Current Sense Resistor Research Articles

Effect of a current-sensing resistor on required mosfet size

The effect of a current-sensing resistor used in current-mode control of pulsewidth modulator (PWM) converters on required MOSFET aspect ratio, the ratio of channel width to channel length generally known as W/L, is studied. The results can also be applied to the effect of source parasitic resistance in a power MOSFET. These resistances require a significant increase in aspect ratio to achieve a desired maximum current capability. Experimental results are presented verifying the validity of the theoretical results.

Conductivity and Time-Constant Measurements on Magnetically-Agitated Electrophotographic Developer Using the Method of the Compensated Probe

The general concept of developer “conductivity” is known to play a role in development rate and efficiency, but a packed powder cell measures conductivity under conditions quite different from an actual toning nip. For a two-component developer with magnetized carrier, the developer is magnetically agitated as it flows through the toning zone, while in the packed cell it is static. A test cell was constructed which agitates a thin layer of developer and subjects it to brief voltage pulses, as it would realistically experience in a nip transition. In many cases of interest the developer is insulating enough that most of the current is capacitive, making actual toning current difficult to discern. This particular problem can be overcome by designing the measurement circuit as a compensated probe, that is, with a capacitor in parallel with the current sense resistor. Example waveforms give evidence of a nonlinear conduction process in toning.

A high-current very wide-band transconductance amplifier

A novel design approach for a high-current, very-wide-band transconductance amplifier is described. The approach is based on paralleling the input and output of complementary unipolar current-mirror cells. Each cell has a fixed current gain determined by the ratio of two resistors. A differential input voltage-to-current circuit drives the cell array. The design avoids the need for a single low-resistance current-sensing resistor and the attendant problems inherent in such resistors. Although the concept is still under development, a prototype of the cell-based transconductance amplifier was implemented with ten positive and ten negative current cells to gain some experimental familiarity with the approach in addition to providing verification of computer simulation results. The prototype transconductance amplifier is DC coupled, has a 3-dB bandwidth of about 750 kHz, and can deliver up to 35 A RMS (root mean square) at 100 kHz with an output compliance voltage of 5 V RMS. Other important characteristics such as output-load regulation and DC offsets are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A versatile system for inelastic electron tunnelling spectroscopy

A spectrometer system for sensitive measurements of inelastic tunnelling spectra is described. Modulation and bridge techniques are used to determine the current I, and the derivatives dI/dV and d2I/dV2 for a four-terminal tunnelling junction subject to an applied bias potential V. An operational amplifier circuit sweeps the DC bias voltage across the sample whilst holding the superimposed AC modulation voltage constant, independent of conductance changes. The current I and dI/dV are determined using DC and lock-in voltmeters connected across a current-sensing resistor, whilst a bridge configuration permits low-noise measurements of the second derivative. The bridge may be automatically balanced over the entire range of bias voltage using a voltage-controlled resistor and feedback, thus minimising source noise. The circuitry is designed to operate in association with a microcomputer which permits signal-to-noise enhancement by signal averaging. A dummy sample based on p n junction is used for test and calibration purposes.

Regulator to Control Current Sharing among Parallel-Connected Power Transistors

A current regulator is described that controls the peak current of a power transistor driving an inductive load, such as magnet coils. Presently, the current pulse has a 0.1- to I-ms adjustable duration with duty cycle to 5%. Ultimately, the pulse length must be ~ 7 ms with 50% duty cycle. The peak current nominally is 200 A, as set by a reference pulse. Several transistors, each controlled by an individual regulator, are connected in parallel to provide the total peak load current. The regulators compensate for differences between the power transistors and assure equal current sharing among the collectors. The regulator comprises an 8-bit multiplying digital-to-analog (D/A) converter that drives the base of the power transistor, an 8-bit up-down counter, an analog differencing circuit, and a comparator. For control purposes, a current-sensing resistor in the transistor's collector produces the second input to the differencing circuit. Regulation is accomplished over a collector current range of 200 ± 50 A per stage.

Dialable ampere current source with ovenless construction and ppm/h stability

This paper describes the design and construction of a highly stable, dialable current source developed for use with an electron beam transport system. The current regulator is ovenless and employs thermal feedback to cancel effects of ambient temperature variation and self-heating in the current-sensing resistor. The regulator is of modular design and incorporates remote control features to facilitate use in applications requiring many current channels. The output current can be modulated to permit Monte Carlo beam optimization. The output stability is better than ±1 ppm/h at an output current of 1 A, in an environment subject to ±1 °C temperature variation, measured using instrumentation having a nominal stability of ±1.5 ppm/h.