Question 1

What is the switching frequency of the CSS Series (CSS65/CSS65A/CSS150CSS500)?

Accepted Answer

A. The CSS65 has a switching frequency of 63kHz.
The CSS65A has a variable frequency of between 48kHz and 68kHz at full load 115V-230VAC input.
The CSS150 has a variable switching frequency depending on load. (Figure 1)
The CSS500 has a switching frequency of 90 to 100kHz.

Figure 1

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Question 2

What is the overload characteristic of the CSS500?

Accepted Answer

A. The CSS500 overload protection is hiccup mode and attempt to restart once per second.

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Question 3

I don't want to stop the system&#44 so I would like to operate it redundantly (backup). Is this possible? Also&#44 what should I be cautious of when using remote sensing during redundant operation?

Accepted Answer

A. Redundant (backup) operation is possible.

Please match the diode to the output side and then connect.
If there is a remote sensing terminal, please be sure to perform sensing on the anode side of the diode.
If sensing is performed on the cathode side of the diode, the power source operation may become unstable.

Please use the following guidelines when selecting a diode:
(1) The repetitive peak reverse voltage is more than twice the rated output voltage of the power supply
(2) The average output current is more than the rated output current of the power supply
(3) Diode with forward voltage that is as low as possible (Example: Schottky diode)
Furthermore, if the diode is used alone, the element may be damaged by heat. Therefore, be careful when using a radiator, etc., for cooling and confirm that the element temperature is within the range specified by the manufacturer. *Please use the backflow prevention module RP-60-20 or other TDK Lambda products.

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Question 4

Can I engage in parallel operation of power sources with different specifications such as output voltage&#44 power&#44 etc.?

Accepted Answer

A. Please refrain from parallel operation with different models. Doing so will create an unbalanced load current, exceed the rated current, and result in failure.
When engaging in parallel operation, use the same model which supports parallel operation.

To determine the feasibility of parallel operation, please check the Parallel Operation section in the specifications on the technical data page of each product on the product information website (TDK Product Center). Use is possible if there is a description such as "Possible." However, use is not possible if a "-" is listed or if no item is listed.

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Question 5

What should I be cautious of when connecting multiple units in series?

Accepted Answer

A. When connecting multiple units in series, high voltage is applied between the power supply output (secondary side) and the FG. Therefore, it is necessary to consider isolation between the power supply output and the FG.
Based on consideration of customer equipment, basic isolation is required between the power supply output and the FG.
Furthermore, if there is an SELV (ES1 in 62368-1) part in customer equipment, reinforced isolation is required between the SELV (ES1 in 62368-1) and the power source output. Also, reinforced/double isolation may be necessary for the output line.
Additionally, if the output voltage exceeds 60V DC, which is the upper limit of the SELV (ES1 for 62368-1) target range, it is also necessary to prevent the electric shock which will result when touching the human body, etc.
Also, the output voltage in series operation and the withstand voltage for the required isolation change depending on the conditions of customer equipment.
Please contact TDK-Lambda for details.
TDK-Lambda products are designed with SELV (ES1 of 62368-1) and the target range is 60V DC or less.
If the power supply outputs are connected in series that does not exceed SELV (ES1 in 62368-1), the safety standards for a "single power unit" take effect.

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Question 6

During capacitive load connection&#44 a surge current that exceeds the rating flows on the output side. Can I use it?

Accepted Answer

A. If the surge current flows for only a few milliseconds and has a low frequency (for example, a few times per day), it does not affect the component temperature and use is possible.
Please avoid use in an environment where repeated surge currents flow may cause the temperature of the parts to rise.
When selecting the power source, please consider the drooping characteristics of overcurrent protection and the starting characteristics of the load side. 　

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Question 7

Can I connect products with different capacities in a series?

Accepted Answer

A. It is possible to connect products with different capacities in a series.
However, please use a load current within the range of the model with the smallest maximum output current.

Example) Operation of a 63V output voltage stack series consisting of (1) 150W-48V output model and (2) 50W-15V output model
(1) 150W-48V output model: Output voltage = 48V, Output current = 3.3A (100%)
(2) 50W-15V output model: Output voltage = 15V, Output current = 3.5A (100%)

The maximum load current of the maximum output current for the (1) 150W-48V output model and the (2) 50W-15V output model is 3.3A and 3.5A respectively, so the upper limit of the load current is 3.3A, which is the smaller of the two models (150W-48V output model).

TDK-Lambda products use SELV (ES1 in 62368-1): It is designed with a special low voltage circuit as a safety feature, and is intended for circuits with a DC of 60V or less. The above usage example of series operation exceeds the safety voltage (peak value 42.4V, DC 60V), so the obtained safety standard is invalid. In this case, there are other important points which must be considered. Please contact TDK Lambda.
If the power supply outputs are connected in series that does not exceed SELV (ES1 in 62368-1), the safety standards for a "single power unit" take effect.

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Question 8

I would like to select a breaker. What are the different times for inrush current flow?

Accepted Answer

A. The inrush current varies depending on the model.
For the inrush current waveform, see the section on "Input Surge Current (Inrush Current) Characteristics" in the model data on the technical data page of each product on the product information website (TDK Product Center).

Depending on the performance characteristics of the breaker, this inrush current may trip a breaker.
Breaker characteristics: Before selecting a breaker, check the section entitled "Operating Time Against Current Ratio" to confirm that it is outside the operating range of the breaker.
Breaker types suitable for the switching power supply are low-speed breakers or delay breakers, which are resistant to being tripped by pulse current.
Moreover, please perform an evaluation using the device.

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Question 9

There seem to be several types of overcurrent protection characteristics. What are the differences?

Accepted Answer

A.There are three main types: Constant-current voltage droop, F-shaped droop, and Intermittent.

Constant-Current Voltage Droop Type
When the output current reaches the overcurrent detection value, the voltage will drop while maintaining the current.
If the output current drops below the overcurrent detection value, the output voltage will automatically recover.

Foldback Drooping Type
When the output current exceeds the overcurrent detection value, both output voltage and current will drop.
Output may not automatically recover in this mode, so input must be turned on again in such a case.

Intermittent Type
When the output current reaches the overcurrent detection value, both the output voltage and current will periodically repeat pulse operation.
If the output current drops below the overcurrent detection value, the output voltage will automatically recover.

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Question 10

Is square wave input possible?

Accepted Answer

A.The input of the switching power supply is assumed to be a sine wave, and a square wave is not guaranteed.
A sine wave is recommended for the input.
The main concerns for square wave input are as follows:
1) Products with internal harmonic current suppression (power factor correction) circuits adjust input current in response to sudden changes in input voltage, which may result in excessive current flow.
2) Sudden changes in input voltage may cause a buzzing sound from the input filter of the power supply.

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Question 11

What are the risks of not using the FG connection?

Accepted Answer

A.The FG terminal of the power supply should be connected to the equipment’s ground terminal for safety and noise reduction.
If not grounded, the following may occur:
・The equipment is not in compliance with safety standards.
・Risk of electric shock.
・It may affect EMC and other product specifications.

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Question 12

Is it safe to ground the output on one side?

Accepted Answer

A.Basically, it won’t cause a problem with the operation of the power supply, but there is a possibility that the output ripple may worsen and EMC standards may not be met.
Therefore, please evaluate the product thoroughly before use. The insulation withstand voltage specification is eliminated, and the insulation withstand voltage between input and output is the same as that between input and FG.

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Question 13

Is it possible to connect each phase of the three-phase AC to three single-phase input power supplies?

Accepted Answer

A.Even if a single-phase is drawn from a three-phase, it will still work as a power source.
However, it is recommended that the same power be used for each phase.
For power supplies with fuses mounted only in the L phase, insert a fuse in the N phase of each power supply and wire the power supply so that either the L or N phase of the power supply will always blow.

Both Δ-connection and Y-connection can be used, but in the case of Y-connection, the line-to-line voltage is √3 times the phase voltage, so be sure not to exceed the input voltage range of the power supply.
Therefore, do not exceed the input voltage range of the power supply.

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Question 14

How long does it take for the overcurrent protection circuit to operate?

Accepted Answer

A.The operating time is not specified because it varies depending on each product and the conditions under which the protection circuit operates.
When an overcurrent is detected, the overcurrent protection circuit inside the power supply operates instantly (tens to hundreds of microseconds).
Note that if a large capacitor is connected on the load side, there may be a delay until the protection circuit operates and the output voltage drops.

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