There may come a time in your career as a PCB designer when your designs will fall under the purview of some kind of regulatory requirements. Whether it be medical, automotive, military, or anything of the sort, your design could end up being scrutinized and held to very high standards. Oftentimes, when these regulations are in effect, power isolation (or lack thereof) suddenly becomes a very popular topic.
What is power isolation, and what is an isolated power supply? Power isolation is essentially what it sounds like: the power supply is isolated from the rest of the circuits in your system. This is a common measure in power systems, and for good reason. For example, with a non-isolated power supply powering your medical PCB, there is a greater risk for dangerous shocks or surges surge through the supply and into your device, potentially harming the user (and maybe even the patient!).
An understanding of isolated vs. non-isolated power supplies is all about designer and user safety. Here, we're not talking about only the AC or DC power supply units you find the lab. For many digital and embedded systems, the power supply is integrated into the board, and it doesn't appear as a single integrated circuit. Power supply isolation, even when integrated into the board or into a multi-board system, will help protect the end user and other equipment. So let’s all do ourselves a favor, and consider the difference between an isolated vs. non-isolated power supply before starting your design.
An isolated power supply is a power supply that is electrically isolated from the rest of the circuit that it is powering, often by an isolation transformer. This means that power and voltage is transferred from the input to the output without a direct electrical connection between the two sections. These power supplies can accept a large input voltage from AC mains and convert the input down to a lower voltage. Subsequent PFC and regulator stages might be used to limit the output current to a stable value, which ensures the downstream components are protected from large voltage and current surges at the power supply input.
For a lab-grade DC or AC power supply, the user will need to interact with the output stage of the isolated power supply. In other words, they may need to plug or unplug wires, adjust some settings on the front panel, or otherwise handle the power supply unit. By isolating the input from the output, the end user of the power supply is at lower risk of shock when they work with the power supply. A typical topology for converting AC to DC with an isolated power supply is shown below.
Simple topology for the output stage of an isolated power supply via an isolation transformer.
In the above topology, a step-down transformer is shown at the input (between any input EMI filtering and the rectifier circuit) as part of AC-DC conversion, but often times this will be placed after the rectifier and PFC stages, particularly in an isolated DC-DC switching converter. Typically, in high current switching DC-DC converters that require isolation, the strategy in isolated DC-DC power supply design requires driving a half-bridge or full-bridge array of MOSFETs with a pulse stream supplied by a gate driver circuit. This is basically what is done in a resonant LLC converter. The pulsating output from this circuit is then stepped down to a lower voltage with a transformer and smoothed with a capacitor bank. This is also done in a flyback converter, which is a common type of isolated DC-DC switching converter, although the topology may be different.
The above topology doesn't explicitly show you something important: how isolation is actually implemented and the overall grounding strategy. In an isolated power supply, there may be up to 3 ground regions:
Note that the designations "PGND" and "SGND" are not required; you can technically name your nets anything you want. How these regions are actually connected to eliminate noise and ensure safety while maintaining DC isolation depends on the application. Here are some resources to help you get started in these systems:
The images below show a design example involving an isolated power supply. In this supply, we actually have two levels of isolation applied between the input and output:
The AC input stage is not shown below as there are multiple reference designs that can handle the initial AC/DC conversion task. The output from the AC rectification stage is fed into a PFC circuit that compensates for reduction in the converter's power conversion efficiency through switching action. The isolated switching stage is shown below.
This is an LLC resonant switching converter, and it is a variant of a design I've shown elsewhere. There is an additional gate driver circuit that switches the stages on the primary and secondary sides of this resonant converter. We know that this converter is isolated because the primary and secondary grounds are different nets; they are only connected with a safety capacitor.
Other standard isolated power supply topologies are shown below. These are only topologies; a gate driver is also needed to drive switching action. A feedback mechanism is also used in real isolated power supplies; the feedback circuit measures the output and adjusts the driving PWM signal is used to maintain a target voltage.
One point to note about the above topologies is that the circuitry could be partially or totally integrated into an integrated circuit. These integrated circuits provide high galvanic isolation, but with integrated feedback and supporting circuitry needed for low noise. They are more common for use in low-power systems that require low noise and high efficiency.
An isolated power supply uses an isolation transformer to provide galvanic isolation between the input and output sections. Transformers simply transfer power between coils using the magnetic field generated by an alternating current in each coil, and the voltage is stepped either up or down, depending on your turns ratio in the transformer. The benefit of isolation with a transformer is that there is no direct electrical connection between the input and output coils on the transformer; the conductors on each side do not touch each other. Power is transferred across the two ground regions in the device via induction. This keeps anything downstream of the transformer protected from high voltage/current on the input side, or, in other words, everything downstream is ‘isolated.’
When a feedback loop is needed for monitoring and control over the output power, an opto-isolator is normally used to link the output back to an earlier regulator stage. This component uses an infrared diode to ensure isolation between high power and low power regulator stages. For power supplies that run at low voltage / current, an opto-isolator can usually be connected directly to the output, although there are some opto-isolator ICs that can receive larger voltage / current levels.
One point to consider in an isolated power supply is its efficiency. All transformers have some losses, both in the form of heat dissipated in the winding and due to alternating magnetization in the core. The magnetic material used in the core (usually iron or a ferromagnetic alloy of iron) becomes magnetized back-and-forth as the input AC current oscillates. When the magnetic field created by the AC input is very large, it can cause magnetization in the core to saturate, which limits the output power (decreases efficiency) and creates greater core losses. This is one of the factors that determine primary voltage ratings on the two sides of the transformer.
This type of transformer might be found in a large isolated power supply.
Now that we know what isolates a supply from your board, it becomes rather obvious that taking the transformer out of the design chain suddenly makes it a non-isolated power supply. Designing a board without power isolation is common, however if you are working at high power or you are using a fast switching supply, consider the end-user along your design journey, as you might just save yourself a court case or two when your favorite customer receives a shock they won’t soon forget.
The upsides of designing these non-isolated power designs are plentiful. First, you’ll enjoy more board space relative to an isolated power supply design due to the fact that you won’t need to put a transformer in your enclosure. There are small off-the-shelf transformers for lower voltages/currents, but as you scale up you gain more board space. You'll may also benefit from increased efficiency with a non-isolated power supply.
Non-Isolated supplies always hold the risk of electrical shock through the design.
It is worth noting that it is common practice to place non-isolated power regulator downstream of an isolated power supply or isolated switching regulator. In this strategy, the isolated power supply is placed at the high power AC or DC source, which then drops the voltage down to a level that is safe enough for a standard DC regulator IC or voltage regulator circuit. This is a bit more complex, but it has the advantage of giving you the proper protection that checks off your safety requirements. An example of this may look like a standalone medical power supply (isolated) that feeds a handful of devices (non-isolated) downstream.
In summary, typically the power regulation circuit on your board will simply be a non-isolated power supply. These are built from small regulator circuits or chips that do not require isolation because they may not be generating much current or operating at very high voltage. Even if they do operate with high current, the user may not ever interact with the system in such a way as to be at risk of shock. Therefore, non-isolated supplies are just fine for the majority of smaller boards. This will usually just be a buck converter followed by an LDO to regulate power down to the required level.
When you need high power AC to DC conversion, or high power DC to DC conversion, you'll generally use an isolated supply, and many times the power supply will be designed on its own board. What happens next depends on the particular characteristics of your power source (AC vs. DC, mains vs. battery, etc.), how your enclosure will be used, and how ground is defined in any downstream circuits or systems connected to your power supply.
As previously stated, isolated power supplies are often required for regulated industries and must perform to certain standards. Examples include:
Some regulations do not specify certain industry standards (for example, US FDA regulations on cardiovascular devices in 21CFR870.), but they do mandate safety and EMC testing to ensure these devices will be fully compatible with other electronics and basic safety standards in their intended environment.
As energy laws have gotten stricter, most people know that LEDs, or light-emitting diodes, last a long time and save energy. But few people understand that these high-tech light sources can’t work without an LED driver. LED drivers, sometimes called LED power supplies, are like ballasts for fluorescent lights or transformers for low-voltage bulbs. They give LEDs the electricity they need to run and work at their best.
An LED driver controls how much power an LED or a group of LEDs needs. Since light-emitting diodes are low-energy lighting devices with long life and low energy use, they need specialized power sources.
The main jobs of LED drivers are to provide low voltage and protect LEDs.
Each LED can use up to 30mA of current and work at voltages of about 1.5V to 3.5V. Multiple LEDs can be used in series and parallel to make home lighting, which may need a total voltage of 12 to 24 V DC. The LED driver turns the AC around to meet the needs and lowers the voltage. This means that the high AC mains voltage, which ranges from 120V to 230V, must be changed into the low DC voltage that is needed.
The LED drivers also protect the LEDs from changes in voltage and current. Even if the mains supply changes, the circuits ensure that the voltage and current going to the LEDs stay in the suitable range for them to work. The protection stops the LEDs from getting too much voltage and current, which would hurt them, or insufficient current, making them less bright.
When the temperature of an LED changes, so do its forward voltage needs. As it gets hotter, less voltage is needed to move current through the LED, so it uses more power. Thermal runaway is when the temperature goes up out of control and burns out an LED. The power output levels on LED drivers are made to meet the needs of LEDs. The driver’s constant current keeps the temperature stable by responding to changes in the forward voltage.
Transformers for low-voltage light bulbs do the same thing that LED drivers do for LEDs. LED lights are low-voltage devices that usually run on 4V, 12V, or 24V. To work, they need a source of direct current power. But because wall socket power supplies typically have a much higher Voltage (between 120V and 277V) and produce alternating current, they are not directly compatible. Since the average voltage of an LED is too low for a regular transformer, special LED drivers are used to convert high-voltage alternating current to low-voltage direct current.
The other thing that LED drivers do is protect against power surges, and changes, which can make temperatures rise and light output go down. LEDs are made to only work within a specific range of amps.
Some LED drivers can also change the brightness of the connected LED systems and the order in which the colors are shown. To do this, you must carefully turn each LED on and off. For example, white lights are usually made by turning on a bunch of different-colored LEDs at the same time. If you turn off some of the LEDs, the white color disappears.
Differences between external and internal LED drivers can be built into lamps (interior), put on the surfaces of light fixtures, or even put outside of them (External). Most low-power indoor lights, especially bulbs, have LED drivers built in. This makes the lights cheaper and more attractive. On the other hand, downlights and panel lights usually have LED drivers on the outside.
When using a lot of power, like street lights, floodlights, stadium lights, and grow lights, external LED drivers are used more and more. This is because the heat inside the lights gets worse as the power goes up. Another good thing about external LED drivers is they can be easily changed for maintenance.
Because linear LED drivers are so simple, a resistor, a controlled MOSFET, or an IC may be all needed to make an LED’s constant current. A lot of AC LED, sign, and strip applications use them. Because of this, power supplies can change very easily, and there are now a considerable number of constant voltage power sources, such as 12V and 24V LED drivers. A linear regulator wastes a lot of power, so the light can’t be as bright as it could be with a switching power supply.
High-efficiency switching supplies naturally lead to high light efficacy, which is the most important thing for most light applications. Also, switching power supplies flicker less, have a higher power factor, and can handle surges better than AC LEDs.
When we compare these two things, we call each of them a switching power supply. According to UL and CE regulations, the isolated design usually works at 4Vin+V and Vac, and the input and output voltages are well separated. Using a highly insulated transformer instead of an inductor as the part that transfers human power makes the system safer. Still, it also makes it less efficient (by 5%) and more expensive (by 50%). Insulation keeps the high voltage from going from the input to the output. On the other hand, low-power built-in designs usually use non-isolated designs.
Because LEDs have unique V-I characteristics, it goes without saying that a constant current source should power them. However, a constant voltage LED driver can be used if a linear regulator or resistor is connected in series with the LED to limit the current. Signs and strip lighting usually use constant voltage LED drivers with 12V, 24V, or even 48V because they are much more efficient than constant current LED drivers, which are the norm for general lighting like bulbs, linear lights, downlights, street lights, etc. As long as the total wattage doesn’t exceed the power supply’s limit, the constant voltage solution makes it easy for users to change the amount of light, giving it much flexibility for installation in the field.
In this case, I and II are written in Roman numerals instead of 1 and 2, which means something completely different, as you can see in the next item. IEC (International Electro-technical Commission) regulations use the terms Class I and Class II to describe how a power supply is built on the inside and how it is electrically insulated to keep users from getting an electric shock. IEC To keep people from getting shocked by electricity, Class I LED drivers must have protected earth connections and essential insulation. There is no need for a protected earth (ground) connection because IEC Class II input models have extra safety features like double or strengthened insulation. Class I LED drivers often have a ground connection at the input, while class II drivers don’t. However, class II drivers have higher insulation levels from the input to the enclosure or the output. And here are the most common symbols for classes I and II.
The Arabic numbers 1 and 2 stand for the NEC (National Electric Code) ideas of class 1 and 2, respectively. These ideas describe the output of a power supply with less than 60Vdc in a dry location and 30Vdc in a wet spot, less than 5A current, and less than 100W power, as well as the detailed requirements for the circuit design feature. Using class 2 LED drivers has a lot of benefits. Their output is considered to be a safe terminal, so no extra protection is needed at the LED modules or light fixtures. This saves money on insulation and safety tests. UL and UL set the rules for Class 2 LED drivers. But because of these limits, a Class 2 LED driver can only power a certain number of LEDs.
In this new time, every light is made to be dim. This is a big subject because there are many ways to dim lights. Let’s talk about each one in turn.
1) 0-10V/1-10V dimming LED Driver
2) PWM dimming LED Driver
3) Triac dimming LED Driver
4) DALI dimming LED Driver
Link to Eaglerise
5) DMX dimming LED Driver
6) Other Protocols of LED Driver
IEC uses the IP (ingress protection) certification as the only way to classify the degree to which LED drivers are waterproof. The IP code is made up of two numbers. The first number rates the protection against solid objects on a scale from 0 (no protection) to 6 (no entry of dust), and the second number rates the protection against liquids on a scale from 0 (no protection) to 7. (8 and 9) don’t come up very often in the lighting business. LED drivers with IP20 ratings or lower are used inside, while waterproof drivers are used outside. But this doesn’t always happen. For example, some indoor applications use waterproof LED drivers because they can put out much more power than low IP ones without needing an active cooling system, making them last less than IP-rated LED drivers.
When light bulbs were made for the first time, they had a mechanism inside them. The job of this thing was to slow down the flow of electricity through a circuit. Ballast is the name of this thing. If this wasn’t used in light bulbs and T8 light bulbs, there was still a chance that too much electricity could build up (tube lights). Ballast is still used in bulbs and tube lights to keep the current from getting too high. Ballasts are also often used with HID, metal halide, and mercury vapor lights.
Inductors, also called magnetic ballasts, give some lamps the right electrical conditions to start and run. Act as a transformer, giving out clean and accurate electricity. Even though it was made in the s, it was used from the s to the s. You can find them in High-Intensity Discharge (HID) lamps, Metal Halide lamps, mercury vapor lamps, fluorescent lamps, neon lamps, and so on. Before LEDs started to replace this technology around , it was used in almost all important parking lots and street lights for about 30 years.
In an electric ballast, a circuit is used to limit the load or amount of current. Electronic ballast tries to keep the flow of electricity more steady and accurate than magnetic ones. People started using these more in the s, and they are still used today.
A ballast controls how much electricity goes to the bulbs and gives them enough power to turn on. Since lamps don’t have control, they can use too much or too little electricity on their own. The ballast ensures that the amount of electricity going into the lamp doesn’t exceed what the light’s specifications allow. Without a ballast, a light or bulb will quickly draw more and more electricity, which could get out of hand.
When a ballast is put into a lamp, the power is stable, and the ballast controls the energy so that the current doesn’t go up even when the lights are connected to high-power sources.
LEDs don’t need a ballast for several reasons. First of all, LED lights don’t use much electricity. Also, you need an AC-to-DC converter since LEDs usually run on Direct Current (DC). The socket must be wired directly when switching to LED corn light bulbs. Lastly, because LEDs are much smaller than bulbs and tube lights, there is no extra space for ballast to fit. LED drivers can be made to take up much less space. Some experts also think that because LEDs don’t need a ballast, they use less energy and give off more light.
LED and fluorescent lights can’t work without a converter between the bulb and the power source. On one hand, standard incandescent lamps heat a filament with electricity to make light. LEDs, on the other hand, use led drivers instead of ballasts. Ballasts and lead drivers do many of the same things, so getting them mixed up is easy.
This is made possible by fluorescent ballasts, which send out a high-voltage spike at the start of the lamp’s life. Once the light is turned on, this spike acts as a current regulator. The led power driver changes the power source into a specific voltage and current, which then makes the LED light up. Both of them keep the light from being affected by the power source.
An LED driver is needed to change the alternating current into the direct current that LEDs need. LEDs can’t be powered directly by alternating current, so an LED driver is required to change it. Ballasts have changed a lot in how they are made and how complicated they are. Ballasts can run fluorescent lights but not LEDs or lights that use less energy. Several LED drivers seemed to have taken out the ballasts. Because it works better, the LED driver can do most of the things that the ballast does.
Instructions for setting up LED drivers
Would you like LEDs to be less bright? Or do you plan to change how bright it is? Then choose a dimmable driver or power supply. Why? The power sources are easy to tell apart because of how they work. The specifications table also has extra information, like what kinds of dimmer controls can be used with the drivers.
One of the first things to consider is how much voltage your lamp needs. So, if your LED needs 20 volts to work, you should buy a 20-volt driver.
In short, the goal is to ensure that your driver gets the right amount of power. The general rule is that you should do your job within the range of the light.
For a constant-voltage driver, you can also think about the voltage range. But you can measure both voltage and current ranges with a constant-current driver.
Pay attention to how much voltage the proposed LED light will use. So, ensure the LED driver can handle the voltage from the LED. In this way, it is easy to step down to the needed output voltage.
Also, you should think about watts. During this process, make sure to buy a driver with a higher maximum wattage than the light.
The power factor helps determine how much power the driver uses from the electrical network. And the range is usually from -1 to 1. Since this is the case, a power factor of 0.9 or more is the norm. In other words, as the number gets closer to one, the driver works better.
Your LED drivers should meet several different standards. For example, we have UL classes 1 and 2. Use the UL Class 1 for drivers that put out a lot of voltage. The fixture needs to be set up safely for drivers in this group. It can also hold more LEDs, which makes it work more efficiently.
At the level of LEDs, the UL Class 2 drivers don’t need a lot of safety features. It also meets the standards set by UL. Even though this class is safer, it can only run a certain number of LEDs at a time.
The IP rating is another way to measure how safe a driver’s cage is and what it can do. If you see IP67, for example, it means that the driver is safe from dust and brief immersion in water.
This part is crucial because it shows how much power the LED driver needs. The value is shown in terms of percentages. So, you could expect it to work between 80% and 85% of the time.
Low voltages of 12 to 24 volts power LEDs with direct current. So, even if your AC voltage is high, between 120 and 277 volts, an LED driver will change the direction of the current. In other words, stepping down from alternating to direct current is helpful. You can even find the right amount of high and low voltage.
LED drivers keep LEDs safe from changes in voltage or current. If the voltage of an LED changes, the current supply may change. Because of this, LED lights’ output is inversely related to how many they have. LEDs are also only supposed to work within a specific range. So, too little or too much current will change how much light comes out or cause the LED to break quickly because it gets too hot.
Overall, LED drivers have two main benefits:
Other light sources can be turned off quickly by changing the voltage, but LEDs can only be turned off by changing the ratio of voltage to current. Because of this, there are different ways to dim LEDs:
Most of the time, every LED light source needs a driver. But the main question should be, “Do I have to buy one separately?” The problem is that some LED light bulbs have a driver built right in. Also, LEDs made for home use often come with LED drivers. And a great example is 120-volt bulbs with bases that are either GU24/GU10 or E26/E27.
Low-voltage LEDs, such as tape lights, MR bulbs, outdoor-rated lights, panels, and other lighting fixtures, need an LED driver to work correctly.
When working with low-voltage LEDs, you need LED drivers. But you can’t say the same about 120-volt LED bulbs used in homes.
LEDs can be put in HighBay mounting and print mounting in several ways, depending on the project’s needs: For example, so-called SMD (surface-mounted device) LEDs can be used in tighter spaces. Because they can be soldered onto printed circuit boards, they don’t need wires. Still, check to make sure that all of the parts fit together.
In bigger rooms, there needs to be more light. Because of this, factory halls and department stores use HighBay spotlights, which are powerful ceiling lights. These have to be wired separately, but they are very strong. They can be wired to the standard mains voltage of 230V AC. To keep the LEDs from getting too hot, drivers like the XBG-160-A are connected in front of them. These have protection against overload that can actively limit how much current is sent.
This LED driver only needs a fixed amount of output current and a range of output voltages. Constant current is a specific output current measured in milliamps or amps and has a range of voltages that change depending on how much the LED is being used (its wattage or load).
Constant-voltage LED drivers have a constant output voltage and a maximum output current. The LED module also has a regulated current system that a simple resistor or an internal constant-current driver can power.
They only need a single steady voltage, usually 12 or 24 volts DC.
Theoretically, this LED driver could run halogen or incandescent lights with low voltage. But standard transformers can’t be used with AC LED drivers because they can’t tell when the voltage is low. So, they have transformers that don’t have a minimum load.
With these LED drivers, you can dim your LED lights. It also lets you control the brightness of LEDs with a constant voltage. And it does this by reducing the amount of current that goes to the LED light before it turns on.
With high-quality automotive LED drivers, you can tell the difference between your car’s inside and outside lighting systems in many ways:
LCD backlight LED drivers often use a specific dimming scheme to control the backlight’s brightness.
You can set up your devices with LED drivers to have infrared lighting. It can also be done with the help of a multi-topology constant-current controller.
With RGB LED drivers, you can add an animation or an indicator to your LED arrays with more than one color. Also, they often work with many standard interfaces.
With the help of LED display drivers, you can control which LED strings use the least and most power. So, these drivers can be used with either a large narrow pixel or a matrix solution for small or mini LED digital signage applications.
To figure out what size LED driver will meet your needs, you need to know the following:
If there are any other technical factors, like the need for precise color control or the possibility of water exposure, that can affect how the LED drivers work. The LED’s IP rating shows how resistant it is to water; a higher rating means it is more resistant. With an IP rating of 44, the product can be used in kitchens and other places where water might occasionally splash on it. A driver with a high IP rating, like 67, can be used outside. Drivers with an IP rating of 20 should only be used inside, where it’s dry.
More information, you can read How To Choose the Right LED Power Supply.
LED drivers are used in many different industries, just like LEDs. You can also light your space with the wide range of transformers, power supplies, and drivers available. Because LEDs are so flexible, adding smart features and changing the brightness is easy. In this way, LED drivers are essential to making modern, practical, and cost-effective lighting.
The company is the world’s best non-isolated led drivers supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.