ontent.
Power Supply Selection for Advanced Motion Controls Amplifiers and Drives Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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Page 1 of 11



Power Supply Selection
for Advanced Motion Controls Amplifiers and Drives




There are several factors to consider when selecting a power supply for Advanced Motion Controls servo
amplifiers.

1. Power
requirements
2. Isolation
3. Regeneration

4. Voltage
ripple

Power requirements
refers to how much voltage and current will be required by the amplifier(s) in the
system.
Isolation
refers to whether the power supply needs an isolation transformer.
Regeneration
is the
energy the power supply needs to absorb during deceleration.
Voltage ripple
is the voltage fluctuation
inherent in unregulated supplies.

Each consideration is discussed in detail in the following pages.

Section 1. Power Requirements
Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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I. Power Requirements

A system will need a certain amount of voltage and current to operate properly. If the power supply has
too little voltage/current the system will not perform adequately. If the power supply has too much voltage
the amplifier may shut down because of over voltage or worse, the amplifier may be damaged. The
processes of calculating the voltage and current requirements are described below.


1) Selecting the Supply Voltage

The ideal voltage is defined by the following constraints:

Upper Constraints
Amplifier
over
voltage
limit
Shunt
regulator
voltage

Lower Constraints
System
voltage
requirements
Amplifier
under
voltage
limit

The figure below illustrates the constraints when selecting a power supply voltage for the B25A20
amplifier to be used with a system that requires 100V to operate.


Figure 1.1. In this case the acceptable power supply voltage is between 110V and 170V.
Section 1. Power Requirements
Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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Calculations

Over Voltage The over voltage level on Advanced Motion Controls amplifiers can be found in the
amplifier data sheet. In the example from Figure 1.1. the data sheet for the B25A20 amplifier states that
the over voltage shut down point is 195V.

Shunt Regulator Voltage From figure 1.1 an SRST185 was chosen with a 185V shunt voltage. The
purpose of a shunt regulator is to clamp the power supply voltage so it doesnt exceed the amplifier over
voltage levels during regeneration. See section 3 (Regeneration) to determine if a shunt regulator is
required and how to select the correct voltage.

System Voltage Requirement The system voltage requirement is based on the motor properties and
how fast and hard the motor is driven. The system voltage requirement is equal to the motor voltage
required to achieve the move profile.

V
M

Motor Voltage:

(
) (
)
M
M
M
E
M
R
I
S
K
V + =
(1.1)

Where:

V
M

Motor Voltage (V)

I
M

Motor Current (A) (use the maximum current expected for the application)
K
E

Motor Back EMF Constant

R
M

Motor Line to Line Resistance ()

S
M

Motor Speed (use the maximum speed expected for the application)


If
I
M

is not known you can use the maximum current rating of the motor or amplifier or you can calculate
it:

I
M

Motor Current:

T
M
K
Torque
I
=
(1.2)


Where
K
T

is the motor torque constant.

Keep in mind the calculated value for V
M
is the minimum voltage required to complete moves at the
desired speed and torque. There should be at least 10% head room between the calculated value and
the actual power supply voltage to allow for machine changes such as increased friction due to wear,
change in load, increased operating speed and other changes.

Under Voltage Limit The under voltage level on Advanced Motion Controls amplifiers can be found in
the amplifier data sheet. In the example from Figure 1.1. the data sheet for the B25A20 amplifier states
that the under voltage shut down point is 40V.

Section 1. Power Requirements
Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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Acceptable Power Supply Voltage The power supply voltage needs to be at least 10% above the
system voltage requirement
and at least 10% below the lowest value of the following:

Shunt regulator voltage
Amplifier over voltage
Power supply over voltage

If possible 15% or more headroom should be used.


2) Selecting the Supply Current

The power supply current rating is based on the maximum current that will be required by the system. If
the power supply powers more than one amplifier then the current requirements for each amplifier should
be added together. Due to the nature of PWM amplifiers the current into the amplifier does not always
equal the current out of the amplifier, but the
power in
is equal to the
power out
. Use the following
equation to calculate the amplifier current requirements based on the motor current requirements.

I
PS

Power Supply Output Current:

(.98)
V
I
V
I
PS
M
M
PS
=

(1.3)


Where:
V
PS

Nominal Power Supply Voltage (V)
I
M

Motor Current (A)
eq(1.2)
V
M

Motor Voltage (V)
eq(1.1)

Use values of
V
M

and
I
M

at the point of maximum power in the move profile (when

V
M
I
M
= max). This
will usually be at the end of a hard acceleration when both the torque and speed of the motor is high.
(See figure 1.2 below)

Section 1. Power Requirements
Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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Figure 1.2. Power is equal to Torque x Velocity. V
M
and I
M
should be chosen where power is at the
maximum.

Note: The only time the power supply current needs to be as high as the amplifier output current is if the
move profile requires maximum current at maximum velocity. In many cases however maximum current
is only required at start up and lower currents are required at higher speeds.



Section 2. Isolation
Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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II. Isolation


There needs to be isolation between the AC line and the signal pins on the amplifier. If there is no
isolation, the amplifier will immediately fail when the amplifier signal ground is pulled to earth ground.
There are two options for isolation:

1. The amplifier can have built in optical isolation
2. The power supply can provide the isolation via an isolation transformer

The system must have at least one of these options to operate safely.


1) Amplifier With Isolation

Some Advanced Motion Controls amplifiers come with standard optical isolation, others have isolation as
an option, and some do not have isolation at all. To determine if an Advanced Motion Controls amplifier
has optical isolation look at the data sheet. The isolation will be indicated by a dashed line through the
functional block diagram and labeled as optical isolation. If the line is labeled
optional
optical isolation
then the part number determines if the amplifier has isolation. An amplifier has the optional optical
isolation if the letter I is between the base part number and the revision letter. Example: B30A8Q (no
isolation), B30A8IQ (isolation). If there is no dashed line through the block diagram the amplifier does not
have isolation.

The following are
some
of the Advanced Motion Controls amplifiers that come standard with optical
isolation:

Products that are rated to 400VDC
Amplifiers that take AC line voltage for power
Digital amplifiers



2) Power Supply With Isolation

An isolated power supply uses a transformer to isolate the AC line voltage from the power supply ground.
This allows both the power ground on an isolated power supply and the signal ground on a non-isolated
amplifier to be safely pulled to earth ground. Always use an isolated power supply if there is no isolation
on the amplifier. Section 3. Regeneration
Advanced Motion Controls 3805 Calle Tecate Camarillo, CA 93012
11/11/2003


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III. Regeneration

From Advanced Motion Controls Engineering and Installation notes:

During motor deceleration or a downward motion of the motor load, conversion of the systems mechanical
energy (kinetic and potential) will be regenerated via the servo amplifier back onto the supply in the form of
electrical energy.

This regenerative process can charge the capacitors in the power supply to potentially dangerous voltages
or voltages that may cause an amplifier over-voltage shutdown. Consequently, power supplies should have
sufficient capacitance to absorb thi