In certain scenarios, relying on a solitary power supply may prove inadequate in meeting the energy demands of a load. Multiple power supplies are employed for various reasons, such as enhancing reliability through redundancy or achieving higher output power. However, when delivering power collectively, it becomes crucial to ensure a harmonious distribution among all the power sources.
Redundant power supplies encompass a configuration in which the outputs of numerous power sources are interconnected, aiming to enhance the system’s dependability rather than its power output. Typically, redundant setups are meticulously devised to draw output current solely from the primary power supplies. However, in the event of a failure in one of the primary power sources, the backup power supplies come into play, providing the necessary current. By refraining from drawing load current from the redundant supplies unless a problem arises with the primary sources, the system ensures high reliability.
Power supplies A and B share similarities as they both possess identical Vout and maximum Iout capabilities. The voltage across the load matches the voltage supplied by these power sources. Similarly, the maximum current that the load can draw corresponds to the maximum output current of a single power supply. By utilizing an electronic switch, one of the power supply outputs can be connected to the load.
To amplify the generated power, a commonly employed technique involves linking the outputs of two or more power sources in a parallel configuration. In this setup, each power supply is responsible for providing the necessary voltage to the load, while connecting them in parallel enhances the available load current and, consequently, the overall load power.
Implementing this topology successfully requires careful considerations to ensure its efficiency. In parallel configurations, power supplies with built-in circuits are preferable, as these internal circuits contribute to improved current sharing efficiency. However, if the power supplies utilized in a current sharing application lack internal sharing circuits, alternative external methods must be employed, albeit with potentially lower efficiency.
The primary concern revolves around achieving an even distribution of load current among the power supplies. This distribution relies on both the design of the power supplies themselves and the design of the external circuitry and conductors employed to connect the supply outputs in parallel. Typically, identical supplies are used when configuring them in parallel, given the challenges associated with efficiently aligning different power supply configurations. Nonetheless, it is feasible to parallelize supplies with matching output voltages while having non-matching maximum output currents.
Power supplies A and B must maintain identical output voltages, while their maximum output currents can differ.
The voltage across the load matches the voltage provided by the power supplies.
The maximum current drawn by the load is equal to the combined maximum output current of both power supplies.
The current monitoring circuits evenly distribute the load current between the power supplies.
An alternative method to enhance the power delivered to a load involves linking the outputs of multiple power supplies in a series arrangement rather than in parallel. Employing a series topology offers several advantages. Firstly, it enables nearly flawless utilization of power delivery from the supplies, eliminating the need for circuit configuration or sharing. Additionally, it exhibits tolerance towards a wide range of application designs. In contrast, when power supplies are connected in parallel, each supply contributes the required voltage while the load current is shared among them. Conversely, connecting power supplies in series ensures that each supply provides the necessary load current, resulting in the load receiving a combined output voltage from the series-connected supplies.
It is important to note that when configuring power supplies with series-connected outputs, the supplies do not have to possess similar output characteristics. The load current will be limited to the lowest capability among the supplies in terms of load current, while the load voltage will be the sum of the output voltages from all the supplies in the string.
However, there are certain limitations imposed on power supplies when used in a series output configuration. One such limitation is that the supplies’ outputs must be designed to withstand the voltage offset caused by the series connection. This offset voltage is generally not problematic, but it is crucial to avoid stacking the output voltages of ground-referenced power supplies onto the outputs of other supplies. Another limitation is the possibility of subjecting a supply’s output to a reverse voltage if that particular output is inactive while the remaining outputs in the series are active. To address this concern, a simple solution is to place a reverse biased diode across the output of each supply. The breakdown voltage rating of the diode must exceed the output voltage of each individual supply, and the diode current rating should be greater than the highest output current rating among all the power supplies in the series string.
Power supplies A and B possess the capability of delivering varying maximum output voltages (Vout) and maximum output currents (Iout). When these supplies are connected, the load voltage can be calculated by adding together the output voltages of both supplies. Moreover, the maximum load current is determined by the lower value between the maximum output currents of either supply. To safeguard the outputs of the supplies, reverse bias diodes are implemented.
When power supplies are connected in parallel, there is a drawback in terms of power utilization due to the tolerance of current sharing control between the supplies. To overcome this issue, a special circuit is required to regulate the current sharing between the supplies. Additionally, the design and construction of the conductors connecting the supplies in parallel need to be carefully considered, as they can significantly impact the overall performance. Ideally, it is best to use similar power supplies for easy design and compatibility.
On the other hand, when power supplies are connected in series, power utilization becomes more efficient, with the limitation being the output voltage accuracy of each individual supply. The advantage of this configuration is that there is no need for any circuits to control voltage or current sharing between the supplies. Furthermore, the design or construction of the conductors connecting the supplies in series does not affect their performance, making it a simpler and more versatile option. In this case, power supplies of different combinations can be easily designed and utilized.
While connecting power supplies in parallel is a common method to increase the load power delivered, it is worth considering the alternative of connecting the outputs of multiple power supplies in series. Power supply vendors, such as ALEXANDER ELECTRIC, have technical staff who specialize in assisting customers to configure suitable solutions for various power supply application challenges.