Terms and Conditions

Frequently Asked Questions

1. The power supply outputs are not regulated, is the power supply bad?
Response: Do you have the system loaded? If not the customer should apply a resistive or active load to the system. The load should be 10% greater of the power supply's main output (V1).

2. Is the reset switch debounced?
Response: The reset switch is not debounced, but does have an open collect output, which will set the System Reset bus low, as long as the button is fully actuated.

4. Rise time is too long.
Response: Usually this is caused by the auto-ranging circuit. This circuit can be disconnected and the power supply hard wired for 115vac or 220vac.

5. The power supply is ticking, is there a problem?
Response: If the customer is using a two-phase source and an auto-ranging power supply is used, then the power supply can be hard wired for 115vac or 220vac to rid the system of the noise

Power Terms

Bandwidth: A range of frequencies over which a certain phenomenon is to be considered.

Bleeder Resistor: A resistor added to a circuit for the purpose of providing a small current drain, usually to provide a load for improving output voltage stability, or to assure discharge of capacitors.

Cross Regulation: The effect of a load change on one output to the regulations of another output. It usually only applies to non-post regulated (quasi) outputs.

Crowbar: An over-voltage protection method which shorts the power supply output to ground in order to protect the load when an over voltage fault is detected.

Current Sharing: Equal division of the total load current between two or more power supplies. Effeciency: The ratio of output power to input power.

Floating Output: An output of power supply that is not connected or referenced to any other output usually denotes full galvanic isolation. They generally can be used as either positive or negative outputs. Non-floating outputs share a common return line, and are hence DC referenced to one another.

Ground Loop: An unintentionally induced feedback loop caused by two or more circuits sharing a common electrical ground.

Holdup Time: The length of time a power supply can operate in regulation after failure of the AC input.

Inrush Current: The peak current flowing into a power supply the instant AC power supply is applied. This peak is usually much higher than the steady state input current, due to the charging of the input capacitors.

Leakage Current: Relating to current flowing between the AC supply and earth ground. The term does not necessarily denote a fault condition. In power supplies, leakage current usually refers to the 60Hz current, which flows through the EMI filter capacitors, which are connected between the AC lines and ground (Y caps).

Line Regulation: The change in output voltage when the AC input voltage is changed from minimum to maximum specified.

Load Regulation: The change in output voltage when the load on output is varied.

Local Sensing: Using the voltage output terminals of the power supply as sense points for the voltage regulation.

Magnetic Amplifier (Mag Amp): A saturating inductor, which is placed in series with power supply output for regulation purposes.

Margining: Adjusting a power supply output voltage up or down from its nominal setting in order to verify system performance margin with respect to supply voltage. This is usually done electrically by a system-generated control signal.

Minimum Load: The minimum load (current/power) that must be drawn from the power supply in order for the supply to meet its performance specifications.

Over Current Protection (OCP): A circuit which limits the maximum current provided by the power supply outputs. Sometimes referred to as "Over Load Protection". There are two types:

Foldback current limiting; The output voltage remains constant and within specified limits up to a critical current, which is 5-25% greater than full-rated current. At which point, both the voltage will drop off and the current will go into a short circuit condition. The output will shut down, and automatically restart once the problem has been removed.
Straight line current limit; As output current is increased to Ic (critical current), the output voltage will drop to zero, at which point the output fall into a short circuit condition. The output will shutdown, and automatically restart once the problem has been removed.

Over Shoot: A transient output voltage change which exceeds the high limit of the voltage accuracy specification and is caused by turning the power supply on or off, or abruptly changing line or load conditions.

Over Voltage Protection (OVP): A circuit which either shuts down the power or crowbars the output in the event of an over voltage condition.

PARD: Periodic and random deviation, referring to the sum of all ripple and noise components on the DC output of a power supply, regardless of nature or source.

Post Regulator: A secondary regulating circuit on an auxiliary output of a power supply to provide full regulation on that output.

Power Factor: The ratio of true power to apparent power in an AC circuit.

Regulation: The ability of a power supply to maintain an output voltage within a specified tolerance as referenced to changing conditions of input voltage and/or load.

Reverse Voltage Protection: A circuit that prevents the power supply from being damaged in the event that a reverse voltage is applied at the input or output terminals.

Remote Sense: Wires connected in parallel with power supply output cables such that the power supply can sense the actual voltage at the load to compensate for voltage drops in the output cables and/or devices.

Ripple: The amplitude of the AC component on the DC output of a power supply usually expressed in millivolts peak to peak or RMS. For a linear power it is usually the frequency of the AC mains. For a switching power supply, it is usually the switching frequency of the boost / converter stage.

Rise Time: The amount of time for a power supply to achieve regulated outputs from turn-on. Usually measured from 10 to 90% of the nominal rating for the output.

Soft Start: A technique for limiting input current to the power supply. Most commonly utilizing a thermistor in series with the input.

 Current SHARING CONFIGURATIONS FOR PSUs

There are several methods used to split the power load between power supplies. Not one method is best for all applications or customers. What Elma can offer is options for the customer to choose from, or the Engineering Department can make suggestions based upon the customer's requirements. Following are the methods, and the descriptions of their use.

Load Share: This configuration is used for two reasons:

1) High power applications, where one power supply cannot provide the power for the entire load.
2) Limited space, where one large power supply will not fit. Which forces the use of two smaller power supplies.

 

Method:
a) Third Wire Current Share; Power supplies are purchased with this option. A wire is used for communications between the two power supplies or more. The advantage is 50/50 current share within 1%. For this application, I would suggest nothing else.

N+1 Redundancy: This configuration is used for fault tolerant systems, where a customer cannot afford down time. All methods shall use isolation diodes.

Method:
a) Pre-load resistor; Power resistors are used before the diodes to force the power supply to maintain regulation. Typical current share is at 10/90. This could be a problem for heavy load applications.
b) Third wire current share; Same as method for Load Share, except with diodes.
c) Program Slope (Droop); Using standard power supplies off the shelf, and adding resistors in series with the positive sense lead on the power supply. Current share is typically 60/40.

 Technical Data:
Current Carrying Capacity of Copper Conductors

Current carrying capacity is defined as the amperage a conductor can carry before meeting either the conductor or the insulation. Heat, caused by an electrical current flowing through a conductor, will determine the amount of current a wire will handle. Theoretically, the amount of current that can be passed through a single bare copper wire can be increased until the heat generated reaches the melting temperature of the copper.

There are many factors which will limit the amount of current that can be passed through a wire. These major determining factors are:

Conductor Size: The larger the circular mil area, the greater the current capacity. The amount of heat generated should never exceed the maximum temperature rating of the insulation.

Ambient Temperature: The higher the ambient temperature, the less heat required to reach the maximum temperature rating of the insulation.

Conductor Number: Heat dissipation is lessened as the number of individually insulated conductors, bundled together, is increased.

Installation Conductors: Restricting the heat dissipation by installing the conductors in conduit, duct, trays or raceways lessens the current carrying capacity. This restriction can be alleviated somewhat by using proper ventilation methods, forced air cooling, forced air cooling, etc.

Taking into account all the variables involved, no simple chart of current ratings can be developed and used as the final word when designing a system where amperage ratings can become critical.

The chart shows current required to raise temperature of single insulated conductor in free air (30°C ambient) to the limits of various insulation types. The following table gives a derating factor to be used when the conductors are bundled. These charts should only be used as a guide when attempting to establish current ratings on conductor and cable.

Amperes