HV9906X データシートの表示（PDF） - Supertex Inc
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HV9906X Datasheet PDF : 10 Pages
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Design Information - continued
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.
DN3145N8
HV9906
Vs
1 +Vin
GATE 8
2 Von
PGND 7
3 Vdd
NS 6
4 AGND
PS 5
This method limits the +VIN voltage to VDD + VGS(OFF) of the
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. The worst-case power
dissipation in the HV9906 is now given by the equation
Power Dissipation HV9906 = (VDD + VGS(OFF)max ) × IIN
and the dissipation in the depletion MOSFET is given by the
equation
Power Dissipation in MOSFET ≈ (VS − VDD − VGS(OFF) ) × IIN
Which for the previously calculated input current of 3mA, 265VRMS
input voltage and using the DN3145N8 depletion MOSFET yields
the following results.
Power Dissipation HV9906 = (11+ 3.5) × 3 × 10−3 = 43.5mW
Power Dissipation in MOSFET ≈ (265 − 10 − 1.5) × 3 ×10−3
Power Dissipation in MOSFET ≈ 0.76W
HV9906
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 θca
=
Tj
− Ta
− (Rθjc × VIN(max)
VIN(max) × IIN
× IIN )
Rθca is the required thermal resistance of the encapsulating
material.
Tj is the maximum junction temperature.
Ta is the maximum ambient temperature.
Rθjc is the junction to case thermal resistance of the package.
VIN(max) is the maximum DC or RMS input voltage.
IIN is the input current required at the highest operating frequency.
As an example, consider an application where the input current is
3mA as calculated earlier, operating with a maximum input voltage
of 265VRMS in an 85°C ambient and an SOIC packaged device will
be used. The thermal resistance of the encapsulating material can
then be calculated as follows.
R θca
=
150
− 85 − (45 × 265 × 3 × 10−3 )
265 × 3 × 10−3
=
36.76°C /
W
High Thermal Conductivity Encapsulant
R θca
R θjc
Dice
Printed Circuit Board
8
07/23/02
Supertex, Inc. 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 FAX: (408) 222-4895 www.supertex.com
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