Card Reader Chopping Drive Circuit for Waveform Accuracy
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Solution Overview
Problem
Existing card readers face challenges in recording magnetic data with a favorable reproduced waveform using chopping current, as fluctuations in the chopping current lead to poor waveform reproduction, and the use of resistors increases circuit size, cost, and heat generation.
Innovation Solution
A card reader with a writing coil and a chopping circuit that supplies a chopping current with a controlled on/off cycle and duty ratio, allowing for adjustable magnetization strength without the need for resistors or multiple power supplies, simplifying the circuit and reducing heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor is used to limit the write current, then the current can be controlled, but the resistor mounting area increases, causing enlargement and increased cost of the drive circuit
Solution Approach 1:
The patent extracts the current limiting function from the traditional resistor-based approach and implements it through a chopping circuit that uses pulse-width modulation. The chopping circuit generates a chopped write current with controlled duty ratio to achieve the desired effective current value without requiring large-power resistors, thereby reducing the resistor mounting area and overall circuit size.
Solution Approach 2:
The patent applies periodic chopping action to the write current, turning it on and off at a high frequency with a controlled duty ratio. This periodic modulation allows the effective current value to be reduced while maintaining the ability to control magnetization strength, eliminating the need for large resistors that would be required for continuous current limiting.
2Reliability
If a resistor with large allowable current is used, then the current limiting function is achieved, but heat generation from the resistor increases
Solution Approach 1:
The chopping circuit applies periodic on/off switching to the write current, reducing the effective power dissipation in the current limiting element. By controlling the duty ratio of the chopped current, the effective current is reduced while the peak current can remain high, significantly reducing heat generation compared to continuous current limiting with a large resistor.
Solution Approach 2:
The patent changes the temporal parameters of the write current by applying chopping modulation. The duty ratio parameter is adjusted to control the effective current value, allowing the system to achieve the same current limiting effect with dramatically reduced power loss and heat generation compared to traditional resistive limiting.
3Reliability
If the power supply voltage is switched to reduce voltage, then the magnetization strength is reduced, but the circuit becomes complicated
Solution Approach 1:
Instead of switching between multiple power supply voltages, the patent uses a single power supply voltage with periodic chopping modulation. The duty ratio of the chopped current controls the effective magnetization strength, eliminating the need for multiple voltage rails and their associated switching circuitry, thus reducing overall circuit complexity.
Solution Approach 2:
The patent changes the control parameter from voltage level selection to time-domain modulation (duty ratio). This parameter transformation allows magnetization strength control to be achieved through temporal modulation rather than voltage switching, simplifying the power supply architecture and reducing circuit complexity.
4Reliability
If chopping current is used to reduce effective voltage, then magnetization strength is adjusted, but fluctuations in the chopping current appear in the magnetized pattern, causing poor waveform reproduction
Solution Approach 1:
The patent carefully designs the chopping frequency and duty ratio to ensure that the periodic modulation does not create harmful artifacts in the magnetized pattern. By selecting an appropriate chopping cycle that is short compared to the reading gap, the fluctuations are minimized and do not appear as significant features in the reproduced waveform, maintaining manufacturing precision.
Solution Approach 2:
The patent uses a chopping cycle that is intentionally made very short (excessive action in terms of frequency) compared to the reading gap. This ensures that multiple chopping cycles occur within the reading gap, causing the fluctuations to average out and not manifest as significant waveform distortion, thereby maintaining good reproduction accuracy.
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 solution enables downsized and cost-effective card readers that produce a favorable reproduced waveform with reduced magnetization strength, maintaining waveform accuracy and compliance with magnetic card standards.
Implementation Method 1
a writing coil 62A that is provided to a magnetic head for recording magnetic data
Implementation Method 2
a reading coil 62B that is separately provided from the writing coil is wound
Data Source
AI summary
A card reader includes a writing coil that is provided to a magnetic head for recording magnetic data in a magnetic card, and a drive circuit that supplies a write current to the writing coil. The drive circuit is a chopping circuit that supplies a chopping current, on/off of which is switched in a specified cycle, as the write current to the writing coil. An on/off cycle of the chopping current is a cycle in which a length of a magnetized pattern in a recording direction is shorter than a reading gap formed in a core around which the writing coil is wound or a core around which a reading coil being separately provided from the writing coil is wound, the magnetized pattern in the recording direction being formed in the magnetic card by the chopping current in a period including one each of the on and the off.