March, 2015
www.us-
tech.com
Page 65 Probing Power Supplies for Use with Test Equipment Continued from page 63
do not specify common-mode noise performance in their documentation, test equipment designers may be unaware of the amount of common- mode noise that may be produced by the power supply. Power supplies such as the TU425 series models from SL Power Electronics Corp. not only have minimized levels of com- mon-mode noise, but characterized and documented common-mode noise. This ensures that equipment designers can potentially save time and effort since they will not need to characterize a power supply’s com- mon-mode noise profile themselves. Other noise issues can be
caused by noise radiating from the power supply or conducted along the DC power lines onto system circuits and, conversely, back to the AC source. A power supply that mini- mizes noise levels can ensure system compliance with emissions stan- dards. In addition, less effort is required from the system designer during instrument development. Test equipment, as with many appli- cations, must comply with certain levels of EMI. Both radiated emis- sions (RE) and conducted emissions (CE) must be within either class A or class B of CISPR22/ EN55022/FCC Part 15 requirements, depending on the application. Open-frame power supplies typically meet class B for CE, and class A for RE. Power sup- plies are normally tested with resis- tive loads when certifying their per- formance to these standards. This sometimes presents a challenge to equipment designers because once the power supply is integrated in test equipment, the EMI profile will typi- cally change, due to other factors, such as cables and ground configura- tions. A power supply that is designed to meet these standards with some level of margin provides test-equipment designers with a bet- ter chance of maintaining compliance in their equipment. Using such a power supply can also minimize material costs and cut material costs in developing an instrument. Test equipment may operate in
many environments, from research labs to production lines. The equip- ment is expected to operate reliably under all conditions for which it is specified. Unstable power sources, noisy (electromagnetic) environ- ments, etc., can affect the operation of a power supply, and therefore, the system within which it is used. An AC source can introduce
electrical phenomena that can cause system disruption and/or affect per- formance. Power
surges and
brownouts, for example, can cause a system shutdown unless such phe- nomena are managed. A power sup- ply that can “protect” the system from these phenomena will ensure continued operation of the equip- ment.
To provide the best protection
against external influences, compli- ance with the highest levels of elec- tromagnetic compatibility (EMC) standards is required. Typical EMC standards are IEC61000-4-x, with the “x” being one of the numbers denoting a specific section of the standard. Most power supplies com- ply with various levels of certain sec- tions of the IEC61000 standard. The IEC 61000-4-2 standard defines four levels of electrostatic-
discharge (ESD) protection, using two different testing methodologies. Contact discharge involves discharg- ing an ESD pulse directly from the ESD test gun that is touching a device under test (DUT). The other test method, air discharge is the other, brings the ESD test gun close to a DUT until a discharge occurs:
l Levels 1 and 2 are reserved for
which is sparsely but not continu- ously handled. l
Level 3 is used for equipment
equipment installed in a controlled environment and in the presence of antistatic materials. l
ment which is continuously handled. For most test equipment which
Level 4 is required for any equip-
comes in contact with operators reg- ularly, level 4 (8kV contact test, 15kV air test) would provide the best protection for all environments.
IEC61000-4-5 Standard The IEC61000-4-5 standard
relates to the immunity require- ments, test methods, and range of recommended test levels for equip- ment to unidirectional surges caused by over-voltages from switching and lightning transients. Several test lev- els are defined which relate to differ- ent environment and installation conditions. These requirements are developed for and are applicable to all types of electrical and electronic equipment, including test equip-
ment. Areas around the world where unstable and unconditioned AC sources provide the power for test equipment — in laboratories, in fac- tories, etc. — will potentially subject the equipment to various surges that could potentially shut down or even damage the equipment. Power sup- plies such as the TU425 series mod- els are compliant to level 4 (4kV), offering superior protection against high levels (2kV line-line, 4kV line- ground) of input surges. The IEC61000-4-11 standard
defines the immunity test methods and range of preferred test levels for electrical and electronic equipment connected to low-voltage power sup-
Continued on page 69
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104