D355B Datasheet, PDF (3/14 Pages) List of Unclassifed Manufacturers – Electroluminescent Lamp Driver IC

Block Diagram of the Driver Circuitry
E’
1.0 µF
V+
L+
CLF1
CLF2
Low
Frequency
Oscillator
High
Frequency
Oscillator
VOUT
EL Lamp
L-
GND
Theory of Operation
Electroluminescent (EL) lamps are essentially capacitors with one transparent electrode and a special phosphor
material in the dielectric. When a strong AC voltage is applied across the EL lamp electrodes, the phosphor
glows. The required AC voltage is typically not present in most systems and must be generated from a low
voltage DC source. Thus, Durel developed its patented Three-Port (3P) switch-mode inverter circuit to
convert the available DC supply to an optimal drive signal for high brightness and low-noise EL lamp
applications. The Durel 3P topology offers the simplicity of a single DC input, single AC output, and a
shared common ground that provides an integrated EMI shielding.
The D355B drives the EL lamp by repeatedly pumping charge through an external inductor with current
from a DC source and discharging into the capacitance of the EL lamp load. With each high frequency (HF)
cycle the voltage on the lamp is increased. At a period specified by the lamp frequency (LF) oscillator, the
voltage on the lamp is discharged to ground and the polarity of the inductive charging is reversed. By this
means, an alternating positive and negative voltage is developed at the single output lead of the device to one
of the electrodes of the EL lamp. The other lamp electrode is commonly connected to a ground plane, which
can then be considered as electrical shielding for any underlying circuitry on the application.
The EL driving system is divided into several parts: on-chip logic and control, on-chip high voltage output
circuitry, discharge logic circuitry, and off-chip components. The on-chip logic controls the output frequency
(LF), as well as the inductor switching frequency (HF), and HF and LF duty cycles. These signals are
combined and buffered to regulate the high voltage output circuitry. The output circuitry handles the power
through the inductor and delivers the high voltage to the lamp. The selection of off-chip components provides
a degree of flexibility to accommodate various lamp sizes, system voltages, and brightness levels. Since a
key objective for EL driver systems is to save space and cost, required off-chip components were kept to a
minimum.
Durel provides a D355B Designer’s Kit, which includes a printed circuit evaluation board intended to aid
you in developing an EL lamp driver configuration using the D355B that meets your requirements. A section
on designing with the D355B is included in this datasheet to serve as a guide to help you select the appropriate
external components to complete your D355B EL driver system.
Typical D355B configurations for driving EL lamps in various applications are shown on the following
page. The expected system outputs, such as lamp luminance, lamp output frequency and voltage and average
supply current draw, for the various sample configurations are also shown with each respective figure.
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