The Variable High Voltage Power Supply 0-300V

Here is the variable high voltage dc power supply circuit, which we can customize the output voltage from 0 to 311Vdc, and it is protected the current over the limit that we define at about 100 mA.

You may like these
LM338 5A Variable regulator Better life with high current in same voltage 1.25V to 30V.

In the circuit, you can see the T1 is a mains transformer with a ratio of 1:1, for security reasons, and reduces noise signal as well.

The Variable High Voltage Power Supply 0-300V

Then the mains voltage from the T1 is rectified to DCvolt with bridge diode D1-D4, We use a No. 1N4007 that withstand voltage as 1,000V at the current 1A and this DCV is filtered through the capacitor C1 – 220uF 400V be the big size electrolytic types, by the voltage drop across C1 is about 311VDC.

The power MOSFET Q1 has controlled the current output, by using the resistor R3 – 500K adjust the voltage gate pin of Q1.


The ZENER diode ZD1-12V is available to prevent overvoltage at gate pin of the Q2 if we does not have it when high volt the Q2 may be damaged.

The transistor Q2-BC337 and the shunt resistor R2 – 3.3ohm are added as a current limiter. When the current output is too increased, the Q2 will stop the gate pin of the Q1 immediately, which will be guarding the higher current output. The degree of R3 gets from testing in this circuit, which depending on the gain of the transistor or the hFE value, so you may need to tune the value of R2

Note: The Q1 should hold a big size heatsink, it will have power around 311V x 100mA = 31 watts You can use the power MOSFET Q1 has several numbers that be N-channel, Enhancement mode, Vds=400V, Id=10.5A such as: IRF740, BUZ326 etc.
The output impedance of the power supply is defined by the beta degree of the Q1, thus the impedance of large MOSFET lower than the output impedance.

This circuit works well as Video below:


Additionally, you can see the high-voltage power circuit other. below…

  1. 3 High Volts power supply circuits ideas
  2. 12V to 300V DC-DC converter circuit

Get Ebook: Simple Electronics Vol-03

Get Updates via Email

We always try to make Electronics Learning Easy.

36 thoughts on “The Variable High Voltage Power Supply 0-300V”

  1. I would like to know what is the wattage of the resistors, and in particular how many watts should be 3.3 ohms R2.
    Thank you. Toni Hypnos.

    Vorrei sapere qual è la potenza in watt delle resistenze e in particolare di quanti watt deve essere la R2 da 3,3 Ohm.
    Grazie. Toni Ipnos.

  2. Hi guys,

    I am currently working on this schematic in eagle. I’ve worked out everything so far, until I ran into the trafo. I would like to know what kind of trafo it is.

  3. Thank you for giving a sign of life, but do not tell me what power in WATTS should be the resistance of 3.3 ohms.

    Grazie per aver dato un segno di vita, ma non mi dite di quale potere in WATT dovrebbe essere la resistenza da 3,3 ohm.

  4. If you cannot figure out the resistor’s power rating and which transformer you need for this circuit, it might not be a good idea for you to build this circuit 🙂

  5. The specification of all the parts are in the text, or can be easily calculated from the circuit.
    This power supply could kill you, if you don’t understand what you are using and take adequate precautions.

  6. hi
    i want use this “variable high voltage power supply 0-300V” for PWM motor ,but my motor have 3.5 AMP and 180 DC,pleas help me


  7. the use of a N-Channel MOSFET as a a high-side power switch (i.e., drain tied to V+ and the source feeding the circuit and subsequently the load beyond that), the FET will not turn completely ‘on’ by simply bringing the gate voltage up to V+. You will need to bring the gate voltage ABOVE the rail voltage to get the FET to turn completely on. which simply means that circuit will never conduct the full current its capable off; i would be greatly interested in just how much current this circuit could supply..

    i myself am looking at 500ma, so if anybody has built this circuit i would like to know, both does its 0 – 300v capabilities actually work, and if changing the 3.3 ohm resistor actually alter ma output.

  8. I’m curious. Assuming the zener is indestructible and its purpose is to keep the base voltage of Q2 12V, wouldn’t it restrict the output to 12V max, no matter where VR1 is set?

  9. The video is belong to my experiment, I have slightly modified the circuit to maintenance 300VDC, I add a 100K resistor in between B+ and 500K , and i add a 24V x 12 = 294V zener parrallel with 500K.

    I didn’t use MOSFET because i don’t have on hand i ‘m using FGA25N120ANTD 1200V 25A IGBT , i think any MOSFET will work as long as the Vds can withstand 400V and above.

    I’m Using the transformer is design for valve/tube amplifier, having output 230V and 6.3V, the 6.3V winding i use to power the digital voltmeter for voltage and current as well.. the current actually is 1V meter with 1 ohm resistor in low side sense as shunt.

    Good luck

  10. Hi, I’m an amateur with little knowledge in electronics. I need to electrolytic experiments, a power supply that has high voltage like yours, but the current must be adjustable up to a maximum of 25 or better 20 milliamperes. Where and how should I act on your plan to get what I need? Advance infinite thanks.
    Toni Ipnos.

  11. I am trying to use this circuit to control a sewing machine for better low speed control. Being in the US, it wants to run on 110VAC.

    It works very well but the current limit does not seem to work. I need about 500mA so a 1 ohm resistor should be about right but it makes no difference what the value is. I get full power out even using a 10 Ohm resistor.

    I am using a 2N3904 NPN if that makes any difference.

    Any ideas?

    Marengo, Illinois

  12. Hi Toni Ipnos,
    Thanks for your feed.
    Since I have very little time. Each day, the work website is only 2 hours.
    Some circuits, I have not tried to create their own. It is not clear.
    I am sorry.

  13. Si los elementos de la figura los selecciono para que permitan circular mayor corriente, ¿podria tener la misma fuente de 0 a 300 V con corrientes muy superiores a 300 mA.
    If the elements of the selected figure to allow higher current round, could have the same source of 0-300 V with much higher than 300 mA current.

  14. Hi..

    Regarding the current sense NPN transistor Q2:
    When it will turn on has nothing to do with hFE, but the base-emitter on-voltage, seen in the datasheet it is 1,2v for this NPN transistor.
    1,2v / 3,3 Ohm = 363 mA
    363mA x 1,2v = 436 mW

    To get 500mA the value of R2 have to be
    Using the 2n3904 / BC547 NPN transistor with a base-emitter on-voltage at 0,7v will do a difference.
    If still keeping the 3,3 Ohm R2 resistor then:
    0,7v / 3,3 Ohm = 212 mA
    212mA x 0,7v = 148 mW

    For 500mA output:
    With BC337 transistor = 1,2v / 500mA = 2,4 Ohm
    1,2v x 500mA = 0,6 mW

    With 2N3904 / BC547 transistor = 0,7v / 500mA = 1,4 Ohm
    0,7v x 500mA = 0,35 mW

    So clearly it is best to use a Q2 transistor with low on-voltage to avoid high wattage on the R2 resistor.

    Regarding the 12v zener, which function as a limiter to avoid the gate voltage across the mosfet (Gate-Source) voltage to be higher than 12v, it could actually be a 16v / 18v zener, because most mosfets has a max gate-source rating at 20v.

    Yeah.. sorry that was a lot..
    And of course.. remember a fuse at the ‘hot terminal’ before the 1:1 transformer…..!!!

  15. I need 300V DC regulated power supply. Please let me know how to do that. Also let me know how can I eliminate the ripple in the circuit.

  16. hellow sir good evening
    my quetion is i m repairer of electronics instrument like lcd led tv and other dental and medical instrument.
    i have one smps for lcd funai tv.using ic M2303ADN 3.3v dc out put @3.5 amp right now ic not available so any idea for equilent no for this.
    please aknowledge.thanks and regards.
    have a nice day.
    subhash padhiyar.

  17. Hi
    I have make one. It worked very well. The voltage output and over current protector are well too.
    But i wonder why maximum current is 100mA only. Can we make it bigger?

  18. Hi,
    I have make one, and it worked very well, but it is possible to increase the current output to 2A, 3A or higher, to replace the component T1 1:1 by 5A, Diode Bridge 6A, and then Q2 by 2N3055 ? please, i appreciate any reply or suggestions, thank you.

  19. i have put this together with if840 as 740 not available to me i used a 220 to 220 tranformer from a shaver socket even though i have 280vdc at drain of mosfet with pot full on it only gives me 110 at its output any idea why ?

  20. Looks like is no working.
    According the ngspice simulation the mosfet gate is always around 4.5 volts. It does not mater if the potentiometer is 1% 50% 100%.

  21. Also manage 200volts with a manual potentiometer is at least risky.
    I believe that manual potentiometer must be below 20 volts to reduce the electrical shock.

    • Hello francisco javier,
      I am very grateful. Your information is very useful for us and everyone. You are kind and take the time to explain to us.
      Thank you very much.

  22. This configuration works better in simulation but still I have hight voltage in R2 (pontentiometer).
    that is because we need differential voltage from gate to source in fet. So every time that increase the source voltage you need increase the gate voltage.
    So maybe is a good idea send the source to ground. and connecting the load R1 to the drain terminal. So the voltage is regulated by load and the mosfet. Also mosfet do not have good linear zone to control . So I am going try with bipolar or igbt .


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.