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SP4403 데이터시트(PDF) 6 Page - Sipex Corporation |
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SP4403 데이터시트(HTML) 6 Page - Sipex Corporation |
6 / 14 page SP4403DS/05 SP4403 Electroluminescent Lamp Driver © Copyright 2000 Sipex Corporation 6 The Switched H-Bridge Network The H-bridge consists of two SCR structures that act as high voltage switches. These two switches control the polarity of how the lamp is charged. The SCR switches are controlled by the f LAMP signal which is the oscillator frequency divided by 128. For a 50kHz oscillator, the 7 flip flops will drive f LAMP= 390Hz. When the energy from the coil is released, a high voltage spike is created triggering the SCR switches. The direction of current flow is determined by which SCR is enabled. One full cycle of the H-bridge will create 128 voltage steps from ground to 80V (typical) on EL1 and EL2 (pins 4 and 5, respectively) which are 180 degrees out of phase from each other (see Figure 5). A differential representation of the output is shown in Figure 6. Fine Tuning Performance Circuit performance of the SP4403 can be improved with some of the following suggestions: Increase EL Lamp Light Output: By connecting a fast recovery diode from COIL (pin 3) to C INT (pin 7), the internal diode of the switched H-bridge network is bypassed resulting in an increase in light output at the EL lamp. We suggest a fast recovery diode, such as the industry standard 1N4148, be used for D1. This circuit connection can be found in Figure 2. Square Wave Output Waveform to the EL Lamp: A 470pF capacitor at C INT (pin13) will act as an integrating capacitor, filtering out any coil switching spikes or ripple in the output waveform to the EL lamp (shown if Figure 1). A designer may change the output waveform to a square wave by using a 0.1 µFcapacitor(shown in Figure 2) at C INT (pin 13). Printed Circuit Board Layout Suggestions: The SP4403's high-frequency operation makes PC layout important for minimizing ground bounce and noise. Keep the IC's GND pin and the ground leads of C1 and C INT in Figure 2 less than 0.2in (5mm) apart. Also keep the connections to L1 (pin 3) as short as possible. To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the IC's V SS (pin 2) directly to the ground plane. EL Lamp Driver Design Challenges There are many variables which can be optimized for specific applications. The amount of light emitted is a function of the voltage applied to the lamp, the frequency at which it is applied, the lamp material, the lamp size, and the inductor used. Sipex supplies characterization charts to aid the designer in selecting the optimum circuit configuration (see Figures 7 to 14). Sipex will perform customer application evaluations, using the customer's actual EL lamp to determine the optimum operating conditions for specific applications. For customers considering an EL backlighting solution for the first time, Sipex is able to offer retrofitted solutions to the customer's existing LED or non-backlit product for a thorough electrical and cosmetic evaluation. Please contact your local Sales Representative for Sipex or the Sipex factory directly to initiate this valued service. |
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