REC20K-Z Series

Although some of our DC/DC converters contain Class A or Class B EMC filters built in, many of our low cost DC/DC converters contain only simple input filters. The customer can then decide to add an EMC filter individually or for all of the converters together to save costs. External EMI filter suggestions are given in our Application Notes for both Class A and Class B levels. All of our AC/DC converters contain a built-in Class B EMC filter as standard.

The UKCA (UK Conformity Assessed) marking is a new UK product marking that is used for products being placed on the market in Great Britain (England, Wales and Scotland). It applies to the same products that are currently CE marked. The circumstances in which self-declaration of conformity for UKCA marking can be used are the same as for CE marking. Based on current UK rules, RECOM is eligible to self-declare for the UKCA Declaration of Conformity (DoC) as long as the EU and UK regulations remain aligned.
RECOM will make available a separate UKCA Declaration of Conformity (DoC) based on the existing CE Declaration of Conformity (DoC) and test reports (self-declaration). CE marking remains valid for goods placed on the market in Great Britain until 1 January 2023. The UKCA marking must be used for placing goods on the market in Great Britain after this date. RECOM will continue to actively monitor any changes to the UKCA rules based on UK government guidance and react accordingly.
We will also instigate a program to successively add the UKCA mark to our CE marked products to fulfil our obligations as manufacturer. For further information or enquiries regarding our UKCA policy, contact TechSupport

RECOM prides itself on having a comprehensive certification portfolio, with full third party UL/IEC/EN certifications (not just 'designed to meet'). Certifications cover Industrial, Medical, LED lighting, Household, Railway and Automotive standards, depending on the application area of the converter.

We provide many medical grade converters with UL/IEC/ EN-60601-1 certifications (3rd Ed.), including risk assessment documentation.

Refer to the instructions given by the conformal coating supplier regarding the recommended process for washing and drying the boards before applying the conformal coating. We have never received any complaints of chemical incompatibility or any other problems with conformal coating our products.

Ultrasonically cleaning can cause damage to sensitive electronic components, so it is not recommended. Nevertheless, some RECOM parts can be cleaned without harm, so if ultrasonic cleaning is necessary, please contact Recom Technical Support for advice.

All RECOM production batches are burn-in tested in our factory before being shipped to the customer.

The inrush current is dependent on the converter, the load (especially the capacitive load) and the impedance of the primary power supply. Therefore, there is no recommended value for the inrush limiting inductor as this need to be individually worked out for each application. Having said that, usually 22µH~100µH is a good starting point.
A CMC is a good inrush current limiter because the core does not go into saturation with high currents (the +ve inrush current is balanced out by the -ve inrush current), so it has a dual purpose: EMC filter and inrush limiting. However, for high power converters it is sometimes better to use a low inductance, high current, choke that is selected to reduce inrush rather than a high inductance choke selected for the best EMC filtering because otherwise too much power could be lost through the choke's resistance during normal operation.

Recom does not offer this feature in any of its DC/DC converters. Synchronizing the oscillators in several converters is a useful technique where beat frequencies must be avoided at the cost of an increased amount of interference at the main frequency. Usually effective results can be achieved by individually filtering each converter without creating a strongly interfering main frequency.

In theory, yes, but in practice it is very non-linear. Adjusting the output voltage using an external voltage or current can also affect the regulation and short circuit behaviour, so it is not recommended.

Our AC/DC converters usually incorporate input surge protection, although some series require an external suppression MOV to meet all operating conditions. Our DC/DC converters do not usually incorporate surge protection, although an electrolytic capacitor placed close to the input pins is usually sufficient to meet the requirements of 61000-4-5.

Reverse polarity protection is not built inside any of the converters. It needs to be added externally. We recommend adding an external MOSFET for higher power converters or a simple blocking diode for lower power, non-critical applications.

RECOM has one of the largest selection of non-isolated DC/DC products on the market. Our search engine allows searches for non-isolated converters only.

An isolated DC/DC converter has no electrical connection between the input and output. So it does not matter if Vin+ is connected to a positive supply and Vin- is connected to ground or if Vin+ was connected to ground and Vin- was connected to a negative supply. This is useful in the telecommunications industry, for example, where a standard -48V supply can be used to generate a +5V output (Vin+ = ground, Vin- = -48V, Vout + = 5V, Vout- = ground).
This does not apply to non-isolated switching regulators, but the R-78 series can be configured to generate a negative output voltage from a positive input voltage (refer to the Application Notes).

The main problem with a 12 battery as a power source is that it can deliver very high inrush currents. Normally with lower power converters (under 20W), this is not a problem, but for the higher power converters the inrush current can damage the converters or extzernal components. The other issue with batteries is if the end-user connects the battery the wrong way around, this will instantly destroy any converter. To avoid these problems, an external blocking diode or FET can be fitted and either a soft-start circuit or an inrush current filter can be added. Please contact Recom Technical Support for suggested circuits and component values.

The unregulated converters have a deviation curve depending on the load. The lower the load is, the higher the output voltage. Please check the graphs included in our Datasheets about Deviation/Load. Usually, these converters need at least 20% load.

RECOM prides itself on having comprehensive datasheets, but there may be a parameter or operating characteristic that it not listed.

We offer local Technical Support through our offices in Austria, Germany, USA, Singapore, Japan and China, or you can contact your local RECOM contact or distributor to ask us for more information.

The converters have a derating curve that starts usually between 70°C and 85°C. From that temperature point onwards the load must be reduced to limit the internal heat dissipation. You can use a heat sink to move this temperature point up a few degrees, but if your application doesn’t have an adequate cooling system, even a large heat sink may not be effective. Plastic cased converters cannot be effectively heatsinked. Use a higher power converter instead to increase the derating.

You can use a dual 15V output converter (+/-15V), omitting the common pin and using only the +Vout pin and –Vout pins. Dual output converters regulate between the +ve and –ve output rails only, so connection to the common pin is unnecessary for the converter to work normally. This is true of any dual output converter, so +/-5V = 10V, +/-9V = 18V, +/-12V = 24V and +/-15V = 30V.

If isolation is not required, the –ve output pin can be connected back to the +ve input pin to boost a supply voltage. For example, a 24V supply feeding an isolated 24Vin, 24V out DC/DC converter wired up this way will generate a 48V output voltage with double the power: 24V@1A (24W) from the supply + 24V@1A (24W) from the converter = 48V@1A (48W)

The Remote On/Off or Control pin is commonly used for the following reasons:
To control a high-power converter using a low-power signal. The input power of a control pin is typically only a few milliwatts, but it can enable or disable a converter of as much as a hundred watts. This means that the low power output of a microcontroller or logic IC can be used to control a system without the need of extra amplifiers or bulky relays.
To power-up or power-down a system of several converters in the right sequence. Many complex power supplies need to start up or shut down in a certain order to be safe. An example could be a computer-based controller where the microprocessor should be up and running before the peripherals are powered up. Another example is where one power supply feeds another. The primary power supply often should have reached a stable output voltage before the secondary power supplies are turned on.
To save energy. A control pin can be used to turn off the power completely to parts of a circuit during standby mode, while leaving a central watchdog circuit still active. This is especially important for battery powered circuits because all DC/DC converters draw some power even when they are not loaded.
To reduce the inrush current. In a system of several parallel sub-systems, it is often useful to stagger the start-up of each sub-system so as not to overload the primary power supply or cause the main fuse to trip or blow on switch-on.

The trim pin (if fitted) can be used to increase or decrease the regulated output voltage over a limited range (typically +/-10% or -20%, +10%). Some switching regulators offer a Vadj. pin which can adjust the output voltage over a wider range (up to +/-50%).
Connecting a resistor between trim (or Vadj,) and the Vout+ pin will reduce the output voltage. Connecting a resistor between trim (or Vadj,) and the Vout- or Gnd pin will increase the output voltage.
Trimming is typically used to help compensate for the voltage drop along a long cable or PCB track by increasing the output voltage, or to reduce the output voltage to avoid over-voltage stress on the load under worst-case conditions.
Voltage trim is also useful to match different battery chemistries. A 12V lead acid battery can be trickle charged using a 12V converter trimmed up to 13.2V (+10%) or a LiPo Battery safely charged from a 5V converter trimmed down to 4.6V (-8%).

The sense pins (Sense + and Sense-) are used by the DC/DC converter to regulate the output voltage as delivered to the load, not as measuresd directly across the output pins. The converter uses four connections, Vout+ and Vout- delivering a high current and two low current connections, Sense+ and Sense- for feedback. The advantage of using the sense pins compared with simply trimming up the output voltage to compensate for the volt-drop along the connection is that sense pins regulate the load voltage at both low and high load currents, thus avoiding too high a load voltage when lightly loaded. Sense pins can also be used by some load sharing controllers to allow two or more DC/DC converters to be connected in parallel to increase the power.

Some unregulated bipolar converters feature power sharing, where all or some of the load can be taken from just one output pin.
Regulated dual output converters regulate the difference between Vout+ and Vout- and allow the common pin to float. So if a +/-15V is asymmetrically loaded with, say +80%, -20%, then the output voltage difference will stay 30V, but the common pin will drift so that the output voltage will measure +13, -17V. If a balanced output is required with unbalanced load, then use post-regulation to stabilize the outputs.

When a control pin voltage is rising, the switching point (threshold) is higher than when the voltage is falling. The difference between the rising voltage trigger point and the falling voltage trigger point is the hysteresis. For example, a converter with negative control logic could switch on as soon as the control pin voltage exceeds 3V but once started, only switches off again when the voltage drops below 1V. The 2V difference is the hysteresis and stops the converter from switching on-and-off erratically with a slowly rising or falling control voltage.

Some RECOM converters, like the R-78AA series, have a two level control pin function. If the control pin voltage drops below 2.6V, the main power stage is switched off, but the internal oscillator and voltage regulator is kept running. This allows a very rapid restart from standby to full power. For ultra-low power mode, the control pin voltage must be below 1.6V. Then the main oscillator is also turned off and the converter draws only 20µA from the input. Start-up will be slower from deep sleep than from standby.

Negative control logic means that logic 0 (low) enables the converter and logic 1 (high) disables the converter. If the pin is left unconnected, it will be logic 0 and the converter will start up as soon as power is applied.
Positive control logic means that logic 0 (low) disables the converter and logic 1 (high) enables the converter. If the pin is left unconnected, it will be logic 0 and the converter will not start up when power is applied, but wait for a positive signal before starting. For many safety-critical systems, this is an important feature.

Quiescent or standby current is the current drawn by the converter from the supply when it is unloaded (the converter is active and has an output voltage, but no output current). The shutdown current is the residual current drawn by the converter from the supply while it is disabled by using the control pin. The control pin current is the current drawn by converter through the control pin in order to keep it in the disabled state.

The maximum allowed control pin voltage varies from converter series to converter series. Most DC/DC converters allow up to 5V and some up to 12V or more. Refer to the datasheets for guidance. Do not connect an unused control pin to +Vin unless this is expressly permitted in the datasheet.

All RECOM products will not be damaged if used without s load, although in some families some specifications may be out of range below 10% load.

Nickel plated copper or aircraft-grade aluminium, depending on the converter series.

We use a number of tin whisker mitigation strategies, all following the Jedec JP002 guidelines:

Through Hole Devices
The pins used in all of our through-hole converters are made of hard silver-copper alloy. The pins are then Nickel underplated to 0.5µm before being pure tin electroplated to 6µm thickness. This thickness of overplating is a compromise between reasonable manufacturing costs and having a thick enough coating to impair tin whisker formation. The surface is not ‘brightened’, also to mitigate tin whisker formation. Finally the pins are annealed according to JIS C3101. This reduces any residual forming stresses, which is one of the other potential causes of tin whisker formation.

Surface Mount Devices:
The carrier frames used in our SMD converters are made from DF42N nickel alloy which is pure tin plated. The pins are then hot dipped in Sn-Ag-Cu solder to mitigate tin whisker formation.

The converters are not vacuum potted because we use a special process to remove the air bubbles (voids). The epoxy potting process is as follows:
1- The two-component epoxy is mixed and placed under a vacuum for 1 minute to remove any air bubbles created by the mixing process.
2- The plastic case is 1/3 filled and allowed to rest.
3- The pre-tested converter pcb is inserted into the case and 2/3 filled and allowed to rest.
4- The part completed converters are placed in a warm oven (30°C) for 20 minutes to allow any air bubbles to rise to the top.
5- The case is sealed with a harder grade of epoxy and baked at 50°C for one hour to cure.
6- In addition, spot checks are made with our X-ray machine to monitor and ensure that air voids are not present in any of our converters.
The silicone rubber potting process is as follows:
1- The pre-mixed silicone rubber compound is injected into the case
2- The case is placed on to a shaker and vibrated to encourage any air bubbles to rise to the surface
3- The case is topped up to the fill level
4- The converters are put aside to cure at room temperature.

An unregulated converter is a cheaper solution but offers less output voltage stability. The output voltage can change depending on both the load and the input voltage variations. Therefore, the input voltage range is restricted to +/-5% or +/-10% , so it is recommended to use unregulated DC/DC cpnverters only with a regulated supply voltage. The output voltage can rise substantially during no-load conditions, but, even an unregulated converter offers a low output voltage variation over a 20% to 100% load range.

Regulated converters offer a much better load and line voltage regulation, typically less than 1%, so the output voltage is not dependant on the load or input voltage. In particular, the output voltage remains stable under low load or no load conditions. In addition, the input voltage range is higher (2:1, 4:1 or up to 7:1 with non-isolated converters), so regulated converters are suitable for use with variable input voltage supplies such a batteries or multiple supply voltages (e.g, 12V or 24V supplies)

The current drawn by the converter when it is idle (not loaded). All converters contain oscillators that absorb power even if no power is being drawn from the converter.

At a certain ambient temperature the internal heat dissipation makes it impossible for the converter to supply 100% of its power and the load must be derated (reduced) as the temperature goes higher. The derating curve shows the maximum power that the converter can deliver over the full operating temperature range. Some AC/DC converters allso have a low-temperature derating. This is due to increased losses caused by reduced efficiency at very low temperatures.

Different converters have different on/off control voltages. Please check the datasheets carefully before connecting the on/off pin to ground or +Vin as this can damage the converter. Some on/off pins may require additional external components if driven with a TTL level signal.

The higher power converters are optimized to run with the highest efficiency at full load. This means, for example, that the switching transistors need to switch very rapidly to avoid wasting power in the region between fully on and fully off. With no load, the switching drivers still run at full power which makes the converters run warm.

Low power converters that uses post-regulation must be designed so that at the minimum input voltage there is enough output voltage headroom that the linear regulator can regulate properly. This means that with the nominal input voltage, there will be a higher voltage drop across the linear regulator, which in turn will increase the quiescent current drawn by the converter.

Higher power converters often use synchronous rectification on the output. The switching transistors still run at full power even under no-load conditions, so this can lead to a high quiescent current.

Yes, if they are derated (not used at full power). However, the simpler low cost converters have no overtemperature protection. If they are used outside of the temperature specification for a long period of time, they may fail. Our higher power DC/DC and AC/DC converters are fitted with over temperature protection. If they overheat they will simply shut down.

The isolation voltage given in the datasheets is valid for 1 second flash test only. If an isolation barrier is required for longer or infinite time the Rated Working Voltage has to be used. Recom provides an isolation conversion calculator on the website to indicate the equivalence bewtween DC and AC isolation for 1s, 60s or continuous.
It is very important that you compare the same type of isolation when comparing our products with the competitors to avoid misunderstandings.

The MTBF (Mean Time Between Failures) is a calculated figure based on the chances of a random failure causing the converter to stop working - ignoring all of the real-life stress factors such as over voltage stress, under voltage stress, thermal stress, switching stress or component aging. It should not be confused with operational lifetime. For comparison, the MTBF of a 25-year old healthy person is around 800 years - meaning if that person never got ill, lived an ideal, unstressed lifestyle and never aged - so that the only cause of death would be accidental injury- then that person would theoretically live 8 centuries. MTBF is a comparative measure of reliabilty, but not an absolute measure.

The standard environment for MIL STD 217F calculations is Ground Benign.
The correction factors for other environments are:

Ground Benign (GB) = 1.00
Ground Mobile (GM) = 0.61
Naval Sheltered (GNS) = 0.61
Aircraft Inhabited Cargo (AIC) = 0.61
Space Flight (SF) = 1.00
Missile Launch (ML) = 0.32

MTBF (Mean Time Between Failures) of different components in a system can be added up to give overall board-level reliability. As MTBF is a standard measure used for all electronic components, it is useful to also have the figure for the DC/DC converter in the datasheets.
MTBF figures can also be used to compare the reliability of two different DC/DC products. The product with the highest MTBF will, in general, have the highest reliability. Care must be taken when comparing MTBF figures between different manufacturers as the way they are calculated may differ significantly.

All of our DC/DC converters contain a built-in input capacitor filter, so an external capacitor is not required for normal operation, unless specified in the datasheet. An input capacitor may also be required to meet surge requirements or to smooth the DC supply at the point of load. If several DC/DCs are powered from the same rail, then input capacitors placed close to the input pins are recommended.

Type is not critical. Actually, a lower quality, relatively high ESR capacitor on the input is actually an advantage as its internal resistance helps damp down any switch-on surge oscillations.
A combination of tantalum or electrolytic in parallel with an MLCC on the input or output combines the advantages of both types (high ESR to reduce ringing, low ESR to filter noise).