Why a Power Supply with Data Bus?
2021. 11. 12
Manufacturers of power supplies have recently started to offer interfaces for controlling and monitoring their power supplies. This article highlights the reasons for this and the prospects for circuit designers.
Let us think of applications that demand high power from the supply, but only for a comparably short duty cycle. Thus, the average power required is significantly lower. Such applications could be high-power equipment like 3D printers, laser cutting, or a robotic arm that needs to be moved quickly but remains stationary most of the time. Developers of such devices might be tempted to recommend a power supply that is capable of permanently delivering the highest power peak to be expected ('worst-case load current'). However, this approach would result in a higher-cost power supply that is less efficient and may introduce operational hazards. Since, in the event of a fault, the excessive current delivered to the load could be high enough to start a fire.
So a better approach is to choose a smaller power supply that can deliver high power peaks for a specified short time while limiting the current in the event of a persistent fault. The type of electrical load determines when and how much power is required. The developer should adopt a consumer-oriented approach, allowing for programmable power supply behavior. When it comes to such requirements, a digital interface is usually preferred over analog controls. This is especially true when monitoring functions are integrated into the power supply unit.
How much current is flowing? Is it within expected limits, or is the load behaving abnormally? With the appropriate intelligence implemented in the power supply and a suitable data bus available, monitoring all connected loads becomes more reliable and straightforward. The PMBus® (Power Management Bus), which is built into many modern power supplies, has established itself for all these tasks.
So a better approach is to choose a smaller power supply that can deliver high power peaks for a specified short time while limiting the current in the event of a persistent fault. The type of electrical load determines when and how much power is required. The developer should adopt a consumer-oriented approach, allowing for programmable power supply behavior. When it comes to such requirements, a digital interface is usually preferred over analog controls. This is especially true when monitoring functions are integrated into the power supply unit.
How much current is flowing? Is it within expected limits, or is the load behaving abnormally? With the appropriate intelligence implemented in the power supply and a suitable data bus available, monitoring all connected loads becomes more reliable and straightforward. The PMBus® (Power Management Bus), which is built into many modern power supplies, has established itself for all these tasks.
PMBus properties
The Power Management Bus (PMBus®) is an open standard for a digital energy management protocol: simple, robust and extensible. About 40 PMBus member companies adopt, promote and improve this standard.
The PMBus allows engineers to set operating parameters for one or more power supplies. For example, a power supply unit can be switched off completely when it is not needed, or the output voltage and current can be dynamically adjusted. A programmable fan power supply connector can be used to convert a normal fan into an intelligent one: Fan activity and fan speed are automatically adjusted based on output power requirements, reducing noise and extending service life. All these functions are supported by a standard PMBus, which also includes the I2C protocol for compatibility with most microcontrollers.
Just as important as PMBus command control are its monitoring capabilities. The PMBus provides real-time status data such as input/output current and voltage, power consumption, critical component temperature, and detailed fault diagnostics. With this information, applications can detect potential overload or thermal conditions before they become critical. If the internal temperature rises due to insufficient cooling, the power supply does not simply shut down but issues a warning before reaching unsafe levels.
But the PMBus is not just for monitoring and control. The bus connects directly to the internal microcontroller in the power supply, which controls the digital feedback loop. This means engineers can set and monitor operating parameters while also adjusting transient response, slew rates, and compensation matrices. These capabilities allow the power supply to be dynamically adjusted to match application load conditions. In short, adding a PMBus interface transforms a standard power supply into a customizable solution.
The PMBus allows engineers to set operating parameters for one or more power supplies. For example, a power supply unit can be switched off completely when it is not needed, or the output voltage and current can be dynamically adjusted. A programmable fan power supply connector can be used to convert a normal fan into an intelligent one: Fan activity and fan speed are automatically adjusted based on output power requirements, reducing noise and extending service life. All these functions are supported by a standard PMBus, which also includes the I2C protocol for compatibility with most microcontrollers.
Just as important as PMBus command control are its monitoring capabilities. The PMBus provides real-time status data such as input/output current and voltage, power consumption, critical component temperature, and detailed fault diagnostics. With this information, applications can detect potential overload or thermal conditions before they become critical. If the internal temperature rises due to insufficient cooling, the power supply does not simply shut down but issues a warning before reaching unsafe levels.
But the PMBus is not just for monitoring and control. The bus connects directly to the internal microcontroller in the power supply, which controls the digital feedback loop. This means engineers can set and monitor operating parameters while also adjusting transient response, slew rates, and compensation matrices. These capabilities allow the power supply to be dynamically adjusted to match application load conditions. In short, adding a PMBus interface transforms a standard power supply into a customizable solution.
The RACM1200-V
One power supply that includes all the features mentioned above is RECOM's RACM1200-V. This series sets a new standard for compactness in the AC/DC power supply class, designed for reliable, fanless operation to support long-term system availability. The baseplate-cooled design efficiently directs heat away from the application for improved performance, enabling continuous output power up to 1,000W, with short-term output power reaching 1,200W. With an optional external fan connected to the fan output, this power supply can sustain 1,200W continuously.
A versatile range of output voltage settings and a combination of constant voltage/power and hiccup-mode settings enhance the product’s intrinsic safety. Various analog control and monitoring functions are available via the connector, as well as two auxiliary outputs: a programmable 5V to 12V system fan output and an isolated 5V/1A standby output for housekeeping functions.
The RACM1200-V series incorporates intelligent, controlled, and fault-limiting features, enabling project-dependent firmware configurations for inherently fail-safe operation. In the standard version, internal status can be accessed through two signal lines and an indicator LED:
Fig. 2: Excerpt from RACM-1200V data sheet
In addition to analog status and control pins, the PMBus-enabled RACM1200-V/PMB offers a digital interface allowing for real-time adjustments to the power supply. RECOM also provides a command-line interface utility for programming the power supply. On request, the device can be pre-configured with custom firmware settings.
Both versions achieve peak efficiency of up to 95% and comply with eco-design standards for standby mode. The RACM1200 series holds worldwide safety certifications for medical (2MOPP, BF), industrial and ITE standards, along with EMC compliance for Class A immunity and Class B emissions. These features make it one of the most easily integrated modular power supply solutions available.
A versatile range of output voltage settings and a combination of constant voltage/power and hiccup-mode settings enhance the product’s intrinsic safety. Various analog control and monitoring functions are available via the connector, as well as two auxiliary outputs: a programmable 5V to 12V system fan output and an isolated 5V/1A standby output for housekeeping functions.
The RACM1200-V series incorporates intelligent, controlled, and fault-limiting features, enabling project-dependent firmware configurations for inherently fail-safe operation. In the standard version, internal status can be accessed through two signal lines and an indicator LED:
Fig. 2: Excerpt from RACM-1200V data sheet
In addition to analog status and control pins, the PMBus-enabled RACM1200-V/PMB offers a digital interface allowing for real-time adjustments to the power supply. RECOM also provides a command-line interface utility for programming the power supply. On request, the device can be pre-configured with custom firmware settings.
Both versions achieve peak efficiency of up to 95% and comply with eco-design standards for standby mode. The RACM1200 series holds worldwide safety certifications for medical (2MOPP, BF), industrial and ITE standards, along with EMC compliance for Class A immunity and Class B emissions. These features make it one of the most easily integrated modular power supply solutions available.
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