This page shows some basic information on - High Side Current Monitors such as the Zetex - ZXCT-1009 integrated circuit.
The first circuit is a current monitor made with an LM358 OpAmp. While functional, the three diodes in the supply line make it unsuitable for most applications.
Diodes D1, D2 and D3 are used to ensure that the voltage at the input terminals is at least two volts lower than the amplifiers supply voltage. This is undesirable as the voltage to the load is reduced and power is wasted as heat produced by the diodes.
The circuit is good for experimenting as it can be made from readily available parts.
The next circuit uses an integrated circuit that is specifically designed for this application. There are a number of manufactures of these devices and there is also a considerable variety of features that can be had from specific IC's.
Due to the internal circuitry of this device, no diodes are required in the supply circuit.
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.
31 December, 2009