver1. Push-Pull amplifier2. Pulse-width modulation (PWM)3. Control of current• Push-pull amplifier (see circuit posted on the course website)- Assume current into the load is positive upper two transistors “on”; negative lower two “on”- Provides a voltage output at high current levels‐≅-Analysis-+=-Zero voltageMC 1533 operational amplifier=-Diode drop is not significantOutput currentβ1βββ [β1 β 15 20Ω I is provided to the motor; is from the amplifierPulse-width modulation (PWM)• PWM is the most popular deriver circuit• T = 50s equivalent to a 20 KHz switching rate which must be faster than the response speed of the motor so that the average voltage is seen by the motor• Advantages:- Full voltage across motor- Circuitry reasonable simple- On-off mode so that bias of the transistors is not critical, and transistors consume little energy 24 Typical PWM driver circuit – H bridge of Power EFT’s24 RFM 12P08 - P-channel FETRFM 12N08 - N-channel FETFor DN-or UP-when input Vgs< Vth→ onGateSourceDrainFor DN+or UP+when input Vgs> Vth→ onSensor resistorUse computer for PWM• Use 9 bits to modulate the pulse, and 1 bit for the sign (10 bits all together)• Resolution: 50s/512 0.1 s resolution for pulse width between 0 and 50 s• What is the function of the diodes in the PWM
View Full Document
Unlocking...