Power Supplies frequently asked questions

Proper Output Loading Practices
Generally in multiple output power supplies, a Minimum Load (minimum current draw required for voltages to be in a specified range) is required on the main output to ensure regulation of the auxiliary outputs. Some multiple output supplies require a Minimum Load on all outputs. If unsure, a Minimum Load of 10% to 20% is a good rule of thumb. Although most single output power supplies do not have a Minimum Load requirement, in all cases, SnapTec recommends that you refer to the detailed specification sheets provided in downloadable PDF format on this web site.

Current Limit Characteristics
All of SnapTec's converters offer some form of Output Current Limiting; an output protection feature which limits the output current to a predetermined value in order to prevent damage to the power supply or the load under overload conditions. Some supplies are automatically restored to normal operation upon removal of the overload condition, and some require re-powering of the input. SnapTec recommends that you refer to the detailed specification sheets provided in downloadable PDF format on this web site. Forms of current limiting are:

Control Pin Operation
A number of SnapTec Power Supplies and DC/DC converters offer a Logic Level Inhibit operation where Logic "1" = On, and Logic "0" = Off. Most are designed to be operated by pulling the ON/OFF ("Control") Pin low (Minus Input or Output Return in some cases) to inhibit converter operation. If this function is not utilized, the Control pin may be left floating, as it is pulled high internally. SnapTec recommends that you refer to the detailed specification sheets provided in downloadable PDF format on this web site.

Series Operation
SnapTec power converters can be operated with the outputs connected in series. However, it is important to note some limitations:

Parallel Operation for Increased Power Output
Unless the power supply is specifically designed for parallel operation, parallel operation is not recommended. Two output voltages from fixed output converters will not be exactly equal. The converter with the higher output will try to provide the full load, causing it to go into current limit. The second supply will then do the same. Even if an adjust function is used to set the outputs, any drifts with time and temperature will cause the same reaction. SnapTec recommends that you refer to the detailed specification sheets provided in downloadable PDF format on this web site, or Contact our Technical Support department.

Parallel Operation for Redundancy
Connecting power converters in parallel for power redundancy is an acceptable practice. The converters must have their outputs connected in parallel through two diodes. Each converter must be capable of driving the full load. The diodes permit one output to fail without affecting the other.

The following illustration shows an example of connecting two SRA or SRC units in parallel. This configuration also applies to any other power supply or DC/DC converter.

Temperature Performance
All of SnapTec's converters are specified to operate within a given range of ambient or case temperatures expressed in °C. These are the temperatures that the supply may be utilized safely in, and perform to other posted specifications. Exceeding these temperatures diminishes the capability of the supply to deliver the full load current and may damage the supply. The "Derate Curve" section of the specification sheet illustrates how much power the supply can deliver outside its Full Load Operating Temperature Range. SnapTec recommends that "Derating" the power supply be considered in applications where the ambient temperature may exceed the recommended Full Load Operating Temperature Range. Other recommendations to consider are:

It is important to note that the Mean Time Between Failures (MTBF) will reduce sharply as ambient operational temperature increases. Dividing the MTBF by 2 for every 10 degrees Celsius over ambient is a a good rule of thumb.

Safety Agency Specifications
Underwriters Laboratories (UL) develops minimum safety standards for commercial electronic products in the U.S. Some states have made these standards legal requirements, though most are voluntary. UL does not "approve" equipment or systems, because this may be construed as a recommendation. Instead, it "recognizes" components and power supplies, and "lists" systems and end use equipment. The more common UL standard related to power supplies is, UL 1950 - Safety of Information Technology Equipment.

The Canadian Standards Association (CSA) is the governing safety standards organization in Canada, and compliance is mandatory. The CSA standard for electronic equipment (CSA 22.2) is very similar to UL 1950. Under agreement, UL 1950 references CSA 22.2 in its test reports, and CSA accepts UL's findings as compliant. Two of the more common CSA standards related to power supplies are:

The International Electromechanical Commission (IEC) is a group of technical committees from member countries, including the U.S., which based on consensus of opinion, publishes specifications for varying subjects. It is recommended that the National committees adopt these standards. The specification published by IEC of interest to power supply manufacturers is:

German Safety Laws are internationally recognized electrical standards highly regarded throughout Europe and the rest of the world. Both VDE and TUV are authorized to test and certify products to these standards. The common standard related to power supplies is:

Most of SnapTec products are certified to applicable UL, CSA, and IEC/TUV standards. SnapTec recommends that you refer to the detailed specification sheets provided in downloadable PDF format on this web site for standards information including file certification numbers.

Ripple and Noise
The level of AC voltage on the output of a power supply expressed in millivolts peak to peak at a specified band width. Ripple and Noise is dependent upon output voltage as specified per particular model. It is measured directly at the pins/screw terminals at nominal load, 25°C ambient, 0.1-uF bypass, peak to peak at 20 MHz bandwidth. SnapTec recommends that you refer to the detailed specification sheets provided in downloadable PDF format on this web site, or Contact our Technical Support department.

EMI and RFI
EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) are unwanted electromagnetic energy that pollutes the environment, and can effect the operation of other equipment around it. It can be radiated into the air, or conducted over system power lines. EMC (Electromagnetic Compatibility) is the ability of a system to function in a high EMI/RFI environment and the ability to limit its own EMI/RFI output. The International Special Committee on Radio Interference (CISPR) makes recommendations for EMI/RFI suppression to nationalized EMC regulatory bodies such as the Federal Communications Commission (FCC), and the German VDE. The FCC is the governing body in the U.S., and VDE is widely recognized in Europe as well as worldwide. SnapTec power supplies are designed to meet the EMC regulations directed by these governing bodies. We recommend that you refer to the detailed specification sheets provided in downloadable PDF format on this web site, or Contact our Technical Support department.

Input/Output Filtering
SnapTec products are designed for stand-alone operation per the posted specifications, and all filtering has been provided internally. If desired, it may be possible to add external components for the purpose of reducing Ripple, Noise, and EMI even further for example, where applications are ultra sensitive. Also, for example, where unclean line conditions may exist, or for reverse polarity input protection, recommendations may also be made for external circuitry that will accommodate such undesirable conditions. Ensure that the proper loading and measurement techniques are employed when testing and implementing power supplies before considering external components. Contact our Technical Support department for assistance.

Special Product Requests
In some instances, an application may require a specially designed power supply. This special product may be as simple as a slightly modified output voltage, or may require a totally custom design from "the ground up". SnapTec has developed and provides a wide variety of custom products to many of our customers. In some cases, one of these existing "specials" may meet your specific requirements. To better help us recommend the best product solution, we suggest that you fill out the Inquiry form within this site. Our design engineering group will review and respond immediately with a solution to meet your requirements. Or, if you prefer, give us a phone call on our sales line.

Warranty and Returns Policy
SnapTec products carry a 2-year warranty (from date of shipment) against defects in material or workmanship. SnapTec will repair or replace, at its sole discretion, any product returned and found to be defective. To assure proper handling and credit, all returned product must have a Returned Material Authorization (RMA) number. Please contact the office to obtain an RMA number prior to returning any product. Product returns without an RMA number will not be accepted. SnapTec is not responsible for products returned without an approved RMA number. The customer is responsible for return shipping charges, SnapTec will assume shipping charges for repaired/replaced products back to the customer. Product are not accepted for return once delivered to the customer.

Contacting Technical Support
SnapTec provide free technical support for all of our products. Our Technical Support team is available from 8:30AM to 5:00PM Sydney Time, or by Fax shown below. If you prefer, you may leave a detailed e-mail message and our Technical Support Team will respond within 24 hours. For more information on contacting SnapTec, please refer to SnapTec Home Page .

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