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Receive good advice and save money.There is ever-greater uncertainty in relation to the EN61000-3-2 harmonics directive (mistakenly known as the PFC directive).
Constant variations to the directive and the new A14 amendment in autumn 2000 have led to unbridled confusion. Many customers, when faced with these doubts, prefer their products to include PFC to be sure that they comply with the directive.
If including PFC did not have an economic repercussion then including it in products would always be the best solution. It is important to determine if we really need PFC and the advantages that it provides. In many cases this directive will not affect you.
Answer some basic questions to see whether you need to comply with the directive:
EN61000-3-2 only affects a specific power range; in addition, there are various exceptions where the directive does not apply. If you answer "no" to any of the following questions then you need not comply with the directive.
Note: we must consider the product as one single unit connected to the mains supply, even if the system contains several components.
2. Is power consumption continuously in the range of 75 W to 1000W?
Note: consumption is only considered (for all phases) during normal operation. Operation under extreme conditions or the rated power of the equipment are not considered. In other words, we only consider the real consumption of the equipment.
3. Is the input voltage of your product between 220 and 415 VAC?
4. Does your equipment operate in the EU?
Note: Outside the European Union compliance with EN61000-3-2 is only necessary if required by national law.
CAREFUL WITH EXCEPTIONS!
The directive only applies to a power range of 75 W to 1000W. Nevertheless, for some models it may seem that we are outside this range yet the directive is still applicable.
5. Limit of 1000W: if your product has a rated power of 1000W yet in reality it uses less power then the directive still applies. (Above 1000W there is no limit for compliance with the directive)
6. Increase in power due to parallel connections:
Three 70W devices operating individually need not comply with the directive. However, if when connected in parallel they consume more than 75 W then they must comply with EN61000-3-2 (though in many cases PFC will not be required in order to comply with the directive).
If your product falls outside the indicated limits then you need not comply with the directive. Below we will see more detailed information concerning this point. Nevertheless, we here clarify a couple of concepts which sometimes cause confusion:
7. ¡ CE+CE ? CE!:
Even though we only use components certified by the CE this does not mean that
we are complying with the directive. Operating conditions
(for example different types of power) or the applicable specifications for our product may be totally different (for example CE regulations for power supplies are different than those for toys). Nevertheless, compliance with the EN61000-3-2 directive is a prerequisite for the CE certificate.
8. Not just for switch mode power supplies. The directive also applies to linear power supplies (regulated or not). The combination of an input capacitor and a rectifier generates harmonics.
The following list helps us to decide whether our equipment (powered by a switch mode power supply) falls within the scope of EN61000-3-2. This list is complementary to the previous checklist.
9. Does the power supply function at its rated power for your product? Many designers overestimate the power requirements of the power supply in relation to the real consumption of the application. This reduces the temperature of the equipment, improves reliability and extends the expected lifetime of the product.
10. Equipment with a rated power input of up to 600W are really at the limit of requiring PFC.
11. If during normal operation the equipment consumes less than 150 W with a single power supply and with no additional parallel loads, then it will probably not need to use PFC (especially if they use PULS power supplies). However, each case must be studied separately.
12. Does your equipment require triphase or monophase consumption for parallel heavy loads (such as motors) using the power supply ? In this case the total power exceeds 1000W and PFC is not needed for the control electronics.
13. Does the equipment use forced ventilation? If yes, then the power source will reach temperatures less than those established and as such will generate less harmonics (see input NTC below).
What does EN61000-3-2 really mean?
the current which your product consumes from the mains supply is probably not in sinusoidal wave form. According to J B Fourier this deviation in the sinusoidal wave is due to the overlapping of sinusoidal waves oscillating over the fundamental frequency and over multiple values of this frequency (harmonics). EN61000-3-2 establishes the maximum values for these harmonics. Electrical charges may be divided into four classes:
Class A: equipment with balanced triphase input; equipment for domestic use which do not belong to class D; Non-portable devices; luminosity control devices for glow lamps; audio equipment; devices which do not belong to any other class.
Class B: Portable electrical equipment.
Class C: Lighting equipment
Class D: personal computers, monitors and televisions.
This classification of equipment was added in the A14 amendment to the directive. The PULS switch mode power supplies belong to class A.
In addition, the conditions for measuring dynamic charges are specified. Before the specifications for the tests were so confusing that the same product could pass the tests in one laboratory and fail in another :
· To ensure the consistency of the tests the load peaks are generated in a smoother fashion using an RC filter for periods of 1.5 seconds.
· The peak values for harmonics may reach 150% of the maximum established values. However, the total measurement for the period cannot exceed the maximum limits.
· For 10% of the test time the equipment may be in standby mode; this helps us to meet the requirements.
· The test conditions must be normal conditions or those established by the manufacturer's specifications. Extreme operating conditions must never be considered (such as starting the equipment). The current of harmonics is only measured in the L conductors and not in the neutral area.
EN 61000-3-2 and Power Factor Correction (PFC)
With Power Factor Correction (PFC) it is possible that the harmonics of the input electrical current may not exceed the maximum values indicated by the directive. Nevertheless, the important point here is to be within the indicated limits. The directive does not stipulate how this is to be achieved. Two possible principles exist: Passive PFC is an inductance ( PFC shock) in the equipment input circuit. It stores energy and reduces current pulses. Active PFC is connected to (or included in) the control electronics which supervise consumption from the electrical mains supply. Thus, power is consumed with a virtually sinusoidal form, the energy stored, and then transferred to the secondary circuit in a controlled manner.
Pros and cons: Passive PFC: simpler, cheaper, more robust, generates less heat and is easily integrated into existing designs. However, this system reduces harmonics, but does not eliminate them completely. There is a lower limit which can not be further reduced. For some heavy loads or for equipment powered by several power supplies connected in parallel this system may not be sufficient.
Active PFC practically eliminates all harmonics and offers better performance (even for difficult loads). Nevertheless, it generates more heat and its design is more complex, hence it is more expensive. It is suitable for new designs, but trying to include it in an existing design may be difficult and expensive.
NTC in the input: does temperature affect harmonics?
In power supplies where the start-up current is limited passively by an NTC, temperature has a real bearing on harmonics. At lower temperatures the NTC has a greater resistance and thus reduces harmonics more effectively. The equipment will therefore function more efficiently.
If these brief guidelines have not clarified whether you need a power supply with PFC or not, then please contact our technical department. We will help you save money.