Tag Archives: Current

Protecting the USB from over voltage and overcurrent threats


An application note from Littelfuse about USB protection.

This application note addresses the various requirements for protecting the Universal Serial Bus (USB) from overcurrent and overvoltage environmental threats. The solutions presented cover both USB 1.1 and the higher speed USB 2.0 circuitry. Specific emphasis is placed on USB 2.0 with information directed at hot connection over current conditions and electrostatic discharge (ESD) induced in the USB system.

Protecting the USB from over voltage and overcurrent threats – [Link]

Measure small currents without adding resistive insertion loss


by Maciej Kokot @ edn.com:

In most cases, you measure current by converting it into a proportional voltage and then measuring the voltage. Figure 1 shows two typical methods of making the conversion. In one method, you insert a probing resistor, RP, in series with the current path and use differential amplifier IC1 to measure the resulting voltage drop (Figure 1a). A second method is a widely known operational amplifier current-to-voltage converter in which inverted IC1’s output sinks the incoming current through the feedback resistor (Figure 1b).

Measure small currents without adding resistive insertion loss – [Link]

USB power supply active load tester


Sasa Karanovic has designed and built a DIY USB power Supply active load tester, that is available at GitHub:

USB Power supply Active Load Tester or short PAL Tester is unit designed for testing the quality of the power supplies.
Idea was to create low-cost, precise device for simultaneous measurement of Voltage and Current drawn from the device under test.

USB power supply active load tester – [Link]

Current monitor uses Hall sensor


by Paul Galluzzi @ edn.com:

The Fig 1 circuit uses a Hall-effect sensor, consisting of an IC that resides in a small gap in a flux-collector toroid, to measure dc current in the range of 0 to 40A. You wrap the current-carrying wire through the toroid; the Hall voltage VH is then linearly proportional to the current (I). The current drain from VB is less than 30 mA.

To monitor an automobile alternator’s output current, for example, connect the car’s battery between the circuit’s VB terminal and ground, and wrap one turn of wire through the toroid. (Or, you could wrap 10 turns—if they’d fit—to measure 1A full scale.) When I=0V, the current sensor’s (CS1’s) VH output equals one-half of its 10V bias voltage. Because regulators IC1 and IC2 provide a bipolar bias voltage, VH and VOUT are zero when I is zero; you can then adjust the output gain and offset to scale VOUT at 1V per 10A.

Current monitor uses Hall sensor – [Link]

Using the cirrus logic CS5464 for AC current measurement

Using the cirrus logic CS5464 for AC current measurement by Corgi-Tronics:

Continuing the series on examining devices to measure AC current, this time we’ll try out the CS5464 from Cirrus Logic. I initially built it up on a breadboard, but I’ll skip writing up this test and instead build up a prototype and run AC line power through it.

This is a Three-channel, Single-phase Power/Energy monitoring chip, and also can use current shunts and is intended for power meters.
This device provides no direct isolation, instead the entire device (input and output) directly coupled to the AC power line. Any isolation must be provided separately.


Using the cirrus logic CS5464 for AC current measurement – [Link]

A simple current-sense technique eliminating a sense resistor


An old but interesting app note (PDF) from Microsemi on resistorless current-sensing technique. [via]

This application note introduces a simple current-sense technique that eliminates that sense resistor, resulting in system-cost reduction, PCB space saving, and power efficiency improvement. Furthermore, the new current sensing mechanism allows higher dynamic tripping current than the static one (built-in low-pass filtering) to improve current-sense noise immunity.

A simple current-sense technique eliminating a sense resistor – [Link]

Sensing Elements for Current Measurements


by Ryan Roderick, Intersil @ edn.com:

The fundamentals to translating the analog world into the digital domain reduces to a handful of basic parameters. Voltage, current, and frequency are electrical parameters that describe most of the analog world. Current measurements are used to monitor many different parameters, with one of them being power to a load.

There are many choices of sensing elements to measure current to a load. The choices of current sensing elements can be sorted by applications as well as the magnitude of the current measured. This write up is part one of a three part series that discusses different types of current sensing elements. The focus of this paper is evaluating current measurements using a shunt (sense) resistor. The paper explains how to choose a sense resistor, discuss the inaccuracies associated with the sensing element and the paper discusses extraneous parameters that compromises the overall measurement.

Sensing Elements for Current Measurements – [Link]

Building a constant current/constant power electronic load


Kerry Wong built a DIY constant current/constant power electronic load. It can sink more than 200W of power:

A while back I built a simple constant current electronic load using an aluminum HDD cooler case as the heatsink. While it was sufficient for a few amps’ load under low voltages, it could not handle load much higher than a few dozen watts at least not for a prolonged period of time. So this time around, I decided to build a much beefier electronic load so it could be used in more demanding situations.
One of the features a lot of commercial electronic loads has in common is the ability to sink constant power. Constant power would come in handy when measuring battery capacities (Wh) or testing power supplies for instance. To accommodate this, I decided to use an Arduino (ATmega328p) microcontroller.


Building a constant current/constant power electronic load – [Link]