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  • Author Author: Robert Peter Oakes
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The Modular Bench Power Supply ++, The Essential DIY Build for Every EE Student and Old Timer alike...

Robert Peter Oakes

For every student of Electrical / Electronic Engineering and also the more mature Hobbyist, there is one thing you MUST build for your self at one time or another in your career, preferably earlier on

 

That's a Bench Power Supply and if you don't know how to start or are interested in having a second go at it then welcome to the show, it is going to be a fun and educational ride for all of us.

 

Blog #2 - Voltage References http://www.element14.com/community/groups/test-and-measurement/blog/2014/09/29/voltage-references--the-modular-bench-power-supply

Blog #3 - OP Amps and the Power Stage : http://www.element14.com/community/groups/test-and-measurement/blog/2014/10/04/op-amps-1--intro--the-modular-bench-power-supply

Blog #4 - Displays - Digital and Simple http://www.element14.com/community/groups/test-and-measurement/blog/2014/11/13/the-modular-bench-power-supply--simple-display-setup

BLOG #5 - Power Output Stage (BJT/MOSFET) http://www.element14.com/community/groups/test-and-measurement/blog/2014/11/16/the-modular-bench-power-supply--power-output-stages

BLOG #6 - Basic Unit The Modular Bench Power Supply ++, Putting it all together, the bare bones

Blog #7 - The Modular Bench Power Supply ++ The Input Stage... I want the POWER!!!

Blog #8 - The Modular Bench Power Supply ++, Getting the higher voltages for high side MOSFETS

Blog #9 - The Modular Bench Power Supply ++, More on Displays and using an Arduino to measure Volts and Amps

Blog #10 - The Modular Bench Power Supply ++, Arduino UNO and precision ADC, DAC + MDO3000 I2C debugging

Blog #11 - The Modular Bench Power Supply ++, Differential Sensing and summing junctions

Blog #12 - The Modular Bench Power Supply ++, Integration theory and practical

Blog #13 - The Modular Bench Power Supply ++, testing it all on the bench with the BreadBoard

Blog #14 - Electronic DC Load - Design and Build to test PSU Project

Blog #15 - Electronic DC Load - Performance Improvements

 

So firstly why should every EE build one of these, well for starters it is a very useful tool for any EE to use for prototyping, testing and many other things from Battery Charging to help test the power limits of a new control system

the second and an equally important reason is it provides numerous opportunities to learn some great skills regarding controlling power, feedback loops used for current limits and voltage stability, you can learn the difference between Accuracy and Stability (Which do you think is more important for a voltage reference in a power supply, well you will find out).

 

So who am I to show you how. Well I'm a certified electronics engineer who went through an apprenticeship in the north of England with a great company called Welwyn Electric (Now I believe part of the Vishay group). Anyway I learned my trade there and also had the awesome opportunity to work in a second level Calibration LAB where I got to play with all sorts of electronics equipment to numerous to list, learning how to calibrate them way beyond the manufacturers standard cal procedures but I also learned the value of having certain good equipment to help with project design, testing and maintenance. A good Meter, Scope and Power Supply, the first two are out of reach as a tutorial but the supply is not. I built my first one when I was 17, there were no micro-controllers, no LCD Displays, it was all analogue and Moving Coil Meters... Ah those where the days.

 

Anyway, the whole process from designing it, figuring out why things worked the way they did and also how to improve on the design over time to make it more accurate, more stable and provide more power was always a great learning opportunity

 

Now I wish to share this with everyone on a new and improved Modular Bench Power System, and when I say modular I mean modular. I have seen so many designs claiming to be modular but in reality it is one design and one fixed result. Some good and some bad.

 

Element 14 has been kind enough to sponsor me for this project and I will be providing links to all the components used in he project so you can also use the same if you so desire.

 

What I am planning is a power system that can be as upgradeable as most desktop computers (Need a new video card, great, swap out the old for new, need a better CPU, Same thing). In our case each significant module of this power supply will go through two or more versions as we ride the project to its destination. My Target destination anyway, you will be welcome to ride all the way with me or get off part way through depending on your budget and time. Oh and of course you can also stay on the train and take it beyond my design and make it yours. and you don't have to do everything, there is plenty of opportunity to mix and match as we go.

 

by now yo may be wondering, why do I keep calling it the Bench power System and not Supply, well this is why:-

 

My ideal target specifications

There will be three significant parts that can be built as separate projects or included into the Power System

Dual Channel Power Supply each outputting 30V @ 4A or 15V @ 8A, user selectable, independently adjustable

DC Load 60V /10A (But not 600W image ) controlling  Volts and Current

Power Meter showing Watts, Watt Hour, Volts, Current

Battery Charging Profiles

Logging on all modules above

Network and USB support for LXI and VISA protocols (SCPI)

All modules controlled by micro-controller/s with a master control unit based on embedded Linux

4" touch screen display / control

Speech Output

 

Not all of the above features are needed or essential, and there is no need to build yours to the same specification, I will tell you where the opportunities are to put in parts to meet your budget and requirements

 

The main power supply is broken down in to several sub modules as follows

 

Voltage Reference circuit, providing feeding the other modules

DC Power, this module converts the mains supply to a safe and smooth voltage for the rest of the supply

Output Driver. This module will be  power transistors providing the actual limiting of the output to supply channels

Output and Sense, this is the actual output and also the voltage sense circuit needed for control

Voltage Control module set and vary the desired output voltage of the supply

Current control module will allow the user to pre-set the current limits of the power supply outputs

Displays and Controls, how else will you see and adjust things image

 

We will start with the basics, a backgrounder on the modules purpose and basic functionality, the simpler analogue design and accurate enough for basic projects, this will help you understand Voltage references, OP-AMPS, feedback loops, Curent shunts both high side and low side and the benefits of each

 

Later, once we have the basic PSU working, we will upgrade modules to improve the regulation, accuracy and then some form of digital control in the form of a micro-controller, at this point we will discuss ADC, DAC resolution, over sampling etc.

 

This is a block diagram of the first modules we will tackle:

image

Oh and don worry if your unsure of handling mains voltages , there will be an option to cover that off too, I don't want to put anyone in harms way or take them out of their comfort zone (If your new to electronics and don't have experienced help, take the simpler approach I will present)

 

Oh, just so were clear. not all the designs are complete, only the concepts and target specifications are known at this point, I have many parts selected based on experience but what we end up with is unknown at this time and like I said at the beginning, its going to be a fun ride. So buckle up and get the soldering irons tuned

 

So what do you think, I'm open to ideas and nothing too crazy will be rejected from the considerations pile, if there is something you would specifically like covered, let me know

 

I look forward to your input and support

 

First lesson coming soon all about Voltage References.

Parents

  • Hello, First off great video series im eager to so the completion. I have a few questions, first in your original plans you only use a single dual op amp but the revised which i am have difficulty understanding uses 4 op amps 2 for voltage control and 2 for the adjusting.? two if at all possible do i have to install the second set of op amps for this supply to work? i am currently to the build stage when looking back through i seen the updates plans i was like sun of a gun. if i need to build the second set of op amps thats ok i have a lm3224n ill use. third any chance you can post the revised plans but in the same format as original? sorry if that is a stupid request but for some reason im having a heck of a time reading it. Thank you.

  • in reply to omnacron

    ok i feel like a idiot. i realised that i missed the link for the parts of the plans i missed. But my question is do i need this extra sensing atm im not looking for super fine control (budget restraints)?

  • in reply to omnacron

    The op amps can be divided into two camps, one for Current (2 Op Amps) and one for Voltage (Again 2 op-amps), the first op amp of each is used to up the voltage sensed to the same range as the reference wich in this case was 0-5V, the second op-amp of each stage is used to integrate the summing junction just after the first op amp in order to know if it is needed to drive the FET more on or turn it off.

     

    the very early diagrams can be used where I have only single op-amps, the design will not perform quite so well but will be more than enough for most situations, I will have a look back and see if I have a diagram suitable for your needs

  • in reply to Robert Peter Oakes

    thank you for the quick reply. Thank you for the information now i understand a bit more. I had a idea to help with any heat issues i'm wanting to install a 120mm fan on the enclosure but im not sure were to install the 12v regulator i was think of running from the main rails before the input to the voltage ref or from the supply rail to the op amps. i'm thinking just using to use a standard 7812, little  worried about heat though. My power system in running at 32.56 volts dc no load at the output. and i have one more idea insteading of risking to more heat in the 7812 i could install a second smaller transformer it is a 11 wire transformer that could 5v to 30 volt depending on wire combo. Sorry if it seems i'm rambling i guess spit balling ideas to myself. Anyone have any thoughts. oh wait i am wondering if i use a quad op since i'm only going with the early version what else could i add onto the supply that could utilize the other 2 op amps or is that a bad idea.

Comment
  • in reply to Robert Peter Oakes

    thank you for the quick reply. Thank you for the information now i understand a bit more. I had a idea to help with any heat issues i'm wanting to install a 120mm fan on the enclosure but im not sure were to install the 12v regulator i was think of running from the main rails before the input to the voltage ref or from the supply rail to the op amps. i'm thinking just using to use a standard 7812, little  worried about heat though. My power system in running at 32.56 volts dc no load at the output. and i have one more idea insteading of risking to more heat in the 7812 i could install a second smaller transformer it is a 11 wire transformer that could 5v to 30 volt depending on wire combo. Sorry if it seems i'm rambling i guess spit balling ideas to myself. Anyone have any thoughts. oh wait i am wondering if i use a quad op since i'm only going with the early version what else could i add onto the supply that could utilize the other 2 op amps or is that a bad idea.

Children
  • in reply to omnacron

    I would use the op-amps in the way of th elater diagrams, you will have a better power supply

     

    the fan should not be connected close (Electrically) to the op amps as it will inroduce noise into the circuit, feed it seperatly from the main supply through its own regulator, or even a variable regulator so you can control the speed to a limited extent.

  • in reply to Robert Peter Oakes

    Hello just wanted to post a update on my build of the power supply. well i have everything setup and connected for the most part i was doing some testing and i have ran into a wall. My problem is with my voltage ref. i'm using a 5.1v zener with a mosfet using 2 100 ohm resistors from the source to zener and a 10k to the gate i'm getting a stable 5.92v well i was till my 2x 100 ohm's decided to go up looking like a volcano lol. i realized that 1/4 watt resistors were not going to cut it so i am using 1/2 watt only thing i have. and even those are cooking with nitro temps around 131 f. i have a cooling fan running on them so there still quite warm but not burning up atm. The aggravating thing is that once i went from the breadboard i have lost my control of the voltage and i think i ruined my zener so i pulled the whole voltage ref circuit out and re breadboarded it with the 1/2 watt resistors and a new zener and used test leads to attach it to my supply and it worked transferred it back and no voltage control and my voltage ref dropped down to 3.2 mv its very aggravating tomorrow i will remove the circuit again and try it again. just to give some info my supply after rectified im getting 36.8v the current i don't know as of yet i'm estimating ti to be around 6-8 amps i wont know till i get it working and use my meter to test the current.all the parts the i'm using for this build are salvaged parts except for the resistors and the zener which if i did blow it im down to my last roflmao just my luck. anyways any ideas on how i can beef up the voltage ref? just please keep in mind by budget is literally zero cause of health problems im un able to work. i have allot of parts so if its some that could be salvaged i might have it. thank you for your time and patience. oh and the voltage readings at the output are 31.8 volts

  • in reply to omnacron

    Well the voltage reference is for sure the most important part to get right, without it, the rest will be worse.

     

    So a 5.1V zener from 38V is leaving 33V to drop across the resistors

     

    simple math I=V/R = 33/200 = 165mA... too much current or way more than needed anyway.

     

    33V * .165mA = 5.4Watts, so even over 2 resistors your 1/2 watt ones are no where near big enough, also you dont need that much current through the Zener, only 15-20mA would be enough so increase the resistors to 1.5K or 2K ish, this will also reduce the power to 0.66W total or 330mW per resistor

     

    Dont know what brand of Zener your using but this one is a typical one TZX5V1B-TAP VISHAY SEMICONDUCTOR Diodes - Zener Single | 20H7297 | Newark element14 Canada and only requires about 5-10mA so the 1.5K-2Kohm resistor will do the trick, or two or three lesser resistance that adds up to this value in series (or slightly more depending on your zener needs will spread what little heat there will be.

     

    also if your not getting the volts in circuit as you do on the breadboard, there is sure to be something wrong with the wiring, check voltages before the zener is installed to be sure rahter than risk frying it, if you have a meter then measure the current where the zener should be, it should only read about 20mA is depending on the resistors and the  main rail voltage of course (Simple Math I=V/R so 38/2000 = 19mA)

     

    I also used a JFET, not  a mosfet int he zener regulator circuit so this could also be affecting what your doing, can you provide a schematic of this part of the design for me to see

  • in reply to Robert Peter Oakes

    Thank you for the quick reply. ill increase the resistors and check the current flow were the zener should be. im using a STP55NF06 for the voltage ref. and the zener is just one from radio shack ill have to look it up. im using two of the STP55NF06 the one for the voltage ref and the other for the main output.

  • in reply to omnacron

    Thats an N CHannel MOSFET and will not replace a JFET, how are you using it (Schematic will help here) ?