<30 V MOSFETs
Active load circuit in DC/DC
conversion
Description
This circuit provides a simple and cost effective
alternative to ‘off-the-shelf’ electronic load circuits and is
ideal for carrying out efficiency testing of low- to
medium-power DC/DC converters. A single 1A load
section is formed around SW1a, R2a, R3a, C3a, C4a, IC2a
and Q1a and multiple 1A load sections may be connected
in parallel to achieve a complete circuit capable of sinking
in excess of 10A. Switchable in steps of 1A via SW1, the
overall current may also be fine tuned by adjusting VR1.
Benefits
• Simple design and extremely cost effective
• Little drift over time compared to ordinary resistive
loads
• Low power consumption - can be battery powered
thereby providing a true ‘floating’ load
Suitable Products
• PHP78NQ03LT (Q1a)
• LM358N (IC2)
<30 V MOSFETs
PDA Backlight Supply
<30 V MOSFETs
Buck conversion for high-end
graphics cards (VGA)
<30 V MOSFETs
Power switching in CCFL resonant
inverters
Description
Dual N-channel MOSFETs can be used as power switches
inside resonant inverters for the high voltage power
supply of Cold Cathode Fluorescent Lamps (CCFL) in
LCD backlighting applications. In the application circuit
below a full bridge converts the low DC voltage (typically
3 V to 28 V) to an AC voltage.The IC controls the four
N-channel MOSFETs to produce a low AC voltage that is
transformed to a higher AC voltage, which in turn powers
the CCFL tubes.
The drain-source voltage of the MOSFET must be
selected to withstand the maximum voltage that can
occur on the DC input.The MOSFETs recommended in
the table below are suitable for lamp powers ranging
from 1 W to about 5 W. For half or full bridge
configurations either single or dual MOSFETs can be
used. Note that the total power capability of two single
TSOP6 packages is equal to one SO8 package or twice
the power capability of a TSSOP8 package.
Benefits
• Lower R
DS(on)
than P-channel MOSFETs
• Latest Trench technology helps improve system
efficiency
- lower on-state resistance
- increased inverter efficiency
• High integration, reduced component count
Suitable Products
Power MOSFETs
• PHKD6NO2LT
• PHN203
• PHKD13NO13LT
• PHKD3NQ10T
• PMWD16UN
• PMWD19UN
• PMWD30UN
• PMGD370XN
• PMN45EN
• PMN40LN
• PMN23UN
Driver IC
• UBA2070
Description
The following circuit is ideal for providing a white LED
backlighting supply in, for example, cellular phones and
PDAs that are powered from a single battery cell. Q1, Q2
and associated components form a simple oscillator
running at approximately 25 kHz. Due to the very low
threshold characteristics of Q1 and Q2, this oscillator will
function with a supply voltage of 1.2 V or less. Q3, L1 and
the LED(s) are configured as a non-isolated flyback
converter.The ‘flyback’ action of L1 provides sufficient
voltage to drive the LED(s), whose forward voltage is
typically 3 to 4 V per device.The circuit may also be
configured to run at increased supply voltages e.g. for a
3 V supply and 3 LEDs, change R2 to 560
and L1 to
560 µH.
Benefits
• Will power a single, dual or triple LED in series with the
circuit values shown
• Operation with supply voltage
1.2 V – which can be
extended to higher voltages
• Uses readily available components
Suitable Products
• Philips Si2302DS (Q1, 2, 3)
Description
Modern high-end graphics cards typically incorporate
their own fast, dedicated graphics processor (GPU) and a
large amount of memory. The power consumption of
such graphics cards is now similar to that of complete
motherboards from two to three years ago, with the
GPU alone requiring up to 10A at an approximate voltage
of 1.7 V. The GPU supply is usually derived from a higher
voltage (3.3 V in this case) via a synchronous buck
DC/DC converter. Correct choice of power MOSFETs in
the DC/DC converter is essential if the converter is to
run with acceptable temperature and efficiency.The Philips
PHK12NQ03LT and PHK28NQ03LT MOSFETs are ideal
for this application, and are available in the industry
standard SO8 package, prevalent in this application.
Benefits
• Efficiency equal to leading industry requirements
• Very low R
DS(on)
specification and fast switching enables
lower working temperatures
• Lower profile to simplify compact design
Suitable Products
• PHK12NQ03LT
• PHK28NQ03LT
PHK12NQ03LT
PHK28NQ03LT
R
DS(on)
mΩ
14
10.5
7.5
7.1
@V
GS
V
4.5
10
4.5
10
Circuit Diagram
Circuit Diagram
Circuit Diagram
V
CC
V
IN
= 3.3 V
Circuit Diagram
Vdc
to additional
load sections
12 V
IC1
I
Q1a
PHP87NQ03LT
(on heatsink)
C3a
10
µF
(16 V)
R2a
10 kΩ
IN
R1
100
Q1, Q2, Q3:
Philips Si2302DS
R4
100
C2
4.7
µF
L1
330
µH
Q1
LED
1.5 V
(nominal)
Controller
CCFL
78L05
C
O
R4
4.7
kΩ
SW1a
0V
to additional
load sections
C4a
47 nF
R3a
1
(10 W)
to DC-DC
converter
R3
1 kΩ
R2
C1
10 nF
Q2
Q3
PWM
CONTROLLER
V
OUT
= 1.7 V at
10A "V
CORE
"
C2
C1
1
µF
1
µF
(35 V) (35 V)
VR1
2 kΩ
(10 T)
IC2a
1/2LM358N
Q1
OUT
bra541
7.5 kΩ
0V
bra532
Q2
0V
bra534
50
51
Home Index Pages Text
Previous Next
Pages: Home Index