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Chopper Control Circuit

IP.com Disclosure Number: IPCOM000036704D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Parikh, BH: AUTHOR [+2]

Abstract

Chopping coil drivers eliminate high-wattage limiting resistors and improve electromechanical performance by allowing the coil current to reach the desired level faster. Coil current is limited to a specific value by chopping (switching) the power supply on and off across the coil. The chopping rate can be determined either by the natural time constant (L/R) of the circuit and load or by an external oscillator. Forced frequency chopping, through the use of an external oscillator, eliminates audible noise pollution and provides a tighter toleranced maximum average current and a smaller delta chopping current.

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Chopper Control Circuit

Chopping coil drivers eliminate high-wattage limiting resistors and improve electromechanical performance by allowing the coil current to reach the desired level faster. Coil current is limited to a specific value by chopping (switching) the power supply on and off across the coil. The chopping rate can be determined either by the natural time constant (L/R) of the circuit and load or by an external oscillator. Forced frequency chopping, through the use of an external oscillator, eliminates audible noise pollution and provides a tighter toleranced maximum average current and a smaller delta chopping current.

A basic forced frequency chopping coil driver is shown in Fig. 1. The control circuit block 10, described in greater detail below, generates the chopping logic signal in accordance with the status of three inputs: a DAC input, which is a preset DC voltage that represents the desired maximum coil current; a DIFF AMP input, which is an analog voltage signal that represents the actual coil current; and a -OSC input, which is the oscillator signal that forces the chopping frequency.

(Image Omitted)

The control circuit 10 is shown in greater detail in Fig. 2. The circuit provides reliable capture and limit of the coil current while maintaining the integrity of the chopped current waveform. The disclosed circuit also guarantees that the chopping rate will be at the oscillator frequency even if the loop delay of the circuit exceeds the period...