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FAQs

General

Product related

Powerline AC/DC

Econoline

Innoline

Powerline

Lightline

I can’t find any product that meets my requirements. Can you supply a customized converter for me?

In addition to the standard ranges shown in this data book, RECOM has the capability to produce custom DC/DC converters designed to your specific requirements. In general, the parts can be quickly designed to meet any input or output voltage requirements within the ranges of RECOM standards products (i.e. up to 48V at either input or output). Prototype samples can also be produced in short timescales. See our application notes for more information or contact Recom Technical Support.

Do RECOM products have certifications? What kind of certifications?

EN certificates are available for most of our converters. UL, and CSA listing for most of the higher power converters.

Are these parts EN-55022 Class B certified?

EMI filtering is not included inside the converters. However, an external EMI filter is suggested in our Application Notes for Class A and Class B. Most converters are Class B for radiated emissions or offer the option of a shielded metal case.

Is there any RECOM part medically approved?

We provide many converters medically approved, EN-60601 certified.

How can I clean these parts included in my board?

As with all electronic devices, strongly reactive agents in hostile environments can attack the encapsulating material and the pins, hence cleaning is recommended with inert solutions (e.g. alcohol or water based solvents) suitable for electronic components and at the temperatures recommended by the cleanser manufacturer.

I need to clean the board before conformal coating; we are concerned about the cleaning process for the RECOM parts.

You can use a non-aggressive, non-corrosive, water-based cleaning agent. The materials used in the converters are nickel plated copper for the metal case, cured two component epoxy (XT5038-6) for the potting compound and Diallyl Phthalate (DAP 901 - also known as Duroplast) for the plastic case. All of these materials are unaffected by any of the washing liquids suitable for cleaning PCB boards and also will not react with mineral oils, water-based compounds or even most solvents used in industry. 

The ambient temperature should not exceed 130°C for extended periods of time (several hours) as this is the maximum recommended use temperature of the epoxy.

Please refer to the instructions given by the conformal coating supplier regarding the recommended process for applying the coating.

We have many customers that wash their boards, both with aqueous and solvent-based washes, before applying a conformal coating or potting their completed pcb.

We have never received any complaints of chemical incompatibility or any other problems with washes or conformal coatings.

Can the converters be cleaned with an ultrasonic cleaner?

Yes. They can be ultrasonically cleaned as long as the cleaning fluid used is not aggressive and does not attack any of the metal, plastic or epoxy parts.

 

Note: We should take into consideration that some converters have empty holes (for optional features, such as control pins), so it’s possible that a small amount of cleaning fluid could wick its way through these holes and work its way under the base plate. This will not damage the converters (underneath the base plate it’s completely encased in epoxy) but be aware that if the board is baked to dry it off, the temperature of the oven should remain below 100°C so this trapped liquid doesn’t turn to steam and cause problems.

Why do I need a DC/DC converter?

There are many reasons why you should use a DC/DC converter, but the most common applications are: 

  • To match the loads to the power supply (e.g. to generate higher, lower or dual outputs from a single source, or to invert a supply rail.)
  • To isolate primary and secondary circuits (e.g. for safety reasons or to protect a sensitive circuit from interference)
  • To simplify power supplies (e.g. multiple output converters or one converter per rail (point-of-load) can reduce power supply complexity, overall cost and board space requirements while at the same time increasing flexibility, reliability and system efficiency. )

I can’t find information about the input quiescent current in your datasheets. Where can I get this information?

The input quiescent current can be determined using the no load power consumption spec, by dividing this value with the input voltage. If you need more information or the quiescent current for a particular operating condition, please contact Recom Technical Support

What’s the input quiescent current?

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. 

I am using a 12V battery as input source. Do I need any extra components?

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.

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.

What is Isolation?

Isolation refers to the electrical separation (galvanic isolation) between the input and the output of the converter. This means that the output of an isolated converter is not linked to the input and any electrical interference, voltage differences and fault currents are blocked. This is extremely important in applications where the output circuit is connected to the “real” world and the main circuit must be separated from anything that happens to the output circuit.

Why do you specify the Isolation for 1 second?

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 a conversion table in the Application Notes. 

Another useful measure is the isolation for 1 minute, which is also specified in the conversion tables provided in our Application Notes.

It is very important that you compare the same type of isolation when comparing our products with the competitors to avoid misunderstandings.

Do you have non-isolated converters?

All converters in the Econoline and the Powerline have isolation, only the Innoline offers non-isolated products.

What material is used in the metal case package?

Nickel plated copper.

Why does the On/Off function not work?

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.

I need more than 24V out in my application, but I can’t find anything in your catalog. How can I get this output voltage?

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 to the +ve input pin to boost a supply voltage. For example, a 12V battery feeding a 30W 12V output converter wired up this way will generate a 24V output voltage with 60W of available power (12V@30W from the battery + 12V@30W from the converter = 24V@60W)

Are RECOM parts RoHS compliant?

All RECOM products have been RoHS compliant since November 2005. You can find the chemical analysis reports for all our products in our website by clicking on the RoHS logo, which is located on our home page 

Do the AC/DC converters need any external components?

All AC/DC converters contain built-in mains filters, so no external components are necessary. However, some uses require an input fuse, which must be added externally. The –ST option (converters pre-mounted on an insulated PCB with screw terminal input and output connections) also contain an input fuse as standard.

Do RECOM products have reverse polarity protection?

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.

Are RECOM parts burn-in during production?

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

What measures have been taken to minimize tin whisker growth?

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 hot dipped in Sn-Ag-Cu solder just before injection molding.

What’s the difference between unregulated and regulated converters?

An unregulated converter is a cheaper solution but offers less stability over the output voltage. 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% and the output voltage can rise substantially during no-load conditions. However, even an unregulated converter offers a low +/-5% output voltage variation over the load range of 20% to 100%.

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 addition, the input voltage range is higher (2:1, 4:1 or up to 7:1 with non-isolated converters).

I am using one of your unregulated converter, but my output voltage is much higher than the tolerance specified in the Datasheets.

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.

Why some converters have higher Quiescent current than others? (e.g. RSZ or RY with built-in linear reg.)

A converter 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. 

Do you use triple insulated wire for the RP-xxxx and RxxP(2)xx series?

We use standard coated wire with both converters because the windings are physically separated (reinforced isolation). For the RP-xxxx series the primary and the secondary are separated by a chamber system. The RxxP(2)xx series uses a two chamber system which primary and secondary windings are separated by an insulated bridge on both sides of the toroidal transformer.

What process do you use to remove the air bubbles from the converter? Are the converters Vacuum potted?

The converters are not vacuum potted because we use a special process to remove the air bubbles.

The 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 with epoxy and allowed to rest.
  3. The pre-tested converter pcb is inserted into the case and 2/3 filled with epoxy 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.

Why should I replace my cheap Linear Regulators for a more expensive Switching Regulator (R-78 series)?

The R-78 costs more than a linear regulator because it is intelligent. It may look similar to a three-pin linear regulator, but inside is a controller chip that protects the converter against overload, over temperature and short circuits. This makes it very robust and hard-to-kill.

Even if the converter itself costs more, the savings that can be made in the primary power supply (because it needs less output current), assembly (because there is no fiddly heatsink, screw, nut and thermal paste to worry about) and inventory (one part rather than 7 parts with the linear regulator + heatsink + mounting + input and output capacitors) mean that the overall power supply cost can be lower with the R-78 than with the "cheap" linear regulator.

In the Innoline series, how does the continuous short circuit protection operate?

The Innoline series all use intelligent controllers that measure the output current on each switching cycle (Current Mode Control). If the output is overloaded, the converter will deliver the over-current until either the converter overheats and shuts itself down (thermal protection) or the load current exceeds the safe limits. If the output is short circuited, the controller shuts down the output drive circuitry. The output condition is continuously monitored and the converter automatically restarts.

Do I need any external components for the R-78 family?

No external components are needed. An input capacitor is recommended only if the input voltage exceeds 26V. An output capacitor helps reduce output ripple further, but the ripple is relatively low anyway.

Why do I need an input capacitor?

The input capacitor is required only if the input voltage can exceed 26VDC, otherwise it can be omitted.

Can I use a bigger capacitor in my output circuit?

Higher capacitance is allowed, but the capacitor may discharge back into the output of the converter if the input supply is suddenly removed. If the power supply input voltage decays gradually when powered down, then even 1000µF is ok. If the input voltage is suddenly disconnected, then the converter could be damaged by the reverse current flowing back into the output.

The suggested 220µF maximum output capacitance for the R-78 series is to help to protect the converter against reverse currents.

What type of capacitors do you recommend with the R-78 series? Are ceramics ok, or do you recommend tantalum?

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, so a ceramic input capacitor is overkill! Tantalum or electrolytic are therefore recommended for both input and output capacitors.

Recommended capacitor types are 3.3µF/50V Electrolytic on the input and 100µF/6V Electrolytic on the output.

Can I get a negative output out of the switching regulator?

Yes you can. Please refer to the Innoline Application Notes and find our recommended circuits to get a negative output from each series of our Switching Regulator families.

I am using my own discrete solution to drive my LED’s, why should I change it to your LED driver?

The RCD-24 series is a All-in-One solution in a small package with high efficiency, wide input range, two different ways of dimming Analog and Digital (PWM), high operating temperature range, and it’s fully tested. You don’t have to worry about all different suppliers of all the components of your discrete solution.

The PWM-control pin can be used as remote control pin as well. It means you can switch the unit on/off via this pin. Switching level is TTL compatible and has hysteresis to allow slow switching waveforms.

 

What’s the linearity range of the dimming function?

The linearity outside the 10~90% range of the PWM dimming is not perfect, but still pretty good. The Analog dimming can be used in a 0~100% range.

How does the Analog dimming function work?

The analog voltage is used to control an internal PWM circuit.

How does the PWM dimming function work?

The controller chip has a multi-stage shutdown:

      On :  Open or 0V < Vr < 0.6V

minimum quiescent current - all circuits shut down - slowest restart response time

      Off (Standby) : 0.6V < Vr < 2.9V

output power stage and PWM oscillator off - medium restart response time

      Off (Shutdown) : 2.9V < Vr < 6V

output power stage off, all other circuits active - quickest restart response time

 

I am driving ten LED’s of 1Watt with your RCD-24-0.35 part using a 12V battery as input, but it’s not working properly. Why?

The RCD-24 series is step-down (buck) converter. You always need a higher input voltage than the output voltage required. A high power LED usually has a forward voltage drop of around 3.4V, so only three LEDs can be driven from a 12V source. If the input voltage is increased to 24V, seven LEDs can be in the chain and if the input voltage is 36V, then ten LEDs can be driven.  However, it is possible to connect chains of LEDs in parallel, so a RCD-24-7.0 can drive two chains of three 350mA LEDs connected in parallel.

Remember that this part is a constant current converter, so the output voltage is variable depending on the power needed, but it will always be lower than the input voltage.

Is required any input or output capacitor?

For normal function, no external capacitor is needed. For EMI filtering, consult our recommendations in our Application Notes.

Can I use the Common Mode Choke used in my EMI filter to limit the Inrush current as well?

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 works ok.

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.

 

I have temperature problems. Can I use a heat sink to increase the temperature range?

The converters have a derating curve that starts usually between 70°C and 85°C. From that temperature point the power is reduced linearly. You can use a heat sink to move this temperature point up a few degrees. If your application doesn’t have a adequate ventilation system, even a large heat sink may not be effective. The solution would be to use a higher power converter instead.

Why do you specify a Derating Curve?

At a certain temperature the internal heat dissipation makes it impossible for the converter to supply 100% of its power and it starts to gradually provide less power as the temperature goes higher. This temperature is specified as Ambient Temperature.

Why does the RP40 series run hot with no load?

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.

Can the converter be externally synchronized?

Recom does not offer this feature in any of its 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.

How do I interface a dual supply (AC and DC inputs)?

A simple solution is to automatically switch inputs using a mains-powered relay. The AC/DC converter does not mind having a DC voltage on its output when it is not powered up (this is a useful feature that enables, for example, a board to be powered up and tested on a bench using a safe DC supply and then only plugged into the mains when the unit has been reassembled into its case).

Do all your converters include input surge protection?

No, not all of our converters include input surge protection, for those who do not state that input surge protection is included on their datasheets we suggest you use a suppression diode and/or an input capacitor as input surge protection.  

Will your converters operate the above operating temperature range?

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 converters are fitted with over temperature protection. If they overheat they will simply shut down. 

What is the minimum load for the converters?

RECOM converters dont have a minimum load required for operation, although in some families some specifications may be out of range below 10% load.

Does the isolation apply to both high and low side between the input and output?

The isolation is tested with the inputs shorted together and the outputs shorted together and then the test voltage is applied between the input and output side. In this way the insulation is tested for all possible pathways between input and output, so the value applies equally for the low side and high side input. 

Why the RAC04 series doesn't have the -E (extended lower temperature range) option?

The RAC04 family already works at -40degC (extended temperature), so it doesn't need the additional suffix (-E).

Is there a minimum load requirement for the R-78 series?

It is recommended that the R-78 series of switching converters is used with a minimum load of 6mA to guarantee that the output is stable under all operating conditions.

How does the enable pin on the ROF-78 work?

The enable pin on the ROF-78 has a max voltage of ~15V, (5-36)V.

1.25V is the threshold voltage, below that voltage the converter should be OFF. Above 1.25 the converter will be ON. The 0.9V and 1.55V values are recommended safety values to ensure that below 0.9 it will be OFF, and 1.55V it will be ON.

In short, if you want to ensure that the device is on continuously, apply &gt;1.55V to the EN pin all the time

How does the enable pin on the R-78AA series work?

The enable pin has two functions: Below 2.6V, the converter is OFF (the output power stage is switched off, but the converter oscillator is still running). Below 1.6V, the converter is in ultra-low power mode ( 20µA shutdown mode).

Can I tie the on/off pin of the R-78AA family to the Vin pin if Vin goes up to 32V?

The absolute maximum voltage accepted in that pin is 15V, although its not recommended to go higher than 5V. You cant connect the input directly to the control pin

Do you offer dimmable AC supply LED drivers?

Yes, for our AC input drivers we offer 0-10V analog dimming, TRIAC dimming, and Thermal dimming.  This can be found in our RACD20-D, RACT20, and RACD60/TOF respectively.

The datasheet of the RACD60 says has dual capabilities and can be used with a constant voltage or constant current output, does that mean I can choose how I want the driver to function?

As long as the output current is below the preset value the LED driver operates in CV (constant voltage mode).  When the output current is lower than the preset current the drivers switches to CC (constant current) mode.

Do you have constant voltage LED drivers?

Yes, our RACD03, RACD06, RACV30, and RACD60 can be used as constant voltage drivers.

What function has the case pin?

The case pin is an electrical connection to the metal case or baseplate. It can be used to improve the EMC performance in certain applications by tying the case to ground or to Vin+. If not used, it should be left open.

What function have the sense pins?

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 measure 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.

Can the output voltage of a switching regulator be increased by adding a resistor to the GND connection?

No. Switching regulators function differently than linear regulators and this “trick” does not work. They need a very good ground connection to function properly.

Can the output voltage be trimmed by an external voltage or current rather than by a resistor?

In theory, yes, but in practice it is very non-linear. It is not really recommended.

What function has the trim pin?

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%).

What is the maximum control pin voltage?

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.

What is multi-level control pin function?

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.

What is the difference between quiescent or standby current, shutdown current and control pin current?

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.

What is control pin voltage hysteresis?

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.

What is positive or negative control pin logic?

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.

What function has the CTRL pin?

The Remote On/Off or Control pin is commonly used for the following reasons:

  1. 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.
  2. 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.
  3. 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.
  4. 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.

What happens if I use an unbalanced load on a dual output converter?

Some unregulated 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.

What are the output options of DC/DC converters?

The main output options are:

  • Single output, with Vout+ and Vout- pins. This is the most commonly used option.
  • Dual (bipolar) output, with Vout+, Com and Vout- pins, e.g. +/-15V. Useful for generating bipolar supply rails from a single input voltage rail, e.g, to supply an op-amp.
  • Dual (asymmetric) output , with Vout+, Com and Vout- pins, e.g. +18, -9V. Useful for IGBT driver applications which uses asymmetric supply voltages.
  • Dual (independent) output, with Vout1+, Vout1- and Vout2+, Vout2-, where the outputs are isolated both from the input and from each other. Useful for supplying a two-channel application using only one converter.
  • Triple output, with a main Vout+ and  Aux+, Com and Aux- pins, e.g. +5V and +/-12V. Useful for applications requiring a single high current supply and an auxiliary supply to power peripherals.

Does it matter of the input is positive or negative voltage compared to the output voltage?

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).

What happens if I connect the Vin+ and Vin- the wrong way around?

DC/DC converters are not reverse polarity protected. They will be irreparably damaged if connected the wrong way around. If it is possible or likely that the converter could be reverse polarity connected, then a diode must be used to protect the converter (refer to the application notes).

What is the difference between a 1:1, 2:1 and 4:1 DC/DC converter?

The ratio refers to the input voltage range. A 24V input DC/DC converter with 1:1 input range is specified with 24V input +/-10% (21.6V to 26.4V). A 24V input DC/DC converter with 2:1 input range is specified over a two-to-one input voltage range of 18V-36V and a 24V input DC/DC converter with 4:1 input range is specified over a four-to-one input voltage range of 9V-36V.

What pin functions does an isolated DC/DC converter have?

A DC/DC converter can have the following connections

  • The supply pins,
  • Vin+ and Vin –
  • The output pins,
  • Vout + and Vout- (plus a common pin for +/- outputs)
  • A remote on/off,
  • enable or control pin
  • A trim pin
  • Sense Pins
  • Case pin

What is the function of an isolated DC/DC converter?

An isolated DC/DC converter will translate a DC input voltage to the same or a different DC output voltage which is electrically isolated from the input via an internal transformer. It is commonly used for the following reasons:

To match the load to the input. For example to convert an input voltage which is higher or lower that what is required by the load. A common requirement is to convert a 24VDC supply to an isolated 5V output or to generate +/-15V supply rails from a 5V source.

To stabilise a power supply. Battery-powered equipment has to work with a variable input but many circuits require a stable supply voltage. For example, a typical 12V-to-12V DC/DC converter can deliver a stable 12V output from an input voltage range from 9V up to 18V.

To isolate a supply. An isolated DC/DC converter can be used for safety (for example in medical applications) to protect the user from power supply faults, or it can be used to break earth-loop connections to reduce noise and interference  (for example, a DC/DC used in a motor controller circuit can provide a low-noise, stable output from a noisy DC supply). For applications with multiple channels, isolating each channel power supply with a separate DC/DC converter means that if any channel is faulty or short-circuited, the remaining channels are unaffected.

To simplify a power supply. An application requiring many different board-level voltages can be made simpler and more reliable by using a single main supply voltage followed by DC/DC converters at the point-of-load to generate local power.

What is the function of a non- isolated DC/DC converter?

A non-isolated or switching regulator converter can efficiently reduce or boost a DC input voltage to a lower or higher output voltage. A switching regulator has the following advantages over a simple linear regulator:

As a transformer is not used and the input and output share a common ground, the efficiencies can be very high (>97%) compared with a linear regulator (typically 20% when dropping 24V down to 5V, for example).

A switching regulator varies the internal on/off duty cycle to compensate for changes in load and/or input voltage. Thus the converter can work efficiently over a wide input voltage range (7:1) and wide load range (100:1).

A switching regulator is a power converter, so for a fixed load, the input current reduces as the input voltage increases. This allows for high output currents without overloading the input.