DAK-86 Power Integrations, DAK-86 Datasheet - Page 14

• Manufacturer Part Number: DAK-86
• Description: KIT REF DES DPA 6.6W DC-DC CONV
• Manufacturer: Power Integrations
• Series: DPA-Switch®r

Specifications of DAK-86

• Main Purpose: Special Purpose DC/DC, Power Over Ethernet
• Outputs And Type: 1, Isolated
• Power - Output: 6.6W
• Voltage - Output: 3.3V
• Current - Output: 2A
• Voltage - Input: 33 ~ 57V
• Regulator Topology: Flyback
• Frequency - Switching: 400kHz
• Board Type: Fully Populated
• Utilized Ic / Part: DPA423, DPA424, DPA425
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Other names: 596-1195

Rev. S 12/07
Application Examples
Figure 25. A High Effi ciency 30 W, 5 V, Telecom Input DC-DC Converter.
High Effi ciency 30 W Forward Converter
The circuit shown in Figure 25 is a typical implementation of a
single output DC-DC converter using DPA-Switch in a forward
confi guration with synchronous rectifi cation. This design
delivers 30 W at 5 V, from a 36 VDC to 75 VDC input with a
nominal effi ciency at 48 VDC of 90% using the DPA425R.
By taking advantage of many of the built-in features of the
DPA-Switch, the design is greatly simplifi ed compared to a
discrete implementation. Resistor R1 programs the input under-
voltage and overvoltage thresholds to typically 33 V and 86 V
respectively. This resistor also linearly reduces the maximum
duty from the internal maximum of 75% at 36 V to 42% at
72 V to prevent core saturation during load transients at high
input voltages. The DPA-Switch internal thresholds are
toleranced and characterized so the designer can guarantee
the converter will begin operation at 36 V, necessary to meet
ETSI standards, without the cost of an external reference IC.
The current limit is externally set by resistor R3 to just above the
drain current level needed for maximum load regulation to limit
the maximum overload power of the converter. The externally
programmable current limit feature also allows a larger
DPA-Switch family member to be selected. Using the X pin, the
current limit can be adjusted to the same level. A large device
reduces conduction losses and improves effi ciency without
requiring any other circuit changes. This has been used here to
replace the DPA424R with a DPA425R.
36-75 VDC
14
+
V
V
IN
IN
*Optional components
C1, C2 & C3
DPA422-426
2.5 A
1 μH
100 V
1 μF
L1
SMBJ
VR1
150
D
619 kΩ
S
1%
R1
CONTROL
CONTROL
X
18.2 kΩ
L
1%
R3
F
C
DPA-Switch
U1
DPA425R
1.5 kV
1 nF
220 nF
C7
T1
C5
10 Ω
R17
10 Ω
R15
Si4888
10 Ω
R14
Q2
DY
C9*
68 μF
1.0 Ω
10 V
C6
R4
3300 pF
10 kΩ
R16
C17
D4
BAV19WS
R5*
The selectable 300/400 kHz switching frequency is set to
300 kHz by connecting the FREQUENCY (F) pin to CONTROL (C).
DRAIN voltage clamping is provided by VR1, which keeps the
peak DRAIN voltage within acceptable limits. Transformer core
reset is provided by the gate capacitance of Q1 with R17 in
series. Optional reset capacitance C9 with R5 can be added if
necessary to supplement the gate capacitance of Q1.
The output of the transformer is rectifi ed using MOSFETs to
provide synchronous rectifi cation. The UV/OV function, together
with the turns ratio of the transformer, defi nes the maximum
MOSFET gate voltage, allowing the very simple gate drive
arrangement, without the need for drive windings or a drive IC.
During primary on-time, capacitor C17 couples charge through
resistor R15 to drive the gate of the forward MOSFET, Q2.
Capacitor C17 provides a DC isolated drive for Q2, preventing
gate overstress on Q1 during power down. The time constant
formed by R16 and C17 is selected to be much longer than one
switching cycle. Diode D4 resets the voltage on capacitor C17
before the next switching cycle. During the primary off-time, the
diode D2 provides a conduction path for the energy in inductor
L2 while Q1 is still off. The transformer reset voltage on the
secondary winding directly drives a positive voltage on the gate
of catch MOSFET, Q1. MOSFET Q1 provides a low loss
conduction path for a substantial portion of the primary off-time.
An isolated auxiliary winding on L2, rectifi ed and fi ltered by D1
and C4, provides the bias supply for the optocoupler transistor.
Si4888
PC357N1T
DY
Q1
D2
U2
4.7 μF
20 V
C4
19WS
BAV
D1
L2
10 kΩ
10 μF
BAV19WS
LM431AIM3
10 V
R7
C13
D3
U3
150 Ω
U2
R6
100 μF
10 V
C10
100 μF
10 V
C11
100 nF
5.1 Ω
R12
C16
1 μF
C14
10 V
1 μF
C12
10.0 kΩ
10.0 kΩ
220 Ω
R10
R11
1%
1%
R9
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PI-3472-061704
5 V, 6 A
RTN