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This paper introduces components of rolling stock electronic equipment and different requirements for them, and puts forward key points complying with EN 50155 standards for selecting DC/DC Converter used in rolling stock electronic equipment, including isolation voltage, input voltage range, operating temperature range, EMC and so on.

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MOTIEN's converters include both through-hole and SMD components. This application note describes the soldering profiles for these two types of components and complies with the BS CECC 00802 and IPC/JEDEC J-STD-020 standards.

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Additional Capacitors at input and output can help reducing the ripple and noise. However too much capacitance at the output may cause the problem of start up of converter. It is recommended to use high grade Electrolytic capacitor with low E.S.R or Tantalum capacitors together with a small capacitance Multi-layer Ceramic Capacitor paralleled - which ca provide good filtering for ripple and noise.

The limit value for unregulated products are: 1W type 100uF, 2W types 220uF. For more detailed please see data sheets.

In unregulated DC-DC converter like our VA-2405S1 the output voltage will be affected by input voltage and output loading.That means it related with Load regulation and Line regulation.

For example, if under full loading, input voltage is reduced to 21.6V, the output voltage will be reduced to 4.4V highest.So under this condition the output voltage of 4.7Vdc or less happens.

But event the load is 65mA, approx 32% the output voltage goes down as 4.5Vdc also while the input voltage is too low. 

va-2405s1

MOTIEN's metal case has the stand-off at the bottom of case. Such unique design in metal cased DC-DC converter can actually help convect the heat generated from bottom of converter and bring a good heat sinking effect!

 

stand_off

Don't place another electrical component against the DC-DC converter. This will affect the heat sinking and cause electrical - magnetic interference which result in higher temperature and damage quickly. A recommended distance of 5.0mm min can avoid such problem!

 

5mm-01

Please see followed for differences between PWM and RCC type wide range converter listed below:

Differences PWM Type RCC Type
Switching Frequency Fixed Variable
Efficiency Higher Lower about 1~5% depend on models
Capacitive Load Lower Higher
Operating Temperature All models could support to 85°C Some models only to 71°C
Isolation Capacitor Needed No needed
Cost Normal Lower
Performance Stable Some models will have more noise under low input voltage!

 

 What is DC/DC converter?

A DC to DC Converter is a circuit which converts a source of direct current (DC) from one voltage level to another. In many applications, there is a need to convert one DC Voltage to another DC Voltage, either increasing or decreasing it. This is the role of a DC/DC Converter.
Among the various series of Motien’s standard products, we can sort out the products into following domains:

On Board & PC Board Mount DC/DC Converters-Isolated
Our isolated On-Board DC/DC Converters are designed to be soldered or mounted directly onto a PC Board. As a result, they can be mounted close to the circuit that needs the output of this converter. Resulting in low energy loss. They are offered in high grade molded encapsulated cases. Motien’s On Board dc to dc converter solutions range from 0.25 Watt to 40 Watts and the new higher output power products remain under developed.

Non-Isolated DC/DC Converters for POL (Point-of-Load) And LED drivers
Our Non-Isolated DC/DC Converters complement isolated dc/dc converters. The non-isolated dc/dc converters offer a smaller an less expensive solution. They are used to generate additional voltages not generated by the "bricks" at the point of load.
Housed in small size industry standard formats like SIPs, the more compact packaging provides significant space savings on the PC Board. Their compact size also allows the non-isolated dc/dc converters to be placed close to their loads = point of load. By placing dc/dc converters close to their load, we reduce power loss dissipated by heat on the board.


Providing a constant output current, Motien’s LED drivers are suitable for LED lighting. Compact size packages from DIL-14, DIL-16, DIL-24 to 2”X1” with various output current from 300mA up to 1A. Analogue/PWM Dimming and on/off control function equipped, bulk construction and boost construction provide input voltage range up to 57Vdc.
 

 Definition of specification

Efficiency : Efficiency is defined as :
Efficiency (%) = Output Power / Input Power X100 , efficiency is measured at full load and nominal line input.

Input Current
This is the typical input current that the converter will draw from the power source at nominal line voltage under full load and no load conditions.

Input Voltage Range
This is the minimum and maximum input voltage between which the converter will meet its specifications. The nominal value listed is the voltage used for all other tests unless otherwise specified.

Line Regulation
When the input voltage is changed from rated maximum to rated minimum while the outputs are at full load, the output voltage will also change. Line Regulation is the percent change in output voltage.

Load Regulation
When the output load changed from maximum rated current to minimum rated current, the output voltage changes. Load Regulation is the percentage in output voltage. For multiple output supplies each output is measured, while all loads are varied.

Noise
The output noise is specified at nominal line and full load. This specification is very difficult to measure correctly due to the measurement bandwidth (0~20MHz). Short leads and proper grounding techniques must be used. The output noise is specified in mV peak-to-peak. The majority of the noise reading due to the switching action of the converter and is at very high frequencies, whereas the peak-to-peak amplitude at the fundamental switching frequency is usually much less.

Rated Current
This is the rated load range for the output. Usually there is no minimum load required from proper operation, however some converters do specify a minimum load.(Such as our VB, R6,RD... Series) Operation below minimum load will not harm a Motien converter in any way, but load regulation or output ripple may suffer. Operation abobe the maximum rated load is not recommended as it may degrade specifications or the converter’s life. All Motien DC/DC converters are designed to be reliable in operation at the full rated load current provided that the case temperature does not exceed specifications.

Short Circuit Proteciton
Some Motien Converters are designed to withstand a direct short on the output pins and to recover to normal operation when the short is removed. Under some conditions, the long term life of the converter will be degraded unless the short is removed within a certain amount of time. For those simple Converters of Motien, unless special specified with short circuit protection, a direct short circuit on the output pins is prohibited.

Input to Output Capacitance
This is the isolation capacitance from the input pins to the output pins. This measurement is done with a 1kHz, 1V RMS capacitance bridge.

Isolation
This parameter is measured by applying the listed isolation voltage from the input pins to the output pins. The maximum allowable leakage under this condition is specified. Input or output to case isolation is also measured in the same way.

Case Operating Temperature Range
This is the temperature range at which the converter will operate with no derating. The case temperature is measured at the center of the top surface of the converter.

Storage Temperature
The storage temperature is the safe storage temperature for the device. Long term exposure to these temperatures should not degrade the converter’s performance.

Power Derating
This curve shows the expected performance of the converter in a large ambient and an infinite heat sink condition. The curve, showing still air performance, assumes that the converter and its load will not increase the ambient temperature. If the converter and its load increase the ambient temperature, a thermal runaway condition can occur. This curve is for preliminary design information only. The specifications are guaranteed over the case temperature range since Motien has no control over the application’s ambient environment.
 

 The understanding of Insulation

One major benefit of a DC/DC converter is to provide an isolated Power, but how can a small converter like V1-0505SSH6 provides a 6KVdc isolation and can this converter really withstand the high voltage? Can we put this converter across the isolation field where 5KVdc does exist directly??
Unless specified notification, most standard Motien standard DC/DC converter provide high galvanic isolation capability. However it’s recommended to check the application field before choosing the product with the suitable insulation grades. Please see followed for details.

Definition of Insulation

  1. Functional insulation is insulation needed for correct equipment operation. It does not protect against electric shock. Functional insulation would be used between parts having different potentials or between ELV or SELV circuits and grounded conductive parts. This type of insulation replaces operational insulation in the third edition of IEC 60950.
  2. Basic insulation provides basic protection against electric shock. This insulation is used between parts at hazardous voltages and a grounded conductive part or SELV part, between primary and the grounded screen or core of a primary power transformer, and as an element of double insulation.
  3. Supplementary insulation is independent insulation applied in addition to the basic insulation in order to reduce the risk of electric shock in the event of failure of the latter. Supplementary insulation is generally used between an accessible conductive part and a part that could become energized if the basic insulation failed or else as an element of double insulation. This insulation is required to ensure protection of the operator should basic insulation fail.
  4. Double insulation is composed of basic and supplementary insulation. It is used between an ungrounded conductive part or floating SELV circuit and a primary circuit
  5. Reinforced insulation is a single-insulation system that provides the same protection against electric shock as double insulation. Unlike basic or supplementary insulation materials, reinforced insulation may consist of layers of material that cannot themselves be tested singly.

In summary, basic and supplementary types of insulation each consist of a single layer, double insulation involves two layers, and reinforced insulation is a single layer that is equivalent to two layers of insulation. Table I charts the different types of insulation required between pairs of device components.
Device Areas Basic Reinforced Suppliementary Funional
 Primary winding to primary winding       x
 Primary winding to grounded screen x      
 Primary winding to insulated body x      
 Primary winding to double-insulated body   x    
 Primary winding to hazardous secondary x      
 Primary winding to ELV or grounded SELV x      
 Primary winding to ungrounded SELV   x    
 Grounded screen to insulated body       x
 Grounded screen to double-insulated body       x
 Grounded screen to hazardous secondary x      
 Grounded screen to ELV or SELV       x
 Double insulation to double-insulated body       x
 Double insulation to hazardous secondary   x    
 Double insulation to ELV     x  
 Double insulation to SELV       x
 Hazardous secondary to ELV x      
 Hazardous secondary to grounded SELV x      
 Hazardous secondary to ungrounded SELV   x    
 ELV to grounded SELV       x
 Grounded SELV to ungrounded SELV       x
 TNV to primary   x    
 TNV to grounded or ungrounded SELV x      
 TNV to ELV     x  
 TNV to grounded hazardous secondary   x    
 TNV to ungrounded hazardous secondary   x x  

Table I. Types of insulation required between device areas: B = basic, R = reinforced, S = supplementary, and F = functional.

The Concepts in Application
To determine the required creepage distance and clearance spacings for an electronic product, the best method is to first draw a block diagram of the design (see Figure 2) from which a table of the required spacings can be prepared (see Table II). For example, the primary section of a power supply is treated as a block. Spacings are examined between hot and neutral to ground and between all primary and secondary parts. Each circuit should be regarded as a block.

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Figure 2. A block diagram of the electronic device for which the spacing requirements in Table II have been calculated.

It is important to note that the voltages of each block are not added together if they are powered from the same source (i.e., across a transformer). In the case of a relay contact where the contacts are connected to a different source, the two voltages are added together to determine the working voltage.

Location in System Insulation Type Maximum Working Voltage(Vac) Required Creepage Distance Required Clearance (mm) Test Voltage
(Vac)
mm CTI Value
A Basic 230 2.5 175 2.0 1500
B Double 260 6.4 175 4.0 3000
C Basic 460* 6.3 175 3.2 1674
D Basic 460* 6.3 175 3.2 1674
E Double 260 6.4 175 4.0 3000
F Double 260 6.4 175 4.0 3000
G Basic 230 2.5 175 2.0 1500
H Basic 230 2.5 175 2.0 1500
I Basic 460* 6.3 175 3.2 1674
J Functional 230 2.5 175 1.5 1500

 *Working voltage based on the rating of the relay contact plus 230V.

Table II. Tabulation of creepage and clearance distances required for the system diagrammed in Figure 2, which is characterized by Pollution Degree 2 and Overvoltage Category II. Insulation types are basic (B), double (D), and functional (F). Source: Tables 2L and 2H of IEC 60950.

Motien Technology’s most standard DC/DC converters are designed to have Functional Insulation, unless with other specified notes. For requirements of insulation and isolation, please check with us in advance.
 

 Case temperature and safe operation

We can see all the time in the specifications two different items: operating temperature and maximum case temperature, so which one defines the real performance of this device?

  • Operating temperature range defines the temperature range which the converter can operate normally, and maximum case temperature defines the allowable maximum temperature by the case of the converter.

  • When the device is working over the maximum case temperature, despite the environment temperature is still within the range of operating temperature, the forced heat sinking (air convection or other effective approaches) is absolutely required. The case temperature comes from environmental temperature and internal temperature rise. Over high case temperature damages the internal parts of converter and reduce the lifetime.

  • Derating: When choosing converters, it’s a must to take into account the actual needs of the operating temperature range. Different temperature level use different materials and processes, so prices vary greatly. There are two choosing method: One is based on the use of power and package, if the use of power are close to the actual rated power, then the nominal temperature range modules must strictly meet the actual needs with even a slight margin. Second, choose in accordance to the temperature range. If a smaller temperature range is chosen as a result of considering the cost, but the temperature approaches now and then the limits of the situation, what should we do? Derating operation. Choose higher power or greater package products, to lower the temperature rise. Thus can be alleviated this contradiction to some extent. Derating ratio of different grades vary with the power, generally is 3~10W/°C above 50W. In short, choice of wide temperature range, the power can be used more fully and smaller package, but higher prices; choice of temperature range or products, lower prices, larger power margin and package.

  • Safe operation: General recommendations of the actual use of power is 30~80% rated power of the converter. Too less loads lead to waste, too high loads will produce too much heat and are relatively not so stable. A waste of resources to load too light, too heavy on the temperature rise, the negative reliability. Some Motien products with higher output power usually provide 120 to 150% bearing, but it is not recommended to work long hours under the over load conditions. After all, this is only a short-term protection measuring.

  • Keeping a good space and convection for air-circulation is highly recommended.
 

 Ripple & Noise and Input filter…

  • Ripple & Noise - Every single Motien product had been tested thoroughly before leaving factory, especially the output ripple and noise. Unless other special requirement, there’s no extra output capacitors required to help reduce the output ripple and noise. It’s highly recommended to use high grade electrolytic capacitor with low E.S.R. or Multi-layer capacitor. However the grand total of output capacitance is thus a must to check. With a large output capacitance when switching on, there’s no charge on the capacitors and the DC/DC converter immediately experiences a current can be so large as exceeding the ability of the converter and the converter can go into current limit or an undefined mode of operation. In the worst case, the converter continuously oscillates as it keeps trying to start, go into overload shutdown and then retries again. The DC-DC converter may not survive if this condition persists. Please check carefully the recommended maximum capacitance load. When fighting with the issue of ripple and noise, an additional input filter (with LC filter or Pi filter) in front of the input side maybe more helpful than having a large output capacitor.

  • EMC- For those Series with CE verification, Motien would have the products verified with EMC… Mostly these products were tested and verified with the norm of EN55022 class A:
    • Please understand, the EMC information verifies only the converter itself, user can be sure that the device has been verified with the immunity and emission of EMC issues. Regarding how the EMC issue of the whole application, this is out of the range Motien can handle.
    • Having LC filter or Pi filter in front of the converter may help improving some EMC issue in the application. For application where high magnetic field, surge or noisy interference exists, user has to consider about the possible damage coming from the input power source and interference. It’s welcomed to have all the possible interference from customer to help solve the issue of the worse application environment.
 

 How to choose the right converter?

Step 1. Is isolation required? (An isolated converter has outputs that are floating and not connected to the inputs which are isolated and galvanic.) No isolation needed: Check our VR series first.
Isolation needed: check the application for which kind of insulation grade to have. (Refer to 3. Understanding of insulation or contact your Motien dealer or write us : sales@motien.com.tw)

Step 2. Decide on the output voltage and number of outputs : single, dual bipolar(+/-), dual isolated or triple. It is also important to decide whether the output voltage needs to be regulated or unregulated. Unregulated converters are offered standard without short circuit protection or optionally with short circuit protection. (option-P beside the series name, e.g. V1P)
All series are available with single outputs. Please note that a dual output converter can be used as a single output by leaving the common pin unconnected. E.g. +/-5=10V, +/-12V=24V, +/-15V=30V…etc.

Step 3. Decide on the output current. The output voltage times the output current gives the output power of the converter in Watts. DC/DC converters are designed to run at full load, so only round up the power if a suitable converter is not available. E.g. 5V @ 150mA = 0.75W= 1W converter
                          E.g. +/-15V @ +/- 1A = 30W = 30W converter

Step 4. Decide on the input voltage. Standard input voltage ranges are:
             3.3, 5, 9, 12, 15 ,24VDC with +/-10% tolerance
             4.5~9V, 9~18V, 18~36V, 36~72VDC with 2:1 input voltage range
             9~36V, 18~72VDC with 4:1 Input voltage range.

Step 5. Understanding performance limit of products:

  • When choosing small power products, please check the actual changing ratio of input voltage and output loading, most small power products like V1, V3, VA, VE series are unregulated, the output voltage changes upon input voltage and output loading. If the input voltage changes over 10%, choosing wide input products like VB, VBW, RBW series is recommended. If it’s only the load changing, simply choose the M1 series with semi regulated output or V4, M4, V5, VF series can overcome the issue from load changing.
  • Regulated output series like V4, V5, M4, VF series use a high efficiency passive regulator at the output, upon the characteristic of passive regulator, the input no load consumption will be a consideration in those application which is battery powered base equipment.
  • When choosing Pulse Frequency Modulation construction products like VB, R6, RD, RJ, RK series, the power supply should be considered to have more ratings to undertake the transient current during the start up stage. In some application this transient current maybe higher than 1A. For those power supplies with précised over load protection or limited output current, such high current may disturb the power rise up.
  • When choosing Pulse Width Modulation (PWM) construction series (most wide range products of Motien like V6,V7,V8,V9,VD,VG,VJ,VK,VM,VN…), under the consideration of over load protection, a maximum capacitive load is provided and limited. An application with over capacitive load caused the trouble of start up.
  • For products specified “short circuit protection”, a short at the output is acceptable. However, to provide a protection during the abnormal operation, a fuse is thus recommended to be settled at the input of the converter. This is to avoid when the overload happens, such converters keep operating and draw a high input current and burn the converter itself and other components.
  • Carefully checking the working voltage come across the input and output, if there’s additional request of insulation, please check with us for the required insulation. For medical equipments, train, nuclear power, aerial space equipments where higher grade insulation is required, it has possibility to harm human body and life directly by wrong operation and damage. Don't hesitate to consult us.
  • The calculation of AC (rms) = DC /1.414 is NOT applicable when proceeding a withstanding voltage! It’s understood that we usually use root mean square to stand for an AC voltage. But when proceeding an Input/output withstanding voltage test (usually called Hipot test), it’s definitely forbidden to apply the AC value from the above formula. The actual applied voltage of AC is actually nearly double of DC è AC(rms)/0.707 = AC (peak), AC(peak) X2 = AC peak to peak, the actual amplitude of applied AC voltage should be the value of peak to peak. In most cases, without a reinforced insulation, the insulator there between input and output will be destroyed by this high voltage.

 

If you can not find a solution in the RAQ, please feel free to contact us or call +886-6-384 2366 (Rep.), Thank you!

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