© aydindurdu dreamstime.com Application Notes | January 02, 2017
Active bridge rectifiers reduce heat dissipation within PoE security cameras
Power over Ethernet (PoE) has been embraced by the video surveillance industry as a solution to an age-old problem: complicated cabling.
This is a product release announcement by Linear Technology Corporation. The issuer is solely responsible for its content.
For instance, a basic, traditional fixed-view security camera requires two cables: one for power (10W to 15W from a 24V AC or 12V DC), and a separate, coax cable for the video signal. With PoE, a single Ethernet cable carries both video data and power. Everything is simplified. Right? Not quite. To meet compatibility with existing systems, camera manufacturers must produce PoE-enabled cameras that are also compatible with legacy power sources—they must accept PoE 37V to 57V DC from an RJ-45 jack or 24V AC, +12V DC, or –12V DC from an auxiliary power connector. The Old Way Loses Power Figure 1 shows the power architecture used by many PoE camera manufacturers to solve this problem. A full-bridge diode rectifier after the auxiliary (old-school) input produces positive DC power from either 24V AC, +12V DC or –12V DC. The resulting DC power and the PoE inputs are diode-ORed with the winning supply fed to a wide input voltage isolated switching power supply, which in turn powers the camera electronics. Figure 1. Auxiliary Input and PoE Power Architecture This power architecture presents a few challenges. When the camera is powered from the auxiliary input, three diodes (circled in Figure 1) fall into the power path. In addition to the inefficiency of this design and possible heat problems from the power dissipated by the diodes, the three diodes lead to a significant voltage drop at the input to the switching power supply. With a 10W to 15W camera, these challenges are easily surmountable, but the latest security cameras have doubled this power consumption. Features like pan/ tilt/zoom (PTZ) and camera lens heaters for outdoor operation have made this power architecture unsuitable for this new wave of cameras. To illustrate the architecture’s deficiencies, consider a 26W camera. For a 12V DC auxiliary input (assumed to actually be 9V DC due to use of unregulated wall warts/ AC adapters) and three 0.5V drop Schottky diodes, the input voltage of the switching power supply is 7.5V (9V – 3 • 0.5V). The input current for this camera is approximately 3.5A (26W/7.5V). The resultant power dissipation of the three Schottky diodes in the power path is 5.2W (3.5A • 3 • 0.5V). This power dissipation leads to higher temperature within the camera, which is difficult, time consuming and expensive to mitigate. Figure 2. Improved Power Architecture with No Diode Drops in Power Path Improve Performance with Ideal Diodes Figure 2 shows a way to counter this shortcoming. Here, the two diodes of the full-bridge rectifier are replaced by ideal diodes, circled (black) in Figure 2. Ideal diodes are simply MOSFETs controlled to behave like regular diodes. The advantage of an ideal diode is that one can use MOSFETs with low channel resistance (RDS(ON)), thus reducing the forward voltage drop (IDS • RDS(ON)) to much less than a Schottky diode drop. The LT4320 ideal diode bridge controller enables the control of four MOSFETs in a full-bridge configuration. The third diode drop due to the diode-OR in Figure 1 is eliminated by the LT4275 LTPoE++™/PoE+/PoE PD controller. Its topology allows the use of a few small-signal diodes, circled together (red) in Figure 2, for auxiliary input sensing. These diodes are not in the power path as in the traditional architecture, so they do not contribute any additional voltage drop or heat issues. Results The power architecture shown in Figure 2 significantly reduces overall power losses when compared to that of Figure 1. To quantify, the LT4320 combined with low channel resistance MOSFETs results in a 20mV drop across each ideal diode bridge MOSFET. This produces an input at the isolated supply of 8.96V (9V – 2 • 20mV). The higher input voltage drops the required input current to only 2.9A (26W/8.96V) versus the original 3.5A. The resulting power dissipation of the improved architecture is now a scant 116mW (2.9A • 2 • 20mV), versus 5.2W for the original architecture—a 45× reduction! Additionally, the lower input current further reduces power dissipation in the isolated power supply’s power components (i.e., input filter inductor, power transformer and switching MOSFETs) due to the reduction of their I2R power losses. A simple calculation puts this reduction at 31% (100% – 2.9A2/3.5A2). Conclusion Adding the LT4320 and LT4275 to the auxiliary and PoE inputs of a PoE-enabled security camera recovers more than 5W (5.2W – 116mW) of power dissipation over traditional full-bridge/diode-OR designs. This reduction of power eases the thermal design time and complexity of PoE security cameras. ----- Author: By Ryan Huff, PoE Applications Engineer, © Linear Technology Corp.
ASML ships first-generation multibeam inspection system ‘eScan1000’ ASML Holding NV says that it has completed system integration and testing of its first-generation HMI multibeam inspection (MBI) system for 5 nm nodes and beyond.
Cognex takes measures to counter deteriorating market conditions Machine vision technology provider, Cognex Corporation, says it is taking significant steps to reducing expenses due to deteriorating market conditions and to position the company for growth when conditions improve.
Verkotan selects PWC technology from Rohde & Schwarz Test and measurement specialist Rohde & Schwarz has recently introduced the R&S PWC200, the first plane wave converter (PWC) on the market. Verkotan is the first independent test house to choose this technology to test 5G NR FR1 base stations over-the-air (OTA).
Kurt Sievers takes the helm at NXP At its annual general meeting of shareholders, the appointment of Kurt Sievers as the company’s next CEO was overwhelmingly approved.
Excelitas’ Qioptiq subsidiary expands with new plant Excelitas Technologies, a company delivering photonic solutions, sats that its Qioptiq subsidiary held a ground-breaking ceremony last week to mark the beginning of construction for a new factory in Göttingen, Germany.
Farnell adds Sorensen power supplies to its roster Distributor Farnell announces that it has added Sorensen, the premier DC programmable power supply brand from Ametek, to its range of power supplies.
Infineon raises EUR 1 billion following successful share placement Infineon informs that the company placed 55 million new shares, following an accelerated bookbuilding process with institutional investors, under the exclusion of subscription rights. The shares were placed at a price of EUR19.30 per share, meaning that the company managed to raise EUR 1.06 billion.
Skeleton Technologies strengthens management with new COO Skeleton Technologies has appointed Ants Vill, former Vice President of Product, as Chief Operating Officer.
SiPearl chooses Germany for its first international operational subsidiary SiPearl, a designer of the microprocessor for the European exascale supercomputer, is opening its first international subsidiary in Duisburg, in the Ruhr region, Germany, in order to build closer connections with its German partners and future clients.
DELO reports increased revenues despite current pandemic DELO closed the financial year that ended on March 31 with a turnover of EUR 163 million. This is an increase of almost 5% compared to the previous year (EUR 156 million).
China falls far short of its "Made-in-China 2025" goal IC production in China represented 15.7% of its $125 billion IC market in 2019, up only slightly from 15.1% five years earlier in 2014. IC Insights forecasts that this share will increase by 5.0 percentage points to 20.7% in 2024 (one percentage point per year on average).
COVID-19 highlights the gravity of the secondary market for SME Cha Jin-Seok, Chief Financial Officer of SK Hynix, said it best in the company’s Q1 earnings call, “Because of a never experienced pandemic, even basic business activities such as maintaining normal operations and predicting future demand have become challenging tasks.”
GlobalFoundries to implement ITAR at US manufacturing facility GlobalFoundries plans to implement export control security measures at its most advanced manufacturing facility, Fab 8, in Malta, New York.
Rebound Electronics expands in Asia The independent supplier of electronic components says it is investing to increase its market coverage in Asia with the opening of several new offices and setting up a customer service & telesales centre.
Samsung expands foundry capacity with new production line Samsung Electronics says that it plans to boost its foundry capacity at the company's new production line in Pyeongtaek, Korea, to meet growing global demand for extreme ultraviolet (EUV) solutions.
Super Dry Totech expands Long Term Storage Solutions offering The most recent development for Super Dry Totech, is the acquisition of a new building to expand on capacity & to minimise risk by assuring continuity should a disrupting incident occur in one of the facilities.
Ynvisible acquires electrochromic display company rdot Printed electronics specialist, Ynvisible Interactive, announces that it will acquire the printed electrochromic displays business of rdot AB of Gothenburg, Sweden.Load more news
- COVID-19 highlights the gravity of the secondary market for SME
- Rolls-Royce takes heavy hit from COVID-19 – reduces workforce by 9000
- China falls far short of its "Made-in-China 2025" goal
- GlobalFoundries to implement ITAR at US manufacturing facility
- Data Link Solutions to provide MIDS cabinet terminals to US Navy