Advancing the
Power Curve
®
Page 1 www.synqor.com | QMS#065-0000053 | Rev. D | 09/22/21 | Advancing the Power Curve®
Paralleling Capability of
SynQor® Converters and
Power Supplies
Application Note
Introduction
Many SynQor
®
power converters have built-in paralleling capability. This functionality allows increased total
load power and often redundancy with the addition of output OR’ing FETs or diodes. The table that follows on
pages 4-8 provides a summary of whether paralleling is built into the design for a given converter family. It also
includes some additional information about how the converter design implements the current sharing feature.
For converters that do not have built-in paralleling capability, the table indicates whether they may be made to
operate in parallel with the addition of an external current-sharing circuit that makes adjustment to the converter’s
output voltage Remote-Sense or Trim inputs.
Contents
Types of Current-Share Methods ..........................................................................2
Analog Method: ......................................................................................2
Digital Method: ......................................................................................2
Droop Method: .......................................................................................2
External Analog Current Sharing: .......................................................................3
Quick Reference Guide to Paralleling Capabilities of SynQor Products ........................................4-8
– PowerQor, DualQor, BusQor, NiQor, iQor, ATCA .................................................................4
– InQor, InQor DC Filters, RailQor, CFQor, ACuQor, PFCQor, PFICQor, AC Filters .......................................5
– Hi-Rel Single Output, Hi-Rel Dual Output, Hi-Rel BusQor, Hi-Rel DC Filters .........................................6
– MilQor MCOTS, MCOTS BusQor, MCOTS Non-Isolated ..........................................................7
– MPFCQor, MPFICQor, MCOTS DC Filter, MCOTS AC Filter, AeroQor AC Filter, AeroQor PFIC ...........................8
SynQor Power Supplies: .................................................................................9
– MultiQor, VPX ...........................................................................................9
Summary
This application note provides an overview of the paralleling
capabilities of the different SynQor power converter families.
Application Note Paralleling Capability of SynQor Converters and Power Supplies
Advancing the
Power Curve
®
Page 2 www.synqor.com | QMS#065-0000053 | Rev. D | 09/22/21 | Advancing the Power Curve®
Types of Current-Share Methods
Different current-share methods are implemented in SynQor converters and power supplies. These include the
analog method, digital method and droop method. Following is a brief description of each method.
Analog Method:
Converters using an analog current-share method have a “share” control bus with a voltage that represents
the average load current per paralleled converter connected. With this current-share method, all the converters
operate without any single converter being in overall control, i.e., there is no master. An advantage of analog
current-sharing is that an individual converter in a power system can stop working and the remaining converters
will continue to provide power to the load without interruption or shutdown. The load sharing effectiveness
between paralleled units decreases as the number of units in the parallel group increases. As the number of
units increase, the output current-share disparity increases between the unit that delivers the most amount
of current and the unit that delivers the least amount of current. This causes the unit that delivers the most
amount of current to exceed its maximum operating current before most of the other units in the group. This
effectively limits the amount of current that an analog parallel system can deliver without any one unit exceeding
its operational current limit.
However, for converters that are designed to work in current limit indenitely, the current-share algorithm can
help achieve maximum output power without any one unit exceeding its maximum operating current limit. These
converters act as current sources when their current limit is exceeded. They have a congurable current limit.
These converters can load share by simply connecting their outputs in parallel or in conjunction with the analog
paralleling method to improve load sharing effectiveness at near full load. In general, the converter with the
highest output voltage will supply most of the current until the current limit is reached. As the load increases, the
output voltage of the converter will droop as it tries to maintain constant current. This output voltage droop will
then cause the other converters in the system to increase their output currents and reduce the current mismatch
among the units. This method can be used in conjunction with the analog method, if available in the converters
being paralleled to enhance paralleling effectiveness.
Digital Method:
The digital current-share method utilizes a high-speed, two-wire serial communication bus to implement current
share. With this method, on initial startup one converter automatically becomes the master and all the remaining
converters become slaves. The master unit then broadcasts its control state over the shared serial bus on
a cycle-by-cycle basis. The slave units interpret and implement the control commands sent by the master,
mirroring every action of the master unit. If the master is disabled or encounters a fault condition, all units will
immediately shut down, and if the master unit is unable to restart, then one of slave unit will become master.
If a slave unit is disabled or encounters a fault condition, all other units can continue to run assuming that the
load does not exceed the combined output power of the units. The slave unit which shutdown, may attempt to
restart seamlessly if not disabled or damaged. The accuracy of current-share among the paralleled converters
will depend on a symmetrical layout that ensures the same input and output impedances from each converter to
the common connected point and not the number of converters being paralleled.
Droop Method:
The droop load share method is very scalable and requires no active communication between the units. The
output voltage of the droop share units droop as output current increases. Systems designed for the droop
current-share method reduce their output voltage as the output current increases. At lighter loads, the output
voltage is higher and at heavier loads it is lower. This is graphically represented as output voltage vs. output
current, known as a load-line, and it slopes downward as current is increased. Converters connected in parallel
using the droop share method will share the current in accordance with how well their load-lines are matched
and also how well the external output impedances between the converters and the common connected points
are matched. You can nd the load-line graph in the datasheet of each of the system products. The advantage
of this method of paralleling is ease of implementation since there is no share bus or serial communication
between modules.