learn to connect power supplies in parallel for higher current output

7/29/2019 Learn to Connect Power Supplies in Parallel for Higher Current Output

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Learn to connect power supplies in parallel for higher current output.

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Two or more power suppli es can be connected to supply higher voltages or current. The sim plest method to create higher

current is to connect the power supplies in parallel and leave only one supply in constant voltage mode. Some power

supplies are equipped with analog control signals that allow auto-parallel or auto-tracking, a more elegant way to control

multiple power suppl ies. Auto-parallel suppli es can be controlled with a single mas ter supply; a second advantage is that

all of the master power supplies features can be us ed. e.g. remote sense, CV or CC mode, even analog program ming.

Auto-tracking allows mul tiple suppl ies to track the mas ter, the slaves can have the sam e output characteristics or can be

configured to be proportional to the mas ter.

1) CONNECTING POWER SUPPLIES IN PARALLEL TO PRODUCE HIGHER CURRENT

Two or more power suppli es being capable of CV/CC automatic cross over operation can be connected in parallel to

obtain a total output current greater than that available from one power supp ly. The total output current is the s um of the

output currents of the individual power s upplies . The output of each power s upply can be set separately. The output

voltage controls of one power supply should be set to the desired ou tput voltage (CV); the other power supplies should be

set for a slightly higher output voltage. The supplies with the higher outputvoltage s etting will provide constant current

output, and will drop their output voltage until i t equals the output of the CV supply.

Connecting two or more power suppli es in parallel (Figure 1) provides higher currents. It is important to follow these

precautions:

1. One unit must operate in cons tant voltage (CV) mode and the other(s) in cons tant current (CC) mode.

2. The output load mus t draw enough current to keep the CC unit(s) in CC mode.

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Figure 1: Three power suppl ies connected in parallel to produce addi tional current.

Setting Voltage and Current. Program the current limit o f each power s upply to its maximum value. Next, set the output

voltage of the CV supply to a value s lightly lower than the CC uni t(s). The CC units s upply the maximum output current that

they have been set to and drop their output voltage until it matches the voltage of the CV unit, which supplies only enough

current to fulfill the total load dem and. The current supplied to the load will be the sum of the current from each s upply. To

learn more about constant current and voltage modes see: How do I put the power s upply in the constant current mode?

2) AUTO-PARALLEL OPERATION

Auto-parallel operation permi ts equal current sha ring under all load condi tions , and allows com plete control o f output

current from one m aster supply. The control unit is called the mas ter; the controlled units are called slaves. Normally, only

supplies having the sam e model num ber should be connected for auto-parallel operation, since the supplies m ust have

the same voltage drop across the current monitoring resistor at full current rating. The output current of each slave is

approximately equal to the mas ter's. Figure 2 s hows the rear panel terminal connections for auto-parallel operation of

three E36xx- series supplies.
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Figure 2: Auto-parallel ope ration of three E36xx-series power supplies.

Setting Voltage and Current. Turn the slave unit's CURRENT control fully clockwise. Adjust the m aster unit's controls toset the desi red output voltage and current. The master supply operates in a completely normal fashion and may be s et up

for either constant voltage or constant current operation as required. Verify that the slave(s) are in CV operation. For auto-

parallel operation of three supplies , the combined output voltage is the same as the master unit's voltage setting, and the

combined output current is three times the master unit's current. In general, the auto-parallel output current (Io) is Io = Im +

Is1 + + Is2 + . . Isn = n (Im); where Im = master unit's output current and IS = slave unit's output current.

Proportional currents from auto-paralleled units require equal load plus lead voltage drops. Connect each supply to the

load using separate pairs of wire with length chosen to provide equal voltage drops from pair to pair. If this is not feasible,

connect each supply to a pair of distribution terminals using equal- voltage-drop wire pai rs, and then connect the

distribution terminals to the load with a single pair of leads.

Overvoltage Protection.Adjust the des ired OVP shutdown limit us ing the master un it's OVP Adjus t control. Set the slave

units' OVP limits above the master's. When a mas ter-unit shuts down, the mas ter programs the s lave units to zero voltage

output. If a slave unit shuts down, it shuts onl y itself down. If the required current is great enough, the m aster will s witch


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from CV to CC operation.

Remote Sensing. To remote sense wi th auto-parallel operation, connect remote-sense leads only to the master unit

according to the remote-sens ing ins tructions.

Remote Analog Voltage Programming. To remote program with auto-parallel operation, set up only the master unit for

remote programming according to the remote-programming instructions.

3) AUTO-TRACKING OPERATON

Auto-tracking operation of power supplies is sim ilar to auto-parallel opera tion except that the master and s lave supplieshave the sam e output polarity with respect to a common bus or ground. This operation is us eful where sim ultaneous

turn-up, turndown or proportional control of all power supplies is required. Figure 3 shows three supplies connected in

auto-tracking with their negative output terminals connected together as a common or ground point. For two or more uni ts

in auto-tracking a fraction R2/(R1+R2) of the output of the mas ter supply is provided as one of the inputs to the

comparison amplifier of the slave supp ly, thus controlling the slave's output. The master supply in an auto-tracking

operation mus t be the positive supply having the larges t output voltage. Turn-up and turndown of the power suppl ies are

controlled by the master supply. In order to m aintain the temperature coefficient and stabili ty specifications of the power

supply, the external resis tor should be s table, low noise, low temperature.


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Figure 3: Auto-tracking operation of three E36xx-series supplies .

Determining Resistors. External resis tors control the fraction of the master uni t's voltage that is supplied from the slave

unit. The output of slave one is determined by the ratio R2/(R1+R2) = (Vs1/Vm), and the output of slave two is determined

by the ratio R4/(R3+R4) = (Vs2/Vs1).

Where Vm = mas ter output voltage

Vs = slave output voltage

A 0.1 F capacitor in para llel wi th R2 and a 0.1 F capacitor in pa ralle l with R4 can help ensure the stab le operation.

Setting Voltage and Current. Use the master unit's VOLTAGE control to set the output voltage from both units. When the

master is in CV operation, the master's output voltage (Vm) is the same as its voltage setting, and the s lave's output

voltage will be determined by the ratio of the resistors. The VOLTAGE control of the slave unit is disabled. Set the


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CURRENT controls of m aster and s lave units above the required currents to as sure CV operation of master and slave

units.

Over voltage protection. Set the OVP shutdown voltage in each unit s o that it shuts down at a voltage higher than its

output voltage during auto-tracking operation. When a m aster unit s huts down, it p rograms any slave units to zero output.

When a slave unit shuts down, it shuts down only itself.

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