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A Digitally Controlled
Isolated Power Converter
Introduction
Digital power conversion has been identified
as
a
practical
approach
to
the
implementation of Switched Mode Power
Converters. To reduce the size of passive
components, high switching frequencies of
100KHz–1MHz are utilised. The design of
digital compensators and Digital Pulse Width
Modulation (DPWM) circuitry to support
such switching frequencies is possible in
modern CMOS processes. The digital
SMPC approach may also be successfully
extended to isolated power converters. This
invention describes an enhanced bidirectional digital communication scheme for
use in isolated AC-DC and DC-DC SMPC
digital power converters.
Technology
In order to achieve reliable transfer of serial
data across the isolation barrier a robust
communication protocol is required. For use
within a power conversion application
several specialised requirements must be
met. Firstly the communication protocol data
rate must be fast enough to transfer the
error voltage data corresponding to the
current switching period. Secondly sufficient
time must be allowed to calculate the duty
cycle for the next switching period. Figure 1
details the use of the technology within an
isolated power converter. The technology
enables the use of primary side control of
the power converter. Secondly serial digital
transmission of the digitised analogue error
signal avoids opto-coupler aging issues.
ADC data
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Programmable
Reference
Voltage
Clock
Reference
Value
ADC
ADC data
Clock
Auxiliary
signals


The
bi-directional
communications
scheme has been implemented on
FPGA technology and demonstrated
within a digitally controlled isolated
power converter.
Commercial Opportunity
The University of Limerick is interested in
seeking partners to exploit the commercial
potential of these technologies by entering
into licensing agreements and/or innovation
partnerships that mutually benefit both
parties. It is envisaged that this technology
would be of interest to companies engaged
in power converters, embedded power
conversion design or mixed-signal IP.
IP Status
COM Primary Side
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Clock
COM Secondary Side
Auxiliary
signals
Loop Controller (DSP with
DPWM)
Reference
Value

SMPS
Secondary Side
Barrier
Isolation
SMPS
Primary Side

output. The start of the received
data package triggers the ADC
sampling process.
The secondary side uses the
encoded
data
to
adjust
a
programmable reference voltage to
produce the selected output voltage.
Clock recovery on secondary side
allows synchronisation of primary
and secondary side.
The communications system may
be
used
with
any
coupler
technology.
Additionally both sides can send
auxiliary data to the opposite side.
This data is appended to the main
data. This auxiliary data may include
safety signals like over-voltageprotection (OVP), over-temperatureprotection (OTP) and power failure
(PF) but also arbitrary end-user data
The invention is the subject of a patent
application that is currently undergoing
examination
Figure 1: Isolated power Converter with Bi-drectional
Communications system
The novel features of this approach are:

The primary side controller can
determine instant when the ADC
samples the secondary side voltage.
This allows sampling of a settled
Contact
Dr. Tony Scanlon
Dept of Electronic Eng.
University of Limerick
Limerick
Ireland
t: +353-(0)61-203343
e: [email protected]
John Gleeson
Technical Transfer Office
University of Limerick
Limerick
Ireland
+353-(0)61-234683
e: [email protected]