HV9925SG-G Supertex, HV9925SG-G Datasheet - Page 6

• Manufacturer Part Number: HV9925SG-G
• Description: LED Drivers Programmable Current LED Lamp
• Manufacturer: Supertex

Specifications of HV9925SG-G

• Operating Supply Voltage: 20 V to 400 V
• Maximum Supply Current: 500 uA
• Maximum Power Dissipation: 800 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC N EP
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In order to avoid false triggering of the current sense
comparator, C
following expression:
where T
V
The typical DRAIN and R
in Fig. 3 and Fig. 4.
Estimating Power Loss
Discharging the parasitic capacitance C
output of the HV9925 is responsible for the bulk of the
switching power loss. It can be estimated using the following
equation:
where F
DRAIN current of the HV9925. The switching loss is the
greatest at the maximum input voltage.
Disregarding the voltage drop at HV9925 and D1, the
switching frequency is given by the following:
When the HV9925 LED driver is powered from the full-wave
rectified AC input, the switching power loss can be estimated
as:
V
The switching power loss associated with turn-off transitions
of the DRAIN output can be disregarded. Due to the large
amount of parasitic capacitance connected to this switching
node, the turn-off transition occurs essentially at zero-
voltage.
When the HV9925 LED driver is powered from DC input
voltages, conduction power loss can be calculated as:
P
where D = V
I
F
DD
AC
IN(MAX)
COND
S
is the internal linear regulator current.
=
is the input AC line voltage.
V
= (D • I
V
is the maximum instantaneous input voltage.
IN
IN
BLANK(MIN)
S
• T
- V
is the switching frequency and I
OFF
O
O
O
/V
2
P
• R
IN
must be minimized in accordance with the
is the minimum blanking time of 200ns, and
ON
is the duty ratio, R
) + I
DD
SENSE
• V
IN
voltage waveforms are shown
• (1 - D)
●
ON
1235 Bordeaux Drive, Sunnyvale, CA 94089
is the ON resistance,
SAT
P
into the DRAIN
is the saturated
(9)
(5)
(6)
(7)
(8)
6
When the LED driver is powered from the full-wave
rectified AC line input, the exact equation for calculating the
conduction loss is more cumbersome. However, it can be
estimated using the following equation:
where V
and K
D
Figure 1. Conduction Loss Coefficients K
EMI Filter
As with all off-line converters, selecting an input filter is critical
to obtaining good EMI. A switching side capacitor, albeit of
small value, is necessary in order to ensure low impedance
to the high frequency switching currents of the converter. As
a rule of thumb, this capacitor should be approximately 0.1-
0.2 µF/W of LED output power. A recommended input filter is
shown in Figure 2 for the following design example.
Design Example 1
Let us design an HV9925 LED lamp driver meeting the
following specifications:
Input:
Output Current: 20mA
Load:
The schematic diagram of the LED driver is shown in
Figure 2.
P
m
COND
=0.71Vo/(V
K
K
D
C
(
(
D
D
M
= (K
M
d
)
)
AC
can be determined from the minimum duty ratio
0.7
0.6
0.5
0.4
0.3
0.2
0.1
C
●
is the input AC line voltage. The coefficients K
0
• I
Tel: [phone]
AC
O
2
).
0.1
Universal AC, 85-264VAC
String of 10 LED (LW541C by OSRAM
V
• R
F
= 4.1V max. each)
ON
0.2
) + (K
0.3
D
●
• I
D
www.supertex.com
DD
M
0.4
• V
AC
0.5
)
C
and K
0.6
HV9925
0.7
d
(10)
C