pwm 01
Description: A commercial motor controller is more than just a circuit designed to adjust the speed of a motor. It encompasses various features that enhance its functionality, which are explained in a guided overview. To effectively control the speed of a DC motor, a variable voltage DC power source is required. When power is applied to a 12V motor, it gradually accelerates; motors do not reach full speed instantaneously. If power is turned off before the motor achieves full speed, it will decelerate. By rapidly switching the power on and off, the motor can operate at a speed that is a fraction between zero and full speed. This principle is the basis of a Pulse Width Modulation (PWM) controller, which activates the motor in a series of pulses. The controller modulates the width of these pulses to adjust motor speed. For example, if the motor is connected to a battery with one terminal to the positive and the other to the negative through a switch (such as a MOSFET or power transistor), a short "on" period followed by a long "off" period results in slow motor rotation. A 50% "on" and "off" time leads to moderate speed, while a longer "on" time produces near maximum speed. In practical low-voltage controllers, the switching occurs at a frequency of 20 kHz, which is fast enough that the motor perceives a continuous DC voltage. This frequency is also above the audible range, minimizing noise. The switching frequency is manageable for MOSFETs. However, motors possess inductance, which resists changes in current. When the MOSFET is on, current flows from the battery through the motor and MOSFET, but when it turns off, the motor's inductance causes current to continue flowing. A second MOSFET, connected across the motor, allows for reverse current flow, functioning similarly to a diode. Alternatively, a power diode can be used. Notably, when MOSFETs are activated, they can conduct current in both directions, presenting lower voltage drops than forward-biased diodes, which reduces heat dissipation and energy loss. If the drive MOSFET operates at a 50% duty cycle, the motor voltage will be half of the battery voltage, and the average battery current will be half of the motor current due to the intermittent flow. However, when the MOSFET turns off, it disrupts both the motor current and the current from the battery, leading to potential issues due to the inductance of the battery wires.
The commercial motor controller is a sophisticated electronic device designed to manage the operation of DC motors through variable speed control. It utilizes a PWM technique, which allows for fine-tuned adjustments to motor speed by varying the duration of the voltage pulses supplied to the motor. The essential components of this controller include the power source, typically a battery; the motor; a switching device, such as a MOSFET; and the control circuitry that governs the PWM signal.
The PWM control signal modulates the duty cycle, which is the ratio of the "on" time to the total cycle time. For instance, at a 25% duty cycle, the MOSFET is activated for a quarter of the cycle duration, resulting in lower average voltage across the motor and thus reduced speed. Conversely, a 75% duty cycle allows for increased average voltage, leading to higher speeds. The rapid switching of the MOSFET at 20 kHz ensures that the motor operates smoothly without perceivable fluctuations, as the inertia of the motor allows it to maintain a consistent speed despite the pulsed input.
The inclusion of a second MOSFET or a power diode across the motor is crucial for managing back EMF generated by the motor when the MOSFET turns off. The inductive nature of the motor means that it will continue to generate current even after the switching device is deactivated. The second MOSFET or diode provides a path for this current, preventing voltage spikes that could damage the circuit components. This arrangement not only protects the controller but also enhances efficiency by allowing the energy stored in the motor's inductance to be recaptured.
The controller's design must also account for thermal management, as the MOSFETs can generate heat during operation. Proper heatsinking and thermal management strategies are essential to ensure reliable performance and longevity of the components. Additionally, the choice of MOSFETs with low on-resistance will minimize power losses and improve overall efficiency.
In summary, the commercial motor controller employs PWM to regulate motor speed effectively, utilizing MOSFETs for switching and managing inductive loads. Its design incorporates protective measures against voltage spikes and focuses on efficiency and thermal management, making it a vital component in various applications requiring precise motor control.A commercial motor controller is more than simply a circuit to alter the speed of the motor and we have a `guided tour` of controller features which explains simply most of the features incorporated into modern controllers and why they are needed. To control the speed of a d. c. motor we need a variable voltage d. c. power source. However if you take a 12v motor and switch on the power to it, the motor will start to speed up: motors do not respond immediately so it will take a small time to reach full speed. If we switch the power off sometime before the motor reaches full speed, then the motor will start to slow down.
If we switch the power on and off quickly enough, the motor will run at some speed part way between zero and full speed. This is exactly what a p. w. m. controller does: it switches the motor on in a series of pulses. To control the motor speed it varies (modulates) the width of the pulses - hence Pulse Width Modulation.
Consider the waveform above. If the motor is connected with one end to the battery positive and the other end to battery negative via a switch (MOSFET, power transistor or similar) then if the MOSFET is on for a short period and off for a long one, as in A above, the motor will only rotate slowly. At B the switch is on 50% and off 50%. At C the motor is on for most of the time and only off a short while, so the speed is near maximum. In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second).
This is far too fast for the poor old motor to even realise it is being switched on and off: it thinks it is being fed from a pure d. c. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency. However the motor has inductance. Inductance does not like changes in current. If the motor is drawing any current then this current flows through the switch MOSFET when it is on - but where will it flow when the MOSFET switches off Read on and find out!
Consider the circuit above: this shows the drive MOSFET and the motor. When the drive MOSFET conducts, current flows from battery positive, through the motor and MOSFET (arrow A) and back to battery negative. When the MOSFET switches off the motor current keeps flowing because of the motor`s inductance. There is a second MOSFET connected across the motor: MOSFETs act like diodes for reverse current, and this is reverse current through the MOSFET, so it conducts.
You can use a MOSFET like this (short its gate to its source) or you can use a power diode. However a not so commonly understood fact about MOSFETs is that, when they are turned on, they conduct current in either direction. A conducting MOSFET is resistive to current in either direction and a conducting power MOSFET actually drops less voltage than a forward biased diode so the MOSFET needs less heatsinking and wastes less battery power.
You should see from the above that, if the drive MOSFET is on for a 50% duty cycle, motor voltage is 50% of battery voltage and, because battery current only flows when the MOSFET is on, battery current is only flowing for 50% of the time so the average battery current is only 50% of the motor current! There is a problem however: when the MOSFET switches off, it not only interrupts the motor current but it also interrupts the current flowing from the battery.
The wires from the battery have inductance (so does the battery) so when this current is interrupted
The commercial motor controller is a sophisticated electronic device designed to manage the operation of DC motors through variable speed control. It utilizes a PWM technique, which allows for fine-tuned adjustments to motor speed by varying the duration of the voltage pulses supplied to the motor. The essential components of this controller include the power source, typically a battery; the motor; a switching device, such as a MOSFET; and the control circuitry that governs the PWM signal.
The PWM control signal modulates the duty cycle, which is the ratio of the "on" time to the total cycle time. For instance, at a 25% duty cycle, the MOSFET is activated for a quarter of the cycle duration, resulting in lower average voltage across the motor and thus reduced speed. Conversely, a 75% duty cycle allows for increased average voltage, leading to higher speeds. The rapid switching of the MOSFET at 20 kHz ensures that the motor operates smoothly without perceivable fluctuations, as the inertia of the motor allows it to maintain a consistent speed despite the pulsed input.
The inclusion of a second MOSFET or a power diode across the motor is crucial for managing back EMF generated by the motor when the MOSFET turns off. The inductive nature of the motor means that it will continue to generate current even after the switching device is deactivated. The second MOSFET or diode provides a path for this current, preventing voltage spikes that could damage the circuit components. This arrangement not only protects the controller but also enhances efficiency by allowing the energy stored in the motor's inductance to be recaptured.
The controller's design must also account for thermal management, as the MOSFETs can generate heat during operation. Proper heatsinking and thermal management strategies are essential to ensure reliable performance and longevity of the components. Additionally, the choice of MOSFETs with low on-resistance will minimize power losses and improve overall efficiency.
In summary, the commercial motor controller employs PWM to regulate motor speed effectively, utilizing MOSFETs for switching and managing inductive loads. Its design incorporates protective measures against voltage spikes and focuses on efficiency and thermal management, making it a vital component in various applications requiring precise motor control.A commercial motor controller is more than simply a circuit to alter the speed of the motor and we have a `guided tour` of controller features which explains simply most of the features incorporated into modern controllers and why they are needed. To control the speed of a d. c. motor we need a variable voltage d. c. power source. However if you take a 12v motor and switch on the power to it, the motor will start to speed up: motors do not respond immediately so it will take a small time to reach full speed. If we switch the power off sometime before the motor reaches full speed, then the motor will start to slow down.
If we switch the power on and off quickly enough, the motor will run at some speed part way between zero and full speed. This is exactly what a p. w. m. controller does: it switches the motor on in a series of pulses. To control the motor speed it varies (modulates) the width of the pulses - hence Pulse Width Modulation.
Consider the waveform above. If the motor is connected with one end to the battery positive and the other end to battery negative via a switch (MOSFET, power transistor or similar) then if the MOSFET is on for a short period and off for a long one, as in A above, the motor will only rotate slowly. At B the switch is on 50% and off 50%. At C the motor is on for most of the time and only off a short while, so the speed is near maximum. In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second).
This is far too fast for the poor old motor to even realise it is being switched on and off: it thinks it is being fed from a pure d. c. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency. However the motor has inductance. Inductance does not like changes in current. If the motor is drawing any current then this current flows through the switch MOSFET when it is on - but where will it flow when the MOSFET switches off Read on and find out!
Consider the circuit above: this shows the drive MOSFET and the motor. When the drive MOSFET conducts, current flows from battery positive, through the motor and MOSFET (arrow A) and back to battery negative. When the MOSFET switches off the motor current keeps flowing because of the motor`s inductance. There is a second MOSFET connected across the motor: MOSFETs act like diodes for reverse current, and this is reverse current through the MOSFET, so it conducts.
You can use a MOSFET like this (short its gate to its source) or you can use a power diode. However a not so commonly understood fact about MOSFETs is that, when they are turned on, they conduct current in either direction. A conducting MOSFET is resistive to current in either direction and a conducting power MOSFET actually drops less voltage than a forward biased diode so the MOSFET needs less heatsinking and wastes less battery power.
You should see from the above that, if the drive MOSFET is on for a 50% duty cycle, motor voltage is 50% of battery voltage and, because battery current only flows when the MOSFET is on, battery current is only flowing for 50% of the time so the average battery current is only 50% of the motor current! There is a problem however: when the MOSFET switches off, it not only interrupts the motor current but it also interrupts the current flowing from the battery.
The wires from the battery have inductance (so does the battery) so when this current is interrupted
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