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SP4425Q

Electroluminescent Lamp Driver for Low Noise Applications

Signal Processing Technologies 

The following scope photos show the affect the tuning resistors (QR1 and QR2) have on the output

waveform. Figure 11 implements only 5KΩ of series resistance introducing only a slight amount of

filtering of the discharge edge. Figure 12 shows that if the values are increased to 10KΩ the discharge

edge is reduced even further. A 20KΩ example is shown in Figure 14 and represents the most amount

of filtering needed. Again, the balance in light output and audible noise must be observed for each

application.

VBATTERY

Coil=Toko 1.2mH/19Ohm

VDD

CINT=1800pF

COSC=270pF

SP4425Q

QR1=5K-20KΩ

QR2=5K-20KΩ

EL Lamp

Figure 11.

QR1=QR2=5KΩ

VPP=196VPK-PK, FLAMP=269Hz

Low noise suppression level

Figure 12.

QR1=QR2=10KΩ

VPP=187VPK-PK, FLAMP=268Hz

Low noise suppression level

Figure 13.

QR1=QR2=15KΩ

VPP=177VPK-PK, FLAMP=269Hz

High noise suppression level

Figure 14.

QR1=QR2=20KΩ

VPP=168VPK-PK, FLAMP=266Hz

High noise suppression level

SP4425QDS/12

SP4425Q Electroluminescent Lamp Driver

9

© Copyright 1998 Sipex Corporation

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