PWM Pre-Driver Feedback Control for HDD Fly-Height Heating
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Solution Overview
Problem
Hard disk drives (HDDs) face challenges in maintaining the optimal flying height of the magnetic head over the disk to prevent contact, which is difficult to control using existing temperature adjustment methods.
Innovation Solution
A system that generates a pulse-width modulated (PWM) signal to adjust the temperature of the fly element in the HDD, using a pre-driver with a modulator and a low pass filter to control the frequency and pulse-width of the signal, ensuring precise temperature control through a bulk-driven operational transconductance amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a coil is employed in the fly element to generate heat by iron loss or copper loss, then the temperature of the fly element can be adjusted to prevent contact with the magnetic disk, but the control precision of the temperature adjustment is insufficient
Solution Approach 1:
The patent employs pulse-width modulation (PWM) to apply periodic pulsed currents to the coil in the fly element. By varying the duty cycle of these periodic pulses rather than using continuous current, the system achieves precise control over the average heating power, thereby precisely controlling the temperature of the fly element to maintain optimal flying height.
2Temperature
If existing temperature adjustment methods are used, then the fly element temperature can be modified, but the flying height control is difficult to maintain optimally
Solution Approach 1:
The patent implements a feedback control system that monitors the flying height or related parameters and adjusts the PWM duty cycle accordingly. This closed-loop feedback mechanism ensures that the fly element temperature is continuously adjusted to maintain the optimal flying height, resolving the difficulty of maintaining precise height control with existing methods.
3Measurement precision
If a PWM signal is generated to adjust the fly element temperature, then the temperature control precision is improved, but the system complexity increases due to the pre-driver and low pass filter components
Solution Approach 1:
The patent introduces a low pass filter as an intermediary component between the PWM signal generator and the coil. This filter converts the pulsed PWM signal into a smoothed current signal that more effectively controls the coil heating while reducing electromagnetic interference and electrical stress on the drive circuitry, thereby achieving precise temperature control with manageable system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively maintains the flying height of the magnetic head, preventing contact with the disk by accurately controlling the temperature of the fly element, thus enhancing HDD performance and reliability.
Implementation Method 1
A coil can be employed in the fly element to generate heat by iron loss or copper loss. For example, when a current is applied to the coil, the fly element heats up and expands.
Data Source
AI summary
Systems and methods are disclosed that can be used to control an output signal, such as for controlling a heater for a hard disk drive. A system can include a pre-driver configured to provide a pulse-width modulated (PWM) signal to an output system in response to a control signal and a feedback signal, the output system being configured to provide an output signal for driving a load, the pre-driver comprising a modulator that provides the PWM signal in response to the control signal and a filtered feedback signal. A low pass filter is configured to receive a feedback signal with a voltage corresponding to a voltage of the output signal, wherein the low pass filter provides the filtered feedback signal that controls a frequency of the PWM signal to the modulator, the low pass filter having a bulk driven operational transconductance amplifier.