HV9906 Supertex Inc, HV9906 Datasheet - Page 8

• Manufacturer Part Number: HV9906
• Description: Simple Off-Line/PFC & >9V DC/DC Switcher
• Manufacturer: Supertex Inc

Design Information -
Operating from a full wave rectified AC input
For these applications there is no minimum input voltage, thus
adding a fixed value series resistor is not possible. However, a
dynamic resistor consisting of a depletion MOSFET may be added
as depicted in the following diagram.
This method limits the +V
depletion MOSFET for all input voltages and in fact raises the
maximum allowable peak input voltage to the breakdown voltage
rating of the depletion MOSFET.
dissipation in the HV9906 is now given by the equation
Power Dissipation HV9906 = (
and the dissipation in the depletion MOSFET is given by the
equation
Power Dissipation in MOSFET
Which for the previously calculated input current of 3mA, 265V
input voltage and using the DN3145N8 depletion MOSFET yields
the following results.
Power Dissipation HV9906 = (
Power Dissipation in MOSFET
Power Dissipation in MOSFET
Vs
DN3145N8
Supertex, Inc. 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: [phone] FAX: [phone] www.supertex.com
1
2
3
4
+Vin
Von
Vdd
AGND
HV9906
IN
PGND
11
GATE
V
DD
voltage to V
NS
PS
0.76W
(
(
continued
. 3
265
V
S
V
) 5
8
7
6
5
GS
V
(
OFF
3
10
DD
The worst-case power
)
10
max
. 1
V
DD
) 5
)
GS
3
(
+ V
I
OFF
IN
43
3
)
5 .
)
GS(OFF)
10
mW
I
IN
3
of the
RMS
8
Using High Thermal Conductivity Encapsulation
For an encapsulated application the required thermal resistance of
the encapsulating material can be calculated using the following
equation.
R
material.
T
T
R
V
I
As an example, consider an application where the input current is
3mA as calculated earlier, operating with a maximum input voltage
of 265V
be used. The thermal resistance of the encapsulating material can
then be calculated as follows.
R
IN
j
a
IN(max)
is the maximum junction temperature.
ca
jc
is the input current required at the highest operating frequency.
is the maximum ambient temperature.
ca
is the junction to case thermal resistance of the package.
is the required thermal resistance of the encapsulating
is the maximum DC or RMS input voltage.
150
RMS
High Thermal Conductivity Encapsulant
R
Printed Circuit Board
in an 85 C ambient and an SOIC packaged device will
ca
85
265
T
(
45
j
3
T
a
265
10
V
R (
IN
3
(max)
3
jc
10
V
R
R
IN
I
IN
ca
jc
(max)
3
)
36
I
IN
.
76
)
Dice
C
/
W
HV9906
07/23/02