The variable High-Voltage Power Supply Schematics
Power supply: 0-1kV5 with HV module
Power supply: 0-3kV
Another power supply: 0-1kV for GM tubes
Calibration of the detector:
Start with 600 Volts and slowly raise the voltage until it starts to
register counts. This is the threshold voltage of the Geiger elements.
Increase the voltage until you reach a point where the count rate levels off.
All ionizing particles will now be detected. This 'plateau' should
extent for several hundred volts. As you raise the voltage
higher, secondary effects will produce counts too. Set the voltage
at the center of the plateau.
Variable High-Voltage Power Supply with ready-made Module
UPDATE 13-09-2005: As stated below, those ready-made high-voltage power supply modules make easy, hassle-free
power supplies.
The HV module is a 12VDC/1kV5 proportional type available from several companies. The LM317T is a variable
voltage regulator, which supplies the HV module. Use a 10-turn potentiometer for R1 for sufficient accuracy when
adjusting the voltage. The input voltage must be slightly higher than 12V due voltage drop of the LM317.
NOTE: If you use a potentiometer (R1): Only suitable for uncritical operation, such as our flat detectors or GM tubes.
I.e. do not supply photomultipliers (PMT's) with it! If the slider of the potentiometer has no contact, the output
voltage can contain spikes up to the max. voltage of the module. If you replace the potentiometer (R1) with a trim-pot for
one-time calibration or a fixed resistor, it is suitable for supplying a photomultiplier tube aswell.
UPDATE 18-09-2004: Building the power supply yourself is fun, but ready-made high-voltage power supply modules, which are available for about 100USD
for 1.5kV versions, are the better solution in my opinion.
The variable High-Voltage Power Supply 0-3kV Schematic
You'll need a variable high-voltage supply to operate the detector.
 |
 |
Heat sink for
2N3055 and
BU208 |
The transformer is uncritical and easy to build. Use a E or EI core without
air gap with an AL value of approx. 2000nH/W2. The primary
coil has 25 windings of 0.7 - 1 mm magnet wire; the secondary coil has
500 windings of 0.2 - 0.3 mm magnet wire. Make sure that the insulation of the primary
and secondary coil is well done. You should only use a plastic bobbin (Wickelkern in german)
with 2 chambers - one for the primary coil the second chamber for the secondary coil.
UPDATE 24-01-2004:
Further testing of the power supply produced the following results:
Sometimes there are startup problems of the 20kHz oscillator.
UPDATE 14-02-2004:
The power supply works just fine! I put a hose clip (german: Schlauchbinder) around the ferrite core and now
it is much more quiet! Earlier I measured a voltage of only about 25V (over a resistor voltage divider), which is
about 1500V at C6 - unfortunately the (cheap) multimeter has an internal resistance of only 1MOhm, so this reduced
the measured voltage to about the half! So be careful choosing the multimeter when measuring over a high-ohm
divider. I then used my expensive multimeter and voila! I get about 60V, which are 3500V at C6. 8-)
0-1000V Regulated High Voltage Power Supply
Another power supply that can be used for the Geiger-Müller tube variant of the cosmic ray muon detector.
If the specific transformer mentioned in the schematic is not available to you, any transformer
with the specifications primary 117VAC, secondary 6.3VAC CT (center-tapped) should work.
In this case you might have to choose a different drive frequency in order to operate at the sweet spot
of the transformer:
"[...] I found in driving a transformer as is done in this project that the overall performance varied
significantly as I varied the drive frequency. In a series of experiments I loaded the transformer
directly with a variable resistor (no rectifier used), measured the AC voltage across this resistor,
measured the DC current into the transformer, and varied the drive frequency. I looked for a frequency
where the output voltage was highest and the input current was lowest. [...] 'ripple' is roughly +/-25V
for output voltage >200V. This ripple isn't sinusoidal at all. It is basically a spike then monotonically
decays until the next spike."
I cannot be held liable for damage of any sort! Be very careful when handling
high voltages!
Last-Modified: Tue, 13 Sep 2005 22:02:32 GMT
Be very careful when handling high voltages!
cosmicrays.org cannot be held liable for damage of any sort!
|
