For now though it posed a interesting problem, did I let it run at 6V with the other servo's at a reduced capacity or do I find a way of using them all at their prefered voltages. I could easily purchase a dual output power supply which would server me well in many ways besides the arm but where is the fun in that! I would be passing off a perfect opportunity to learn about the design and construction of a larger dual output linear power supply. The supply itself will be powered from another DC supply, I am not confident enough to make a device that runs from the household 240V AC supply.
So back at the start of November or (possibly the end of October) I started designing my own dual output Linear supply with the following design goals in mind
1: Semi fixed dual channel output.
The voltages I will be using are likely to remain fixed for a long period of time so I want to avoid the possibility that the voltages might be altered without my knowledge by accident. I will include the option of adding a multiturn potentiometer at a later date to make it more flexible and widen its area of use.
2: Modular Construction
I have no doubt I'll find design flaws and areas I can improve upon so I want to break up the primary areas of the power supply so I can easily upgrade them. should I ever decommission the power supply I can reuse some boards in other projects.
3: Run from a 12V DC supply
I have chosen 12V because it gives me the option to power it from a Lead Acid battery and offers a wide range of voltages from 1.25V to roughly 10V. The ability of running the power supply from a car batter means I can finally take the arm away from my desk and make it more mobile, this brings me one little step closer to mu final goal for the arm.
4: Monitor output and input voltages
Despite the output voltages being semi-permanent I still want to monitor them to ensure stability and reliability over long periods. Because of the option to run the PSU from a battery I also want to monitor the input voltage to make sure it stays within 11-13V input.
5: Capable of supplying 5A of current per channel
The arm currently draws 2.5A when all the servo's are under full load, this will increase as I change the servo's from analog to digital servo's. 5A per channel seems like overkill but I would prefer the regulators to be working well within design tolerances than working on their limits.
These were the original five design goals which I set myself but as time passed I added several more goals to the list as it became clear they would be required or simple to include as additional features.
6: Thermal management
Asking the PSU to regulate 5A with a input / output difference of 10V (example: 12V input with 2V output) would produce a insane amount of heat possibly more than my design could handle, even 2.5A with a In/out difference of a few volts would make it too hot to touch after half hour or so.
Because of this I had to include thermal management but I decided not to just screw a 12V fan on the back running full pelt when the supply is idle, I decided to use a thermal management IC that will monitor the two heatsinks and speed up or slow the fan accordingly.
7: Low current fixed output regulators.
Fixed value regulators are easy to implement on their own board for supplying smaller devices, I decided on 5V, 6V, 8V and 9V selectable outputs mainly because they are what I had in stock, I considered a second board with a small LM317 for selectable low current output but shelved this as I already possess several LM317 boards I made in the past for such a purpose.
Right now I have seven PCB's I have designed and manufactured to meet these design goals, I have found some small mistakes and other improvements to be made but nothing that cripples the boards themselves.
The boards I have can be named as,
1: Regulator #1
2: Regulator #2
3: Fixed output Regulator
4: Thermal management
5: Processing (by arduino)
6: Input power control
7: Front panel display
I have taken a fair few photos of the design and construction of the boards to date, far to many to post here so I am instead sharing a link to the gallery with the pictures taken so far, I will update this with more pictures as time passes, check the picture annotations for more info on each picture.
https://picasaweb.google.com/102902771360767231940/DualChannelPowerSupplyProject
Thats all for now, I will write again soon with a circuit diagram of the lot, right now I am keeping it all in my head!
