Request: Variable high voltage DC source.

[lightt]

Hi,
I know we are talking mostly about electronic specified projects here (mostly microcontroller based) but I need a good power source schematic for testing purpose.

Ok, I can try to define the details of circuit I am looking.
I need high voltage variable DC source, it means the output voltage can be vary between 0 and 1000 volts DC and output current must be 5 mA or more at full output voltage.  Accuracy is very important, for example I should be set the output voltage to 487 V, and during this period I should be read the current. Measuring systems isn't important because I already have accurate and calibrated equipments. 
I found some circuits using Fly-back transformer but mostly their output range so high (mostly not variable) and the output has not pure DC. (the ripple factor of output must be loweror equal than 0.01 % because for 1000 V DC 1% ripple factor equal 20 V peak to peak AC signal on my test object and it is not permissible

By the way any other helpful ideas are welcome such as commercial products (must be purchased in Turkey)
Thanks for your help.

[picavr]

you can use the coil ignition (car motor) methode ,itv s more simple

[dideco]

You can use a camera flash circuit to have about 400V. You can adjust the input voltage, so the output voltage. But 400V will not fit to your test equipment, so you can use 3 circuits in series and reach up to about 1200 Volts DC easily. Probably you need to use isolated power supplies for each circuit because most of the transformers used in camera flash circuit has some pins connected to power supply ground.

You can also use some switchs to sellect 0 to 400V, 400 to 800 and 800 to 1200 Volts etc.

Easiest way to find camera flash circuit is buying three cameras which use films and can only be used one time for developing. Or, you can ask the used and thrown cameras from photography shop.

I think this is the fastest and the cheapest way of getting about 1200 Volts etc. But I am not sure about the currents that could be drawn from the circuits.

[lightt]

Hi,
Thanks guys, I will remember your advice. I going to find a car ignition coil and a flash circuit. I will check the limitations of the circuits.

[MAXPAYNE]

Hope it will help u......

http://rapidshare.com/files/137766259/A_Kilowatt_Switching_High_Voltage_Power_Supply.rar.html

[omni]

Here's a link I found useful regarding ignition coil HV power source:

http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm

[TomJackson69]

Here's a link I found useful regarding ignition coil HV power source:

http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm

Hello Lightt,

The easy way, if you can find a high voltage step-up transformer. Jameco sell VARIAC input 125Volts, output 0-135Volts and current upto 2.5Amps for about $45 USD. You will need a step-up transformer, input 115Volts, output upto what you need; in this case, 1000Volts. The variac will vary the output from 0 to 115Volts (or 135Volts depend on how you connect the output), it than connect to the step-up transformer.

By using full bridge rectifier, current limit resistor, electrolictic cap and current sensing resistor, you have a variable high voltage power supply. Put fuse on the input and also one fuse for the output.

For ripple filter, use formular from any instroduction to electronic text book or search from the internet.

For measurement, I don't think you would have any problem because you said you already have calibrated equipments.

I used to order transformer from Pacific Transformer (in USA), they can wind a transformer for you by your spec. The price of your transformer I don't know, but, for the one I order with this spec, input 115Volts, output 750Volt at 350mA, dual secondary (you get 1500Volts when you connect in series), it costs $90 USD. This is an example of how I buy the transformer, your country must have something similar.

If you already have low voltage transformer, you may want to use diode rectifier connect with capacitor as voltage multiplier; how many stage is depend on the input and output. But the current is low (due to the small capacitor), but, you only need mA anyway.

Other member (PICAVR) suggested to use car ignition coil. I think it is good too. I don't remember what is the output of that coil, but it's very high (something like 600Volts). You will need pulse generator for input to the ignition coil to get the output voltage.

Good luck,

Tom

[dideco]

Dear friends,

"TomJackson69" suggested a Variac transformer and a step up transformer to reach 1000 Volts DC. It is OK. But, I think, one point is missing: Mains power usually fluctuates in seconds, it is not constant. By using a step up transformer, this fluctiation would be much greater at the secondary coils.

We must find another solution...

[lightt]

Hi,

Firstly I special thanks to all of you.

TomJacson69 you are right and I already built one of them approximately 1 years ago. It is very useful and handy products but its testing performance is poor, because of variac mechanical working principles. when adjusting variac some peaks occure on voltage and the test object faild due to the these unwanted peaks. (test object fails because it has varistor and other surge protection compenents) By the way I used my variac based source for testing of high voltage varistors.
So that dc-dc converter is better choice for my application
Actually I didn't remember any practical approaches to dc-dc converters, because there was a long time to my graduate from university.

Thanks again guys.

[TomJackson69]

Hi,

Firstly I special thanks to all of you.

TomJacson69 you are right and I already built one of them approximately 1 years ago. It is very useful and handy products but its testing performance is poor, because of variac mechanical working principles. when adjusting variac some peaks occure on voltage and the test object faild due to the these unwanted peaks. (test object fails because it has varistor and other surge protection compenents) By the way I used my variac based source for testing of high voltage varistors.
So that dc-dc converter is better choice for my application
Actually I didn't remember any practical approaches to dc-dc converters, because there was a long time to my graduate from university.

Thanks again guys.

Hi Lightt,

I found this project may be of your interest:

Copy from the web site:
"The basic circuit described in this document is capable of generating up to 30 kilovolts or more from a low voltage DC source using the flyback (LOPT) transformer salvaged from a B/W or color TV or computer monitor. Typical output with a 12 VDC 2 A power supply or battery will be 12,000 V. Maximum output current at full voltage is typically around 1 to 2 mA. Higher currents are available but the output voltage will drop. At 2 KV, more than 10 mA may be possible depending on your particular flyback transformer input voltage and current.
As you can see from the schematic below, it doesn't get much simpler than this!


   +Vcc     Q1   +----------------+ |:|
                o           |                 )|:|
               |       B |/ C                )|:|
          |  +------|    2N3055         )|:|
              |  |      |\ E           5 T  )|:| +------|>|----------o  +HV
                |  |        |                 )|:|(   HV Diode, usually
               |  |       -_-                )|:|(    built in.
                 |  |                          )|:|(
     +--|-------------------------+ |:|(
              |  |   Q2  _-_                )|:|(
                 |  |        |                 )|:|( Secondary (HV) winding,
              |  |    B |/ E           5 T  )|:|(  intact.
           |  |  ----|    2N3055         )|:|(
               |  |  |   |\ C                )|:|(
                |  |  |     |                 )|:|(
        |  |  |     +----------------+ |:|(
                |  |  |                        |:|(
      |  |  -----------------------+ |:| +------------------o  -HV
               |  |                     2 T  )|:|
            |  |               +---------+ |:|
               |  |               |     2 T  )|:| T1 - Flyback transformer from B/W or
      |  +-------------------------+ |:|      color TV or computer monitor.
      |                  |
      |            R1    |    R2
     +----------/\/\/\--+--/\/\/\--+
                  110        27   _|_
                  5 W        5 W   -


This design is derived from a circuit found in: "Build your own working Fiberoptic, Infrared, and Laser Space-Age Projects", Robert E. Iannini, TAB books, 1987, ISBN 0-8306-2724-3. "

Here is the link:
http://members.misty.com/don/hvinvert.htm

You will need to work on the controlling circuit to make it variable power supply. Sometime ago, I have a schematic of high voltage power supply from SORENSON with both voltage-control and current control. I will try to locate this schematic, if I find, I will post a copy here.

The web site above is well worth to take a look.

Good luck,

Tom

[Walkura]

Maybe its a stupid idea but you don't need big currents so maybe its usefull.
Attached i have the setup i use to place n-mosfets on the highside of the load .
Normaly i use this to create ~12 volt above source level so i can use nmos (low-rds) on the high side (that way i cam measure the exact power on the load)
But what i was thinking you can feed this with a regulated powersupply .
Also instead of the small bc transistors you can use bd's or bigger & upscale the capacitor .
For every stage you put in serie you will double the voltage (minus 2 diode drops)
Every stage to higher voltage you could devide the capacitor value by 2 (afterall your current will be half of the previous stage .)
Your ripple will double with every stage .
But when you build a nice regulated supply with lets say a lm723 to power it ,you several times doubled ripple will still be small .
Also you could make a output on every stage so you don't have to use the highest stage with lower voltage testing .
I didn't calculate my way through it ,so i might have proposed something silly .
But for my gatedriving i use 10 uF ,2,2 works too but showed a little drop (i used 900 Ohm bleeder resistors to minus to close my fet).
From old tv's i know you have good 1 or 2,2 or even 4,7 uF capacitors in 800 or 1000 Volt .
For those few milli amperes it might be enough

[elcielo]

http://www.ahv.com/

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