HV9921N3-G Supertex, HV9921N3-G Datasheet - Page 5

• Manufacturer Part Number: HV9921N3-G
• Description: LED Drivers Switchmode PWM
• Manufacturer: Supertex

Specifications of HV9921N3-G

• Operating Supply Voltage: 85 V to 264 V
• Maximum Supply Current: 350 uA
• Maximum Power Dissipation: 740 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• Package / Case: TO-92
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

When the switching MOSFET turns on, the capacitance C
is discharged into the DRAIN pin of the IC. The discharge
current is limited to about 150mA typically. However, it
may become lower at increased junction temperature. The
duration of the leading edge current spike can be estimated
as:
In order to avoid false triggering of the current sense
comparator, C
following expression:
where T
V
Estimating Power Loss
Discharging the parasitic capacitance C
the HV9921 is responsible for the bulk of the switching power
loss. It can be estimated using the following equation:
where F
DRAIN current of the HV9921. The switching loss is the
greatest at the maximum input voltage.
The switching frequency is given by the following:
F
where
When the HV9921 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 pin 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.
C
P
P
T
S
AC
IN(MAX)
SWITCH
SWITCH
SPIKE
P
= (V
is the input AC line voltage.
<
= ((V
I
η
is the maximum instantaneous input voltage.
IN
SAT
BLANK(MIN)
=
≈
is the efficiency of the power converter.
- η
S



2 T
⋅
is the switching frequency, I
IN
-1
V C
(
⋅
T
• V
• C
IN
V
1
P
BLANK MIN
OFF
2
2
IN MAX
must be minimized in accordance with the
is the minimum blanking time of 200ns, and
O
P
) / V
) / (I
(
P
(
(
V
+
SAT
IN
AC
)
V I
• T
IN SAT
)) +t
)
⋅
−
C
OFF
t
P
rr
rr
+ ⋅
)
⋅
2 I
t
rr



●
SAT
⋅
F
1235 Bordeaux Drive, Sunnyvale, CA 94089
S
P
⋅
into the DRAIN pin of
t
SAT
rr
)
is the saturated
(
V
AC
(4)
(5)
(6)
(7)
(8)
−
η
−
1
⋅
V
O
P
)
5
Conduction power loss in the HV9921 can be calculated as:
P
where D = V
I
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:
P
where V
and K
the HV9921.
Fig. 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
Let us design an HV9921 LED lamp driver meeting the
following specifications:
Input:
Output Current: 20mA
Load:
DD
COND
COND
is the internal linear regulator current.
Kd Dm
Kc Dm
= (D • I
= (K
d
(
(
can be determined from the minimum duty ratio of
AC
)
)
C
●
0.7
0.6
0.5
0.4
0.3
0.2
0.1
is the input AC line voltage. The coefficients K
• I
O
Tel: [phone]
O
0
/ηV
O
2
2
• R
• R
Universal AC, 85-264VAC
String of 10 LED (LW541C by OSRAM
V
IN
F
0.1
ON
= 4.1V max. each)
ON
is the duty ratio, R
) + (I
) + (K
0.2
DD
D
• V
• I
●
0.3
DD
IN
www.supertex.com
Dm
• (1 - D))
• V
0.4
AC
ON
)
C
is the on-resistance,
and K
0.5
HV9921
d
0.6
(9)
(10)
0.7
C