DPA-Switch™ DC-DC Forward
Converter Design Guide
Application Note AN-31
•
•
Selectable 300 kHz or 400 kHz operation
Lossless integrated cycle-by-cycle current limit
Introduction
The single-ended forward converter topology is usually the
best solution for DC-DC applications in industrial controls,
Telecom central office equipment, digital feature phones, and
systems that use distributed power architectures.
The example circuits in this design guide illustrate the use of
these and other features of DPA-Switch.
Scope
The feature set of DPA-Switch offers the following advantages
in DC-DC single-ended forward converter designs:
This document gives guidance for the design of a single-
ended forward converter with DPA-Switch in applications
that require a single output voltage. It is intended for systems
engineers and circuit designers who wish to become familiar
with the capabilities and requirements of DPA-Switch in
DC-DCapplications.Thisapplicationnoteprovidesbackground
materialthatwillassistusersoftheDPA-SwitchDC-DCforward
converter design utility that is included in the software design
tool, PI Expert. Subsequent application notes will provide
comprehensive procedures for designs of greater complexity.
Designers are advised to check Power Integrationsʼwebsite at
www.powerint.com for the latest application information and
design tools.
•
•
Low component count
High efficiency (typically >91% with synchronous
rectification)
•
•
•
•
•
•
•
Built in soft-start to minimize stress and overshoot
Built in accurate line under-voltage detection
Built-in accurate line overvoltage shutdown protection
Built in adjustable current limit
Built-in overload and open loop fault protection
Built-in thermal shutdown
Programmable duty cycle reduction to limit duty cycle
excursion at high line and transient load conditions
Very good light-load efficiency
•
Snubber
Output
Inductor
Power
Transformer
+
+
Bias
Voltage
Output
Capacitor
CCLAMP
VO
+
–
RUVLO
DC
INPUT
TL431 with
Frequency
Drain
Clamp
Compensation
DPA-Switch
D
S
L
U1
CONTROL
FEEDBACK CIRCUIT
C
CBYPASS
F
RFC
CFC
Input
Return
PI-2873-062204
Figure 1. Typical Configuration of DPA-Swtich in a Single-Ended DC-DC Forward Converter with One Output.
July 2004