Many industrial functions within the automotive, automation, equipment, or medical sectors require energy provides that adjust to useful security requirements. If the enter voltage of such an influence provide is just not inside its specification, the system to which it’s supplying energy is probably working in an unsafe state. Monitoring enter and output voltages for faults comparable to undervoltage, overvoltage, and overtemperature might require resetting and transitioning the system to a secure state.
Defining the protections wanted to adjust to useful security requirements is dependent upon the protection stage, which the design engineer should decide in cooperation with a security inspection company comparable to Technischer Ãœberwachungsverein. The engineer should additionally work on a time-consuming danger evaluation of failures that deal with each secure and harmful failures in addition to random and systematic failures.
Practical security in energy provides
Security requirements comparable to IEC 61508 or ISO 13849A specify the utmost allowable likelihood of harmful failures per hour.
The necessities for a secure energy provide as laid out in IEC 61508, which covers useful security in industrial manufacturing, embrace overvoltage safety with security shutoff, secondary-side voltage management with security shutoff, and power-down with security shutoff. These protections require important extra exterior circuitry across the switched-mode energy provide (SMPS).
A secure energy provide should additionally fulfill random {hardware} fault necessities. Utilizing an built-in PG pin as the protection mechanism to observe failures may be inadequate, as a result of this pin is usually not unbiased; it shares the identical inner band hole with all security and monitoring options. A drifting band hole will trigger the PG pin to fail. This is named a common-cause failure, which doesn’t meet useful security necessities.
As proven in Determine 1, detecting any fault can even require extra supply-voltage supervisors in addition to a change linked in collection to the enter; alternatively, the change might connect with the output. This change disconnects the system from the supply or load in case of a failure. Redundant supply-voltage supervisors monitor the enter and output voltages. Sometimes, an industrial energy provide is proscribed to lower than a 60-VDC enter, even within the occasion of a fault, requiring an extra circuit with transient voltage suppression and a fuse, as a result of not all gadgets are specified to 60 V.
Determine 1 An industrial secure energy provide instance block diagram. Supply: Texas Devices
The change on the enter, which is below the management of the monitor, can take away energy in case of a failure. The enter and output voltage are monitored constantly. As I discussed earlier, to adjust to useful security requirements, all components should function inside a specified working voltage. That’s not a simple job, given the requirement to detect undervoltage and overvoltage occasions instantly.
Buck converter
Utilizing a functional-safety-compliant buck converter with built-in security options can drastically cut back the quantity of exterior circuitry, as proven in Determine 2. An built-in redundant circuit, which replaces the exterior voltage supervisor, has a startup diagnostic examine and might detect the failure of a FET. This implementation reduces the general value of designing a secure energy provide.
Determine 2 Built-in useful security options substitute an exterior voltage supervisor, decreasing circuit complexity. Supply: Texas Devices
The nFAULT pin within the converter is used for overvoltage safety and as a failure flag. Triggering the nFAULT pin disables a security change, which on this case is a perfect diode controller linked to the enter. The Temp pin communicates the temperature to a microprocessor and forces a shutdown if the temperature is simply too excessive. The VSNS pin has suggestions path failure detection, and there may be one other suggestions divider for redundancy. Throughout startup, the LM68645-Q1 buck converter checks the configuration on the RT, FB, and VSNS pins.
Determine 3 reveals a block diagram of a common board (configurable to fulfill totally different security requirements)—with an enter voltage vary of 19.2 V to twenty-eight.8 V and a most 60 V—for a secure energy provide.
A synchronous buck converter generates a 5-V output with a most present of three A. Beside the buck converter is a perfect diode with back-to-back MOSFETs linked to the enter. An excellent diode connects to the output. The nFAULT pin can management each switches. Two extra supervisors for redundant voltage monitoring on the enter and output can disable each switches as effectively. The perfect diode controller has power-path management and overvoltage safety. The voltage supervisors additionally present built-in self-test and overvoltage and undervoltage safety.
Determine 3 The TI Industrial 24 V to five V secure energy provide reference design, the place numerous redundant choices on the board make it attainable to adjust to totally different useful security requirements. Supply: Texas Devices
A buck converter designed to assist meet useful security requirements reduces the quantity of crucial useful security documentation, system value, and time to market. As a result of the entire gadgets within the 24 V to five V secure energy provide reference design are specified for ≥ 60 V, an enter transient voltage suppressor or fuse is just not crucial.
Upgrading a secure energy provide
Though upgrading a secure energy provide to a better customary requires important effort, it’s attainable to design an influence provide that meets useful security necessities but in addition decreases time to market and system value. Utilizing a buck converter with built-in security options helps obtain systematic and random {hardware} metrics and reduces the wanted exterior circuitry.
Florian Mueller is a techniques engineer and Member Group Technical Employees in TI’s Energy Provide Design Providers group. He has a grasp’s diploma in electrical engineering from the Technical College of Haag, Germany. Florian’s predominant focus lies on industrial high-voltage designs for various finish tools.
Associated Content material
- Attaining useful security: Managing random failures
- Motor management for useful security
- Enabling useful security in automotive processors
- Designing energy provides for industrial useful security, Half 1
- Approaches to useful security in automotive design
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