Versatile energy recovery circuit for driving AC plasma display panel with single sustain circuit board

Abstract

This paper presents an energy recovery (ER) circuit which can operate either in a series or a parallel resonance mode and can drive an AC plasma display panel (PDP) with a single sustain circuit board. The proposed ER circuit consists of one energy storage capacitor, two energy recovery inductors, and three insulated-gate bipolar transistors. The circuit operations in the series and parallel resonance modes are similar to conventional ones, except for the leading edge of the first sustain pulse and the trailing edge of the last sustain pulse. To reduce power consumption in the parallel resonance mode of operation, these two pulse edges are generated using a series resonance between the panel capacitance and the energy recovery inductor. The proposed circuit had energy recovery efficiencies in both the series and parallel resonance modes that were nearly the same as the efficiency of the conventional series resonance ER circuit. Experimental results on a 42-inch XGA single-scan PDP show that the proposed ER circuit is suitable for use in a PDP drive circuit.

Introduction

The power consumption of an AC plasma display panel (AC PDP) occurs mostly in the sustain discharges. The major current supplied to the PDP for sustain discharge is a displacement current because two sustain electrodes, the scan (S) and common (C) electrodes, are separated from the discharge gap by an insulator. Accordingly, the PDP has been modeled with a capacitor C_p to analyze behavior of sustain drive circuits [1], [2]. The simplest full-bridge type of sustain drive circuit is shown in Fig. 1 [3]. It consists of four MOSFET switches only, and its operation consists of three switching states: the SUS_UP_S, SUS_DN, and SUS_UP_C states. The SUS_UP_S and SUS_UP_C states generate the sustain pulses for S and C, respectively. When the circuit is driven at a voltage of V_sus, each sustain pulse charges up the panel with an energy of $C_{\text{p}}{V}_{\text{sus}}^2/2$. The same amount of energy is dissipated in the circuit to charge the panel. At the SUS_DN state, the stored energy is dumped to the ground and the voltages of S and C return to 0 V. Accordingly, the amount of energy dissipated for each pulse is $C_{\text{p}}{V}_{\text{sus}}^2$. If the number of sustain pulses per second is f, the power consumption is $C_{\text{p}}{V}_{\text{sus}}^{2}f$, which becomes intolerable for a practical AC PDP. Furthermore, high charging and discharging currents cause electromagnetic interference (EMI) and circuit heating problems. To relieve these problems, an energy recovery (ER) circuit has been added to the full-bridge sustain circuit.

To recover the energy stored in the panel, all existing ER circuits use either a series or parallel resonance between the panel capacitance C_p and an energy recovery inductor. Two typical circuit configurations of the ER circuit are shown in Fig. 2, Fig. 3. The series resonance ER circuit shown in Fig. 2 was invented by Weber and adopted by many PDP manufacturers [4], [5]. It uses two separate ER circuits for S and C. The energy storage capacitors C_ss and C_cs are charged initially to a voltage of V_sus/2. Sustain pulses are generated using seven switching states: the ER_UP_S, SUS_UP_S, ER_DN_S, ER_UP_C, SUS_UP_C, ER_DN_C, and SUS_DN states. The initial state is the SUS_DN state at which the voltages V_c of the C electrode and V_s of the S electrode are at 0 V. The switch S2 remains closed to keep V_c = 0 V, while generating a sustain pulse for S. At the ER_UP_S state, the inductor L_s and the panel capacitor C_p form a series resonance circuit and the energy stored in C_ss are supplied to C_p. The voltage V_s of the S electrode reaches V_sus at one half of the resonance period. The SUS_UP_S state starting at t = t₁ holds V_s at V_sus. At the ER_DN_S state starting at t = t₂, L_s and C_p forms a series resonance circuit and V_s decreases to 0 V at one half of the resonance period. The energy stored in C_p is recovered to the energy storage capacitor C_ss. After all stored energy is recovered, the SUS_DN state starts to hold V_s at 0 V. The subsequent sustain pulse for C is generated using the ER_UP_C, SUS_UP_C, ER_DN_C, and SUS_DN switching states on the energy recovery circuit for C, which operates in the same way as the circuit for S. The circuit shown in Fig. 2 has the advantage of flexible sustain waveform design at the expense of cost because it uses two separate ER circuits.

The parallel resonance ER circuit shown in Fig. 3 was invented by Sakai [6], [7]. This circuit uses a parallel LC resonance between C_p and L. The sustain pulses are generated using the SUS_DN, SUS_UP_S, TRANS_A, SUS_UP_C, and TRANS_B states. At the SUS_DN state, both V_s and V_c are at 0 V. The SUS_UP_S state sets V_s = V_sus and V_c = 0 V. The first sustain pulse for S is generated using the SUS_UP_S state starting at t = t₀. Next, the TRANS_A state starting at t = t₁ forms a parallel resonance circuit consisting of C_p and L, and V_s decreases to 0 V at one half of the resonance period, while V_c increases to V_sus. The SUS_UP_C state begins at t = t₂ after V_c reaches V_sus and maintains the voltages V_c = V_sus and V_s = 0 V. At t = t₃, the TRANS_B state starts and V_c decreases to 0 V, while V_s increases to V_sus. The sequence of SUS_UP_S, TRANS_A, SUS_UP_C, and TRANS_B is repeated until the last sustain pulse. The last sustain pulse is generated using a sequence of TRANS_A, SUS_UP_C, and SUS_DN states. When compared with the ER circuit shown in Fig. 2, the number of circuit elements required in this circuit is significantly reduced. However, because the energy stored in one electrode is being used to charge up the other, the transitions of voltages for S and C occur simultaneously and it is impossible to adjust the separation between the sustain pulses. Also, a hard switching is unavoidable for the first and last sustain pulses, resulting in an EMI problem and an increase in power dissipation.

The challenging factors in designing the ER circuit have been a reduction of circuit cost and an increase of power efficiency, while increasing the degree of freedom in tuning the sustain waveform. This paper proposes an energy recovery circuit which can recover energy from both the S and C electrodes using a single sustain circuit board. The proposed circuit has high power efficiency and good flexibility in tuning the sustain waveform. The operational principle of the proposed circuit is given in Section 2 and experimental results are given in Section 3. A conclusion is given in Section 4.