AN2503

PDP Power Devices characteristics

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Figure 22.

Circuit scheme – set and reset

4

PDP Power Devices characteristics

A clear idea of circuit operation will help us to highlight the main features of the devices

involved. In particular the analysis can be split in power devices analysis and driving devices

analysis, in order to address specific characteristics of each device.

4.1

Power devices from ST

Power devices in PDP have common characteristics that range from high peak current

capability and low forward voltage drop to fast turn-ON capability. The current both in the

Energy Recovery Circuit (ERC) and in the Discharge Circuit (DC) follows a half sinusoidal

pattern. ERC and DC could be simply classified as soft switching converters. In fact, the

circuit can be considered as a series resonant LCR circuit, so the current at turn-ON is zero

(zero current switching) and the voltage at turn-OFF is zero (zero voltage switching).

Since a MOSFET has an intrinsic body diode across it, a MOSFET does not require an anti-

parallel diode when selected as power devices on the discharge circuit, while an IGBT

needs a specific freewheeling diode. For ER circuit, the Power Switch does not require an

anti-parallel diode since reverse current is blocked by the diodes in series with the devices

(D1, D3, D5 and D7), thus MOSFET or IGBT can be used as power devices on the ER

circuit.

Diodes D2, D4, D6 and D8 provide additional protection clamping the voltage on the

inductors avoiding damage to devices on the ER circuit.

Path circuit has to carry both ER and Discharge currents, thus it is required to have very low

voltage drop. It can be noted that during ER and Discharge cycles, the pass circuit remains

on. The Path circuit switches on and off only during reset period which happens at the end

of each subfield, which means that the maximum frequency is in the range of 1 kHz. The

Path circuit is a bidirectional circuit, so a MOSFET, that can carry current in both directions,

could be used for this circuit.

ST has a broad range of products covering the power section ranging from MOSFET and

IGBT to dedicated Diodes.

Vs

Vs

Vs

Vset

L7

T9

T10

T8

T12

T11

-Vres

et

Cp

CS1

CS2

L1

D7

D8

D6

D5

T7

D1

Vs

T3

T2

T1

T4

T6

T5

D2

D4

D3