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dc2393af
DEMO MANUAL DC2393A
DESCRIPTION
LT8304
Micropower No-Opto Isolated
Flyback Converter with 150V/2A Switch
Demonstration circuit 2393A is a micropower no-opto
isolated flyback converter featuring the LT
®
8304. This
demo circuit outputs 5.0V, and maintains tight regula-
tion with a load current from 20mA up to 4.2A and over
an input voltage from 18V to 72V. The output current
capability increases with the input voltage, as shown in
the Performance Summary table.
The DC2393A needs less than 0.5% of its full output power
as a minimum load to maintain good output voltage regu-
lation. On the DC2393A, in order to avoid pre-loading, a
5.6V Zener diode is placed between its V
OUT
+
and V
OUT
–
to
serve as a minimum load.
Transformer leakage inductance causes a voltage spike
on the primary side after the power switch turns off. To
limit this leakage inductance spike within MOSFET volt-
age rating of 150V, an RC snubber and a TVS clamp are
installed to damp the ringing and clamp the MOSFET drain
voltage to a safe level.
The Performance Summary table summarizes the perfor-
mance of the demo board at room temperature. The demo
circuit can be easily modified for different applications with
some pre-designed transformers.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
PERFORMANCE SUMMARY
The LT8304 is a simple to use monolithic micropower
isolated flyback converter. By sampling the isolated output
voltage directly from the primary-side flyback waveform,
the part requires no third winding or opto-isolator for
regulation. The output voltage is programmed with two
external resistors and a third optional temperature compen-
sation resistor. By integrating the loop compensation and
soft-start inside, the part reduces the number of external
components. Boundary mode operation provides a small
magnetic solution with excellent load regulation. Low
ripple Burst Mode
®
operation maintains high efficiency
at light load while minimizing the output voltage ripple. A
2A, 150V DMOS power switch is integrated along with all
the high voltage circuitry and control logic into a thermally
enhanced 8-lead SO package.
The LT8304 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 2393A
Design files for this circuit board are available at
http://www.linear.com/demo/DC2393A
Specifications are at T
A
= 25°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage 18 48 72 V
Output Voltage V
IN
= 18V – 72V
I
OUT
= 20mA – 2A
4.75 5 5.25 V
Maximum Output Current V
IN
= 18V 2 A
V
IN
= 24V 2.4 A
V
IN
= 48V 3.5 A
V
IN
= 72V 4.2 A
Output Voltage Ripple (Peak–to–Peak) V
IN
= 48V, I
OUT
= 3.5A 100 mV
Minimum Switching Frequency I
OUT
= 0mA 11 kHz
Efficiency V
IN
= 24V, I
OUT
= 2.4A 83 %
V
IN
= 48V, I
OUT
= 3.5A 84 %
