The Modular Bench Power Supply ++, Differential Sensing and summing junctions

28 May 2015

Back to the Main post The Modular Bench Power Supply ++, The Essential DIY Build for Every EE Student and Old Timer alike...

It has been a few months since my last post on the Power supply Project so here are a few in quick sucession

Up first is a view to sensing the Current and Voltage of the PSU using a differential configured OP amp

In the videos I will walk you through the functionality of the design and also demonstrate the curcuit working on the breadboard

Some of the features I wanted to utilize where

Jellybean components for the passives and chips

keep the gains to low figures and also the BOM to a low count if possible

Float the analogue control on the positive rail of the power supply, while this necesatates the need for an additional power supply for the control power, it simplifies the design because there is no level shifting required and the op amps do not need to be rail to rail or able to work at a high voltage, this allows for less expensive parts to be used

you will notice that many resistors have two in series where one might do. The reason for this is to show that even with basic range resistor values you can still get fairly accurate control of gain, resistor dividers and other functions without having to resort to more expensive components

It is worth noting though that in some cases I have shown for example a 18R resistor in series with a 18K resistor. the resistors I used in the practical are 5%, the 18R does not compensate for 5% error so it would be worth simply measuring the primary resistor and then picking the addition to go withit based on what the real value is. If you going to drive the control using a DAC / Microcontroller then of course this can all be calibrated out using software.

Here is the schematic I finally ended up with for the two differential amplifiers. Remember they will be floating on the + rail of the Power output.

Voltage Sensing: