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R&S®Essentials | Power supplies fundamentals

Understanding Series and parallel operation

Author: Paul Denisowski, Test & measurement expert

The following will explain how multiple power supply channels can be connected in series or in parallel to increase their maximum output voltage or current.

Many DC benchtop power supplies have multiple channels and in most cases these channels are used independently to provide power to separate devices or loads. It is often also possible to combine the outputs of multiple power supply channels to increase the output voltage or current beyond that which can be provided by a single channel.

The only requirements for combining channels in this way is that the channels must be floating and galvanically isolated:

Floating: the channels are not connected to the common instrument ground
Isolated: the channels are independent of each other with no current flow between them

There are two ways power supply channels can be combined. If the channels are connected in series, this enables higher voltages. If the channels are connected in parallel, this enables higher currents. These connections are typically made externally, although in some cases these connections may be made within the supply itself.

Series operation in DC benchtop power supplies

Series operation combines channels to produce higher voltages than would be possible with a single channel. In this example, four channels with a configured output of 25V are each connected in series. The result is a combined output voltage of 100V.

Note that the channels don’t all have to be the same voltage.

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Note that the channels don’t all have to be the same voltage.

When connecting channels in series to obtain higher voltages, it is important not to exceed the maximum voltage-to-ground rating of any channel. This maximum channel voltage is usually higher than the maximum output voltage but is still limited.

Using the tracking function, voltage and current are adjusted simultaneously on all selected channels.

1. For example, this power supply channel can produce up to 64V on a single channel and has a maximum of 250V to ground. Connecting the negative terminal to ground and configuring maximum output voltage, results in 64V across the channel relative to ground.

2. If the negative terminal of this channel were instead serially connected to a voltage source producing 36V, the channel has 100V across it, which is still within the 250V limit.

3. If the series-connected input voltage to this channel were increased to 200V, then the channel would have a total of 264V across it, exceeding the maximum voltage to ground of 250V, and potentially creating a damaging or dangerous situation.

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Parallel operation in DC benchtop power supplies

Parallel operation is used to produce higher currents. In this example, four channels are set to 2V, but each channel can only source up to 10A. Combining these channels in parallel still results in only 2V across the load, but the combined channels can now deliver up to 40A through the load.

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For parallel operation in constant voltage mode and serial operation in constant current mode, certian rules have to be observed when configuring the channels in order to reasonably distribute power, voltage and current among the channels. The R&S®NGA102and R&S®NGA102power supplies support channel fusion. With serial or parallel channel fusion, the device acts like a single-channel power supply offering double the voltage or current range. In serial mode, the outputs are connected internally, while parallel mode requires external wiring.

Summary

Every power supply channel has a maximum output voltage and current.
To obtain higher voltages or currents, multiple power supply channels can be combined.
- Series connections increase the maximum achievable output voltage
- Parallel connections increase the maximum output current
For series connections, it is important not to exceed the maximum voltage-to-ground rating for each channel.

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