D340B Datasheet, PDF (4/9 Pages) List of Unclassifed Manufacturers – Electroluminescent Lamp Driver IC

Block Diagram of the Driver Circuitry
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 D340B 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. When the voltage on the lamp reaches the set voltage on the comparator, 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, and
off-chip components. The on-chip logic controls the inductor switching frequency (HF) and change in lamp charging
polarity at a frequency (LF) that is dependent on the lamp load size and DC voltage source. 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 D340B Designer’s Kit, which includes a printed circuit evaluation board intended to aid you in
developing an EL lamp driver configuration using the D340B that meets your requirements. A section on designing
with the D340B is included in this datasheet to serve as a guide to help you select the appropriate external components
to complete your D340B EL driver system.
Typical D340B 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.
4