Experiment 17 (24/05/05) - HVPS-PRO Power supply for research experiments

Engineer Xavier Borg - Blaze Labs Research 24/05/05

The 50kV lab supply that connects to your PC, displays voltage & current and more...

This is a newer & improved version of all previous designs, with more electronics and lighter design. To our knowledge, it is indeed the lightest HV lab power supply one can find, fully loaded with new features, uses the latest technology electronic components and which runs from a single 12v cell/ supply at a conversion efficiency exceeding 91%. With this supply you have control over pulse depth, frequency, pulse width and dc offset level, thus generating a huge variety of output waveforms for different HV research work. If the on board wave functions are not enough, an external waveform generator can be connected to its modulation input and the hv output will follow the required wave function. The supply can be remotely controlled via an optoisolated TTL logic input, which can be directly & safely connected to your PC parallel port or any 5v TTL logic circuit. Voltage regulation is efficiently digitally controlled with an onboard PWM feedback SMPS, which continously tracks the output voltage. This eliminated the need for the heavy duty transistors together with the heatsinks that were required in the series regulator used in previous versions. This control is also utilised to set the output voltage anywhere from absolute zero to a maximum voltage of 50kV with great precision. In this version, a dual digital readout is included, simultanously displaying output current (in mA) and voltage (in kV) even if you are not equipped with an hv probe. This reduces the wiring and external instruments which one usually has to setup in between his power supply and load whilst giving both voltage and current readings at a glance.

As with the HVPS0x series, its output can also be pulse width modulated with the onboard oscillator from 1Hz to 1kHz, with duty cycle fully variable from 0% to 100%, and pulse amplitude setting from 0% to 100% of the rated voltage, thus enabling any pulse voltage amplitude to be set. It also senses load current and boosts the power output accordingly, making the unit over 91% efficient over the whole range and reducing power consumption under no-load conditions. It has also a low and high voltage shutdown which disables the unit when the input voltage is out of its operating range. The weight for this supply is just 500g and requires only one external 12v battery to operate at its full rated output. This unit can be alternatively powered by solar panels, or a capacitor bank, delivering a minimum of 250mA at 13.5v. Unlike other power suppies on the market, no charge pump is utilised on its output, thus making the output safe to touch immediately after switching off, with no need to discharge it to ground.

HVPS-PRO supply 24.05.05


50kV Lab HVPS-PRO waveforms
On-board waveform generator traces

The unit is will automatically shut down when the battery voltage is below or above the specified voltage range and resumes operation when the voltage recovers to its normal operating range. The on board electronic streamer/ spark detector has been incorporated to instantly reduce the voltage until the streamer/ spark is below a preset current level of 3mA. Further enhancements include input reverse polarity protection and protection against high current discharges entering the negative hv probe.

The supply is controlled by 4 plastic track precision potentiometers, Pot 1 to 4. Pot 1 sets the frequency of the on-board oscillator ranging from 1Hz to 1kHz (Fig 1 to 3). Pot 2 varies its duty cycle from 0% to 100% (Fig 4-6). The figures 4,5,6 show three different waveforms as pulse width is increased through 10%, 50% and 90%. When fully anticlockwise (0% duty cycle) or fully clockwise (100% duty cycle), no pulses appear at the output. Pot 3 sets the amplitude of the pulse output voltage from absolute zero to full maximum voltage (Fig 7-9). Pot 4, actually offsets the pulse over any dc voltage level from 0 to 50kV (Fig 10-12). Shown above are a few of the output waveform combinations that can be obtained with this unit. In the order top to bottom, figures 1,2,3 show varying frequency, figures 4,5,6 show varying duty cycle, and figures 7,8,9 show varying pulse amplitude, Fig 10,11,12 show dc offsetting, Fig 13,14,15 show dc offsetting when pulse amplitude is null. Further to the combinations offered by the on board generator, the external modulation input feature enables an external waveform generator to control the hv waveform to any other desired function.

Technical specifications for HVPS-PRO
Input voltage13.5v (nominal)
Low input voltage cut off11.5v
High input voltage shut down15v
No load input power3 Watts
Reverse polarity protection10A fuse + diode
Max continous power80W
SMPS Efficiency91%
Overall Efficiency80%
Output voltage0 to 50kV @ 13.5v dc
Max output voltage50kV
Max pulse amplitude50kV
Max dc offset50kV
Min pulse amplitude0kV
Min dc offset0kV
Output voltage type+dc
Output impedance1E6 Ohms
Streamer protection threshold3mA
Current limit4mA
Overboost current threshold0.5mA
Voltage digital readout (kV)3 digit
Current digital readout (mA)3 digit
Voltage readout resolution±0.1kV
Current digital readout±10uA
Current sensinghv shunt
Pulse frequency1Hz to 1kHz
Pulse duty cycle0 to100%
Digital inputOpto isolated 5v TTL negative logic

Notes on controlling HVPS-PRO through your PC parallel port

A PC parallel port is 25 pin D-shaped female connector in the back of the computer. It is normally used for connecting computer to printer, but many other peripherals for this port is available today. The HVPS-PRO is one such device.

Not all 25 are required, in fact all you need to control HVPS-PRO are just two of them. All you need to know is which are the ground and data pins. A parallel port has 8 output data lines and signal ground.

Pin Function

             Register  DB-25     I/O   
Signal Name    Bit      Pin   Direction
===========  ========  =====  =========
-Strobe        ¬C0       1      Output 
+Data Bit 0     D0       2      Output 
+Data Bit 1     D1       3      Output 
+Data Bit 2     D2       4      Output 
+Data Bit 3     D3       5      Output 
+Data Bit 4     D4       6      Output 
+Data Bit 5     D5       7      Output 
+Data Bit 6     D6       8      Output 
+Data Bit 7     D7       9      Output 
-Acknowledge    S6      10       Input 
+Busy          ¬S7      11       Input 
+Paper End      S5      12       Input 
+Select In      S4      13       Input 
-Auto Feed     ¬C1      14      Output 
-Error          S3      15       Input 
-Initialize     C2      16      Output 
-Select        ¬C3      17      Output 
 Ground          -     18-25       -   
(Note that the S7, C0, C1 & C3 signals are inverted logic)

IBM-PC Parallel Printer Port Female DB-25 Socket external Pin layout

/                                                      \
\  13  12  11  10   9   8   7   6   5   4   3   2   1  /
 \                                                    / 
  \  25  24  23  22  21  20  19  18  17  16  15  14  /  
So it's also the Pin layout on the solder side of the Male DB-25 Cable Connector that plugs into it

Pins 18,19,20,21,22,23,24 and 25 are all ground pins and you may either use all or any one of them.

These datapins are TTL logic output pins (0 low, +5v high).

      D(n) Out ------+
  Port         Opto input HVPS-PRO
        Ground ------+
HVPS-PRO uses TTL negative logic. When the data pin is set to logic high (1), the hv output is turned off, and when the data pin is set to logic low (0), the hv output is turned on. Disconnecting the parallel port plug, will thus return the unit to normal 'on' operation.

To know the base address of your parallel port from Windows, right click on My computer, select Properties, Device Manager, Ports (Com & LPT), LPT1, Properties, Resources. Alternatively you can get the information from DOS using:

   -d 0040:08 L8
   0040:0008 78 03 78 02 00 00 00 00
   In this exampe 0378 is the address.

Controlling the printer port using various languages

The following examples are short code examples to control your power supply using different languages. Up to 8 power units can be controlled with your parallel port. I/O address 378h is the normal address for printer port 1.


MOV DX,0378H
Where n is the data you want to output.


OUT &H378, N

Where N is the number you want to output.
suppose you control your power supply using Data bit 1, you would connect the opto isolated input to parallel port pin 2 (+) and 18(-). To turn off the HV output you type:

OUT &H378, 1

to turn on the hv output, you type: OUT &H378, 0


Where N is the data you want to output.

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