Practical flyback tarfo power source for prototyping various HV devices, considering that it can work continuously for a long time without heating up, it does not require much knowledge to make it, and its cost is very low.
A high voltage power supply is an electronic device that provides an electrical output at high voltages, typically ranging from hundreds of volts to several kilovolts (kV), or tens kilovolts. Very often, DIYers need such a device to perform various experiments, prototyping circuits and tests. Generally, this type of device requires a powerful low-voltage DC source, and then a DC to AC circuit with powerful MOSFETs, which is relatively complex to build, and also expensive.
Specifically in this case I will explain to you a much simpler way to make such a device. The positive sides of this design are first of all the simplicity, then the low price, which avoids the use of expensive semiconductor elements, and also one of the most important features, which is the possibility of longer-term operation. Of course, this less outdated design also has negative features, primarily the offline mode of operation, which means that the city voltage network is used directly, as well as the low oscillator frequency, which is limited to a few kilohertz due to the semiconductors used, and thus the coefficient of useful action when transforming the voltage is reduced.
The device consists of several components:
- Two MKP capacitors with a value of 4µF to 8µF/400V (I use four parallel-connected capacitors of 1µF each for 4µF total)
- one capacitor 100nF/400V
- diode bridge (Graetz)
- diode 1N4007 2 pcs
- Flyback trafo from old TV or CRT monitor
- Potentiometer 500 Kohms
- Thyristor of the BT151 type or similar
- and few resistors
I also put an automatic fuse is placed at the input of the circuit, which should turn off the power in the event of a circuit error or burnout of any of the components.
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Let's explain the principle of operation. At the beginning, at the input of the circuit we have a switch and a circuit breaker. Then comes a series-connected MKP capacitor in this case with a value of 4µF. This capacitor limits the current in the circuit and if we double its value, the current will also double, but in this practical case its value should not exceed 8µF. For the sake of safety during long-term uninterrupted operation, I chose this lower value. Then comes a diode bridge- rectifier whose output is connected to a capacitor of 8µF. Next is the Triggering Stage for BT151Thyristor. A voltage divider using 220k + 220k in parallel with a 500k potentiometer is used to control the gate of the thyristor. A 10k resistor goes to each side of the SCR gate from the voltage divider output, along with a 10nF capacitor and diode protection. And the flyback (HV Trafo) is driven through 10 turns on the primary.
With the potentiometer, we bring a certain gate current to turn on, and at that moment the thyristor conducts and discharges the capacitor through the primary winding of the flyback transformer. Then there is a pause until the capacitor is recharged, and this process repeats.In this circuit configuration, changing the potentiometer setting changes the thyristor's firing threshold relative to the capacitor voltage. When the thyristor fires at a lower capacitor voltage, the firing frequency increases, but the output voltage decreases. In this way, we can roughly regulate the value of the high output voltage, which is a particularly useful option for experimentation.
I should also mention that the primary winding of the high-voltage transformer usually consists of about 10 turns of insulated copper wire with a cross-section of at least 1mm.
Now let's see how the device works in real conditions. First, the potentiometer should be in the far left position. We turn on the device and gradually move the potentiometer until a spark appears between the electrodes at the output of the flyback transformer.
Now the frequency is the lowest, and the voltage is the highest, and the spark has the greatest length. With further movement of the potentiometer, the frequency increases, but the voltage decreases. I will repeat this with several different flyback transformers.
And finally, a brief conclusion. Although it is made with somewhat outdated technology, this device has excellent positive characteristics when it comes to using it in laboratory conditions for prototyping various devices, considering that it can work continuously for a long time without heating up, it does not require much knowledge to make it, and its cost is very low.
SAFETY NOTE: Please do not attempt to recreate the experiments shown on this video unless you are familiar with High Voltage Safety Techniques! Direct Current even above 60V maybe lethal, even when the AC supply voltage has been disconnected due to the stored energy in the capacitors. I have no responsibility on any hazards caused by the circuit. Be very careful. This is a humble request.
