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TitleTesla Transformer for Experimentation and Research
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Page 48

High-frequency converter POWER SUPPLY DESIGN

34 Marco Denicolai

The theoretical power achieved with these components is:

( )



1 =





P (5-12)

The calculated power capacity is more than sufficient to ensure an actual value surely
greater than the targeted 1.25 kW.

5.2.2. Bridge switch design

The bridge switch module includes four IGBT solid-state switches, their drive circuitry plus
additional components generating 560 V, 15 V and 5 V DC.

The IGBT is a relatively new power semiconductor device, which provides the best
features of both the MOSFET and the BJT [Tak95]. Among its advantages:

• Low-power, voltage-driven gate turn-on and turn-off. Gate impedance as high as a

• Low conduction losses.
• Positive temperature coefficient. The device will not experience thermal run-away

typical of BJTs.

• Possibility to use either integrated or external anti-parallel diode.
The traditional disadvantage of the IGBT is its slow turn-off speed that results in the well-

known current tail. For this application, as the SLR converter commutations take place
always when the load current is zero, the slow turn-off doesn’t represent a problem. The
IGBT used is the IRG4PH40UD type, which features an integrated anti-parallel diode with a
relatively fast and soft reverse recovery characteristic The manufacturer recommends it for
hard-switching operation up to 40 kHz, but for resonant-mode operation guarantees 200 kHz

Table 1: Absolute maximum ratings for the IRG4PH40UD device

Parameter Value

Collector-to-Emitter breakdown voltage 1200 V

Continuous collector current 30 A

Pulsed collector current 120 A

Diode continuous forward current 8 A

Diode maximum forward current 130 A

Even if the commutations take place at zero current, unwanted spikes and noise in general
are present in many nodes of the schematics, due to:

• Parasitic capacities Cce, Cgc and Cge internal to the IGBTs.
• PCB traces impedance.
• Reverse recovery time of the anti-parallel diodes.
• Electromagnetic radiation and coupling within the converter PCB.
The most significant source of unwanted noise is, anyway, the Tesla transformer itself.

When the spark gap conducts and the charged capacitor is quickly discharged on the primary

Page 96


82 Marco Denicolai

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