DIY Project: Regulated DC High Voltage Power Supply For Your Lab

This DIY project is addressed to all the tube audio freaks outside. I will show you how to build up a regulated high voltage DC power supply for your laboratory.

The features will be:

• Voltage: 0 .. 400V
• Current: 0 .. 0,5A
• Short circuit proof
  
• Interlock relay and switchable outputs for safety
• Circuit diagram, PCB and optional software under GPL
  

Optional:

• Serial and/or USB interface for easy lab automation.
• Display showing mode of operation and actual values

Part 1 - Preliminary Thoughts

My development goal is to have a power supply for the development of tube equipped high end audio circuits. It should be possible to connect 2 units in series or parallel, depending on the needs of the circuit under development. Output voltages up to 800V and output currents up to 1A could be obtained from such a setup.

The purpose sets some tough goals: high precission regulated outputs, quickly reacting on changes. Extraordinary low noise. Easy yet safe handling.

These goals are contradictionary to some degree. A very fast reacting device has often a poor DC precission. Offsets and drifts are typical. This could lead us to a compound arrangement. A fast amplifier ensures quick reaction and a second precise amplifier corrects DC issues. We will see later how this problem has been solved.

Extraordinary low noise is difficult to achieve with switching power supplies. This points us to a linear regulator. On the other hand a SPS has a far better efficiency but is much more complicated in design. I will use a technique to reduce the heat dissipation of the power supply but the regulator itself is a linear scheme.

Filtering of inputs and outputs is an important part when you want to get a high quality power supply. I will set some spot lights on techniques how to get the currents 'clean'.

The last chapters are dealing with the microcontroller who enables us to program and remotely control the power supply. Integration into automatic test equipment or a programmable tube tester are now in reach.

Part 2 - The Mains Input Section

Lets face it: the mains input is a dirty place to live for sensitive electronic equipment. The AC voltage is not suitable to supply semiconductors and all the noise and disturbances are presenting high demands for filters and regulators.


A power supply capable of delivering 200W (400V x 0,5A = 200W) can waste a lot of energy by heating the environment - your lab. Effective means to control the heat are required.

Power lines are contaminated with noise of many different sources. From very low frequencies up to the GHz range all kinds of signals can be found.The energy contained within these signals varies also from hardly to detect up to destructive levels.

HowTo use USB inside Sun VirtualBox non-OSE on a Linux host

Situation:

You have installed the non-OSE version of Virtualbox on Linux. Your Guest-OS, i.e. Windows, is installed but you cannot access connected USB-devices. Your USB equipment is displayed grayed out, you cannot check it.

Solution:

The solution to this issue consists of the following steps:

1. If VirtualBox is running, shutdown the guest-OS and close Virtualbox.
2. Make sure you have the non-OSE version of virtulabox installed. openSUSE installs by defaut the OSE version, which is not USB enabled.
3. Open the file /etc/init.d/boot.local as root and append the line
   
   /mount -a
   
   Save the file.
   
   
4. No we need to figure out the group-ID of vboxusers. Open a textconsole window an enter:
   
   grep vbox /etc/group
   
   You should get a response like:
   
   vboxusers:!:109:robert
   
   109 is the group-ID. It might be different in your case. Remember the number, we will need it later.
   
   
   
5. Open the file /etc/fstab as root and modify it as follows:
   
   The entry starting with usbfs is commented out by placing a # in front of it. So it looks like # usbfs ...
   
   Add an new entry:
   
   none /proc/bus/usb usbfs auto,busmode=0775,
   devmode=0664,busgid=xxx,devgid=xxx 0 0
   
   Note: The two lines above should appear as one line in your fstab file. Do not place spaces before and after the colons. I have inserted a break for better readability.  Of course you have to replace the 'xxx' strings by the number you found in step 4.
   
   
6. Do you remember the output of step 4.? Did it state your user name as shown in my example? If so proceed with step 7. If not you have to add your username to the group vboxusers. You can do this with the group management tool of your distro or by typing the following into a text console as root:
   
   groupmod --add-user xxx vboxusers
   
   In this line you have to replace the 'xxx' by your username. Do not insert the group-ID from step 4. here!
   
7. If you have previously started VirtualBox some tmp files should be removed. In order to do so enter the following as root at a text console:
   
   rm -r /tmp/.vbox-xxx-ipc/
   
   As in the example above, the xxx is a placeholder and must be replaced by your username.
   
   Be careful while typing the rm command. rm -r (-r = recursive) has the power to destroy working installations!
   
   
8. Now we are comming to the final steps of this HowTo.
   
   Open a text console and enter as user:
   
   env VBOX_USB=usbfs /usr/bin/VirtualBox
   
   At the VBox control panel scroll down to the USB section and click it. Activate USB controller and USB 2.0 controller. Add at least an empty USB filter (the topmost icon right beside the listbox). Quit this window by clicking OK. Now start the guest OS and check the USB devices. Of course you should have connected an USB device...
   
9. Typing the whole string
   
   env VBOX_USB=usbfs /usr/bin/VirtualBox
   
   in order to start VBox is very unconvenient. A desktop icon would be a good place to keep this command.
   

My Motivation:

I installed Virtualbox in spring 2008 for the first time. Installing Windows XP was no problem. And I could use some apps which have no counterpart on linux. As I wanted to use an USB scanner for the first time I struggled. Lots of googleing finally gave me all the information I seeked that time. Each website presented a part of the puzzle. But no one showed the whole game.
Now I have a functioning scheme which is tested on different computers running openSUSE 11.0 and 11.1 as 32 bit as well as as 64 bit versions.
Hopefully this short text will be of use for you.

Copyright

This HowTo is based on many publications on different websites. I collected them during 2008. The solely applicable license is the GNU Public License (GPL).