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Most Requested Product FAQs

• What are Y-Caps? Can I use another type of capacitor in my application?
• What is the difference between remote and local sense?
• Do the Vicor modules need a heat sink?
• What is PFC, and what does it mean to me?
• Why can't I use a MI-IAM (Input Attenuator Module i.e., MI-A22-MU) with a VI-200 DC-DC converter (i.e., VI-2W0-MW)?
• Can I solder wires directly to the pins of the Vicor module? And if not, what products can I use for direct wire connections?
• If I am not using the Gate In, Gate Out, or Trim pins on VI-200 / VI-J00 converters and the PC, PR or SC on the Maxi, Mini and Micro converters, can I leave them floating?
• Do I need filtering on the input and/or output side of the power converters?
• How do I create a negative output?
• Can the Three-Phase MegaPAC operate from a single-phase input?
• Why does the output power decrease if I trim the output voltage down?
• What is the switching frequency of your VI-200 / VI-J00 and Maxi, Mini and Micro converters?
• Do your modules load share?
• Do I need to fuse the input of the converter?

What is a Y-Capacitor? Can I use another type of capacitor in my application?

Power conversion modules generally require bypass capacitors from line to chassis (earth ground) to meet Agency EMI Standards by shunting common-mode noise currents and keeping them local to the converter. In cases where the converters are operating from rectified AC line voltage, the failure of a bypass capacitor could result in excessive leakage current to the equipment chassis, thus creating a ground fault and shock hazard. For this reason, a special classification of capacitor, referred to as a "Y-capacitor" is recommended. These capacitors contain a dielectric with unique "self healing" properties to help prevent against excessive leakage.

To meet general EMI/RFI requirements, Vicor recommends the use of Y-capacitors with all power conversion modules. Y-capacitors meet IEC384-14, EN132400 and UL1283 standards.

All applications utilizing DC-DC converters should be properly bypassed, even if no EMC standards need to be met. Bypass power input and output pins to each module baseplate. Lead length should be as short as possible. Recommended values vary depending on the front end, if any, that is used with the modules. In PC board-mount applications, each of these components is typically small enough to fit under the module baseplate flange.

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What is the difference between remote and local sense?

Local Sense involves using the power supply output power terminals as the sense points to provide feedback to the internal voltage regulation circuitry. Remote sense involves detection of output voltage at a point remote from the power supply, enabling the power supply to regulate output voltage and to compensate for voltage drop typically associated with long power cables. This permits greater accuracy of regulation than local sensing. The sense connections (from the sense pins) determine the regulation point, either at the converter output (local sense) or at the load (remote sense) to compensate for voltage drop. It is important to "close" the sense lines, i.e., +S to +Out, -S to Out, as described above for proper operation of the module; and it is an absolute MUST for Maxi and Mini modules.

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Do the Vicor modules need a heat sink?

This depends on a variety of factors within the application such as the maximum ambient temperature specific to the modules location, availability of forced convection cooling, loading characteristics and the converters efficiency. It is important to note that the advantage of a baseplated module versus the limitation of the open frame or bare-board converters is the flexibility of easily adding a heat sink to the baseplated module if needed.

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What is PFC, and what does it mean to me?

Todays electronic devices present a non-linear load to the ac source; that is, they do not draw a sinusoidal current when supplied from a sinusoidal voltage. The phase relationship between voltage and current may be very close but the shape of the current waveform differs greatly from the shape of the voltage waveform. This also results in a higher apparent power and a correspondingly reduced power factor. However, since there is no significant phase difference, the power factor can-not be said to be either lagging or leading.

Active Power Factor Correction (PFC) is the technique of controlling the current flow into the device to track the applied voltage waveform. A specific example of a non-linear load is a line-operated switching power supply with a capacitor input filter. This type of load draws no current until the line voltage is near the peak; then draws a large pulse of current as the voltage passes through the waveform peak. Power Factor Correction (PFC) would require the power supply to force the input current to have the same wave shape as the ac voltage source.

Advantages of PFC switching power supplies with a boost converter are: reduced input current for a given load power, improved ride-through energy storage because the energy storage capacitor is always charged to the maximum voltage, 85 – 264VAC operation without re-strapping the input, and compliance with EN61000-3-2. For additional information regarding PFC please see the Applications Notes section of the Vicor web site.

Recently, Amendment 14 to EN61000-3-2 was issued. One of the effects of this amendment was to reclassify AC-DC power supplies from Class D to Class A. Of significant importance in this reclassification is the elimination of the variable limit placed on harmonic currents. In its place, there is now a fixed limit based only on the maximum input power of the Class which is 1,000 watts. Since, in effect, AC-DC power supplies drawing less than 1,000W have had their harmonic current limit increased, there are now alternatives to active PFC for achieving EN compliance. The most simple, robust, reliable and inexpensive method of harmonic current reduction can now be employed in many lower power systems passive attenuation.

Another major advantage of this passive method is that, as the nomenclature implies, it doesnt rely on active components which contribute to a systems EMI level so it acts as additional line filtering that actually improves system EMI performance. The passive alternative: smaller, simpler, cleaner, cheaper is available as Vicors ENMods or Westcors FlatPAC-EN. Although passive harmonic current attenuation can improve power factor to about 0.8, it doesnt approach the near unity power factor of active PFC implementations such as Vicors VI-HAM or Westcors LoPAC Family.

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Why can't I use a MI-IAM (Input Attenuator Module i.e., MI-A22-MU) with a VI-200 DC-DC converter (i.e., VI-2W0-MW)?

The primary reason is related to input voltage range compatibility, i.e., the MI-A22-MU is designed for 18 50 V operation and the VI-2W0-MW is designed for 18 36 V operation, this is a critical difference especially for input transient protection. With respect to EMI / RFI, the obvious impact of the input range mismatch has prevented this filter from being offered with this converter and thus performance has not been characterized to the MI-IAMs published specifications and as such, cannot be guaranteed.

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Can I solder wires directly to the pins of the Vicor module? And if not, what products can I use for direct wire connections?

Vicor does not recommend direct wire connections to the module pins of its converters as the mechanical loading and thermal stress from bench soldering may cause potential reliability concerns. The modules are intended to be used in PCB applications with controlled soldering techniques per the Soldering Methods and Procedures Application Note. If chassis mounting is preferred Vicor offers packaging options for the VI-200/VI-J00 Series (MI-200/MI-J00) as BusMod, MegaMod or ComPAC products and for Maxi, Mini and Micro converters with VIPAC Arrays and VIPACs, which will facilitate discrete wire connections.

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If I am not using the Gate In, Gate Out, or Trim pins on VI-200 / VI-J00 converters and the PC, PR or SC on the Maxi, Mini and Micro converters, can I leave them floating?

This depends on how the converters are being applied; however, some applications do not require the functionality that these pins provide. Hence these pins can be left as a "no connect". See the Vicor Applications Manual and Maxi, Mini and Micro Design Guides for more information.

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Do I need filtering on the input and/or output side of the power converters?

All switching power supplies generate signals that could potentially interfere with other electronic circuits as a result of the switching action. Vicors quasi-resonant, zero-current-switching topology generates far less conducted and radiated noise than other topologies in both magnitude and frequency spectrum. EMI filtering can reduce the noise by an additional 40 60 dB. Depending upon your application, additional filtering may be needed to meet agency and/or load requirements. Some basic guidelines to follow for successful EMI filtering are:

• Keep current loops small. The ability of a conductor to couple energy by induction and radiation is proportional to the loop area.
• For conductor pairs, use wide (low Z) copper traces aligned above and below each other.
• Locate filters close to the source of interference; i.e., the power converter.
• Filter component values should be chosen with consideration to the desired frequency range of attenuation. For example, capacitors are self-resonant at some frequency, beyond which they look inductive.
• Keep bypass capacitor leads as short as possible.
• Bear in mind the proximity of noise sources to potentially susceptible circuits when locating components on the board.
• Contact Vicor applications engineering for assistance.

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How do I create a negative output?

Vicor power converters have isolated outputs so they can be referenced to a common node creating either positive or negative rails. To create a negative 5 V output for example, the +Out of the module would be connected to the common return (earth ground, chassis ground, etc). The -Out would then be treated as the "supply".

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Can the Three-Phase MegaPAC operate from a single-phase input?

The Three-Phase MegaPAC can be powered from a single-phase source as long as the input voltage is between 180  264 Vac. Although it is possible to connect the Line and Neutral wires to any of the J1 Line inputs, the most common wire scheme is listed below. For safety purposes, it is important to first verify that the input circuit is OFF, before handling any of the input wires. After confirming there is no input voltage on the wires, configure the J1 Input Power Connector as shown below.

J1-1 Line

J1-2 Neutral

J1-3 No Connect

J1-4 Earth Ground

Please refer to the Three-Phase / 4 kW MegaPAC Design Guide for information regarding single-phase power deratings.

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Why does the output power decrease if I trim the output voltage down?

Vicor power converters have a fixed output current limit. The output power rating divided by the rated output voltage (Po/Vo) is the rated output current (Io). Since the maximum current is fixed, a reduction in voltage reduces the output power. For example, a 5 V / 50 W module can deliver 10 A. If the converters output voltage is trimmed down to 2.5 V, the converter can still only deliver up to a 10 A maximum; therefore, the available maximum power is now 25 W.

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What is the switching frequency of your VI-200 / VI-J00 and Maxi, Mini and Micro converters?

Vicor VI-200 / VI-J00 and Maxi, Mini and Micro power converters use frequency modulated, quasi-resonant, zero-current switching in contrast to the pulse-width-modulated (PWM) switchers. As such, the operating frequency is both input line and output load dependant, and could range from under 100 kHz at light load, high line, to around 1 MHz at full load, low line. As a result, Vicors zero-current switching has much lower conducted and radiated noise levels than conventional pulse-width-modulation (PWM) converters, typically 20 40 dB lower.

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Do your modules load share?

Another aspect of the Vicor topology is that two or more power trains driven at the same frequency will inherently load share if their outputs are tied together. Load sharing is dynamic and guaranteed to be within a few percent. The VI-200 family has associated booster modules, VI-Bxx-xx (designated with the same input voltage range, output voltage and power level as the associated Driver, VI-2xx-xx). Booster modules may be slaved to a Driver, allowing construction of multi-Kilowatt arrays. Only a single connection is needed between converters with all converter outputs connected together; no trimming or adjustments are required to achieve load sharing. This is documented in more detail in the Vicor Applications Manual.

Vicors Maxi, Mini and Micro power converters have the capability of being configured in a fault-tolerant, power sharing "democratic" array. Maxi, Mini and Micro power converters can be configured into arrays in which each power converter naturally shares in the power delivered to the load. The arrays are inherently "democratic" in the sense that the "master" module (which provides synchronous control of the array) is automatically determined without any user intervention whatsoever. Furthermore, the array is inherently "N+M" fault tolerant: uninterrupted synchronous operation will continue despite any number of modules failing or being taken off-line, provided only that as the remaining modules in the array have sufficient aggregate power capability to support the load. Configuring the array is extremely simple, consisting of low voltage, capacitively coupled, connections between converter modules. For additional information regarding parallel operation of our Maxi, Mini and Micro converters, please see the Application Notes section of our web site.

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Do I need to fuse the input of the converter?

Safety agency conditions of acceptability require that the module (+) input terminal be fused and the baseplate of the converter be connected to earth ground. The location of the fuse must be in series with the positive (+) input lead. Fusing the negative input lead does not provide adequate protection as the PR and PC terminals of the Maxi, Mini and Micro converter (Gate In and Gate Out of the VI-200 / VI-J00 converters) are referenced to the Input. If a fuse located in the Input lead were to open, the PR and PC terminals (Gate In and Gate Out) would rise to the potential of the +Input. This could damage any converter or circuitry connected to these pins. The fuse should not be located in an area with a high ambient temperature, as this will lower the current carrying rating of the fuse.

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