Royer Flyback driver


SPECIFICATIONS

Input voltage range: 10 - 40 Volts DC , 5-10 Amps (50-400Watts)

Output voltage range: 10.000-30.000 Volts DC (depends upon the frequency and the transformer used)

Estimated Open circuit voltageOutput voltage: 13.000 - 14.000 Volts DC (300 Mohm ± 3 Mohm voltage divider) with 24V input

Efficiency: 40-60% (depends on components value, see description for details)

Estimated efficiency: 50%, during arcing (300 Mohm ± 3 Mohm voltage divider) with 24V input

PART LIST

Part simbol
Part Name
Quantity
----
10-40V 5-10V Power supply
1
FU1
16A Automotive fuse
1
----
10A Switch
1
R1
1KOhm 1/4W resistor
1
D1
Red Led (5mm)
1
L1
47-200uH Ferrite bobbin inductor (can be hand wound)
1
R4,R5
470Ohms 2W resistor
2
R2,R3
10KOhms 2W resistor
2
D2,D3
12V 1W zener diode
2
D7,D8
MUR240 2A 400V Ultrafast diode (or equivalent)
2
Q1,Q2
FDH44N50 SPMS Series FailchildSemiconductor Power Mosfet 44A, 500V, 120mOhms
2
C1
0.68-1uF 250VAC rated polyester cap
1
T1
Diode split monitor High Voltage Flyback Transformer
1

 

SCHEMATIC

Description

This circuit is an auto-oscillating, resonant, current fed High voltage DC-DC converter. The output voltage is calculated as follows Vout = Vin * pi * Nsecondary / Nprimary. The primary peak voltage is Vin * pi , and the rms voltage is Vin*pi*0.7 . Keep in mind that unless you have a true-rms multimeter or your circuit is well tuned (primary waveform = sinewave) you will read wrong values. The mosfet must be rated more than pi times the input voltage, preferably 4 or 5 times the Vin. The primary waveform is a sinewave in ideal conditions or a squarewave if the storing inductor (L1) is not big enough. The squarewave produces more switching losses and spikes in the mosfets, so an eccessive mosfet heating is an indicator that the circuit is not properly tuned. Under correct operation the mosfet heating must be almost absent. The L1 inductor, if properly sized, ensures the waveform to be a sinewave, reduce voltage stress on switches, and so increase efficiency. It also has current limiting purposes and stores the energy for the next cicle. If too big will reduce the power consumption of the circuit and the output. Esperiment for the best performance/efficiency. The resonant frequency is determined by the primary inductance and the cap capacitance f=1/(2*pi*SQRT((L1+L2)*C)). Choose the cap value for the best performance. The cap type must be rated for 250VAC and with low RF dissipation factor. This circuit has the best cost/complexity - efficiency/power ratio. This type of circuit can drive also air cored resonant transformers (yes, tesla coils), or DC-DC conversion transformers to get higher voltage or higher current and finally it works well also for RF induction heating. The versatility is extreme but proper component values, in particular the resonalt cap and the inductor, are essential. Don't bolt the two heatsinks toghether or you will short the cap!. Also remember that there is Vin*pi*0.7 Volts rms between them (in my case with 24V i read 50Vac rms) that can result in a light (or stronger) shock and rf burns, so dont touch them and encase the project in a box if you can.

Difficulty/Cost: 45% (MEDIUM)

Danger::: 70% HIGH + 10%

This circuit is highly dangerous. The output current is enough to cause cardiac fibrillation in some cases and severe burns. If used to charge high voltage caps it becomes lethal. This thing can source as much power as you can provide until the transformer or the resonant capacitor fails. At max power these circuits can power medium sized tesla coils and lasers. Remember that 30mA are enough to stop your heart. Make sure the insulations are in good state and in no cases you should come close to the output with bare hands. Arm to arm shock is potentially lethal. Light shock and RF burn hazard on the primary side on the transformer, see above for details.

Video Gallery

MiniMOT-style Arcs videos, showing a steel needle melting.

Video 1 (4.6 Mb) - Download

Video 2 (7.8 Mb) - Download

Image Gallery

Enjoy the image gallery, showing the MOT-style arcs produced by the device. Some camera flooding happened due to the strong Blackbody IR radiation emitted from the melted iron needle used as a discharge electrode. The circuit is very efficient and produces little heat even in long operatons , and discharges (short circuits). Notice that the transformer primary wires are too thin, they do not have an optimal resistance, also skin effect further increases resistance (we are working at 30KHz in my case).

 

The driver circuit itself

Pics of the transformer and the driver

mini-MOT-style arc pictures

Other arc pictures

Camera Flooding due to excessive IR

The circuit and the high voltage flyback transformer fitted into a computer psu case. The fan is for heatsing cooling purposes (12V fan with a LM317 regulator to stabilize and step down the voltage)

A led shows the status of the supply to avoid touching the output while active

Arcing photos (a 24V 6A power supply is on the back)

More arcing photos