D372A Datasheet, PDF (3/12 Pages) List of Unclassifed Manufacturers – Electroluminescent Lamp Driver IC

Block Diagram of the Driver Circuitry
VBAT
E
V+
L+
L
CHF
High
Frequency
Oscillator
o
g
i
c
CLF
Low
Frequency
Oscillator
Divide
by 2
CS
L
o
g
i
c
Rd
GND
EL1
EL2
EL Lamp
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.
The D372 chip inverter drives the EL lamp by using a switching BJT to repeatedly charge an external inductor and
discharge it to the high voltage capacitor Cs. The discharging causes the voltage at Cs to continually increase. When
the voltage at Cs reaches a nominal value, the switching BJT is turned off. The internal circuitry uses the H-bridge
technology, using both electrodes to drive the EL lamp. One of the outputs, EL1 or EL2, is used to discharge Cs into the
EL lamp during the first half of the low frequency (LF) cycle. By alternating the state of the H-bridge, the other output
is used to charge the EL lamp during the second half of the LF cycle. The alternating states make it possible to achieve
200V peak-to-peak across the EL lamp.
The EL driving system is divided into several parts: on-chip logic control, on-chip high voltage output circuitry, on-chip
discharge logic circuitry, and off-chip components. The on-chip logic controls the lamp operating frequency (LF) and
the inductor switching frequency (HF). These signals are used to drive the high voltage output circuitry (H-bridge) by
delivering the power from the inductor to the lamp. The integrated discharge logic circuitry uses a patented wave
shaping technique for reducing audible noise from an EL lamp. Changing the Rd value changes the slope of the linear
discharge as well as the shape of the waveform. The off-chip component selection provides a degree of flexibility to
accommodate various lamp sizes, system voltages, and brightness levels.
Typical D372 EL driving configurations for driving EL lamps in various applications are shown on the following page.
The expected system outputs for the various circuit configurations are also shown with each respective figure. These
examples are only guides for configuring the driver. Durel provides a D372 Designer^’s Kit, which includes a printed
circuit evaluation board intended to aid you in developing an EL lamp driver configuration using the D372 that meets
your requirements. A section on designing with the D372 is included in this datasheet to serve as a guide to help you
select the appropriate external components to complete your D372 EL driver system.
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