How to choose a PCB power supply?
DC-DC converters are found in almost all modern electronics. The applications of DC-DC converters range from consumer electronics to industrial and military systems.
DC-DC converters are electronic circuits that convert one direct-current voltage or current level to another.
In most cases, devices only use one power source. However, if different sub-circuits require different voltages to work properly, you need to convert the input voltage to a lower or higher dc-level. That can be done with DC-DC converters. They also help to regulate and stabilize the output current and output voltage, keeping the voltage constant and preventing short circuits from damaging the power supply and other equipment.
Linear & Switching DC-DC Converters
Linear converters reduce output voltage with a resistor/resistive load. In a typical circuit of this type, the input and output are connected with a transistor. The input voltage is reduced by the voltage across the transistor which causes the output voltage to drop. These linear converters can only be used to decrease voltage, a so called stepdown converter.
Such circuits are quite simple and cheap but have a few disadvantages. Their efficiency drops as the difference between the input and output voltage rises. If the device isn’t powered by batteries, this drop can be less relevant but this unused power dissipates as heat which can affect the stability and life-time of your product. Linear converters are simple in your design, use a few components, and can save a lot of space.
Switching converters use a switching element that charges a storage capacitor with electrical pulses. This voltage is then smoothed with the capacitor and transferred to the load. The output voltage level is defined by the duty cycle of the switching element.
The efficiency of switching converters is much higher, they easily reach around 90%. That is why engineers prefer using them in battery-powered devices. Since they’re more efficient, they do not generate as much heat and can be used to step down or boost the output voltage.
Step-up DC-DC converters
Also called DC-DC boost converters, they can produce an output voltage higher than the input voltage. Typically the boost converter works as follows: the induction coil receives almost all the current, while the closed diode doesn’t let the current charge the capacitor and the load. Due to a higher electric current, the coil accumulates much more magnetic field energy compared to a step-down schematic.
Buck-boost converter
Buck-boost converters can increase and reduce the input voltage to produce a higher or lower output level. This type of converters is often used when you deal with a wide input voltage range. For example, it’s typical for car batteries. When the battery is fully charged it gives a voltage if often above 12Volt, when it is almost empty the battery gives a much lower voltage. A sepic converter: a single ended primary inductor converter is used here.
To choose the correct converter, here are the most important parameters:
You can make an easy first selection by checking the first parameters under here yourself. Of course, Elipse can always support on defining the best solution.
Input voltage: this parameter is defined by the power source used. Different power sources (for instance, AC-DC adapters or batteries) provide different input voltages. When designing electronics, a hardware development company must make sure the DC-DC converter can withstand these voltages.
Output voltage: DC-DC converters can produce either fixed or adjustable output voltage. The latter can vary from a minimum to a maximum value. In both cases, the choice of models is defined by the voltage range required by the load.
Output current: output current (along with the output voltage) defines the electrical power that a converter can provide.
Efficiency: efficiency is the percentage of the input power delivered to the output. As mentioned above, the efficiency of DC-DC converters can vary a lot. For example, if the device is powered by batteries, the efficiency defines how long the device can work before you have to replace them. Efficiency is an important parameter. In some cases, efficiency itself is not as important. However, the energy lost during conversion dissipates as heat. This in turn can lead to undesirable consequences.
Temperature: since extra energy goes into heat, overheating can become a serious issue. This problem can be partially solved with proper casing. But in certain cases, one may have to use additional thermal protection.
Size and mounting types: DC-DC converters are available in many package types. If it needs to be mounted into a PCB, designers can choose from a variety of mounting styles, including smd or through-hole mounting. The size also matters when you develop small devices.
Stable supply: finally, when picking converters for a device, it’s also important to make sure the manufacturer will not stop supporting the model in the near future. That’s why the Elipse team always gives priority to the latest models.
EMC Issues: electromagnetic compatibility is one of the most important issues you may face when using DC-DC converters. Due to higher efficiency, switching types are very popular. However, as mentioned above, they generate electromagnetic noise. Therefore, such devices must be tested for electromagnetic compatibility to make sure they don’t cause electromagnetic interference effects on other devices.
The Elipse team can support you here with reviewing your design but we also have recommended lay-out schematics available for you to pass the test and make your life as easy as possible.
Safety Issues: when the difference between the input and output voltages can reach many volts, this can be extremely dangerous. Therefore, equipment using high-voltage (HV) DC-DC converters must meet safety requirements. Safety requirements are regulated by different standards, with the most common being IEC 60950-1 for Information technology equipment, IEC 60335-1 for electrical appliances for household and similar purposes, and IEC 60601-1 for medical electrical equipment. Note that national standards are based on International Electrotechnical Commission’s standards but may contain deviations.
Functional Insulation: the functional insulation between the input and output circuits is only required for the proper work of the device. However, it does not provide enough protection from electric shock if the input-to-output insulation suffers a breakdown or fault. This level of protection must meet at least one of the standard’s requirements sets:
- Clearance and creepage distances
- Electrical strength tests
- Fault condition testing
A device’s DC-DC converter is allowed to have functional insulation if:
- The AC-DC power supply uses reinforced or double insulation between the AC input and DC output.
- The AC-DC power supply uses basic or supplementary insulation, while the secondary circuit of the DC-DC converter connects to protective Earth.
- The AC-DC supply has basic or supplementary insulation, while the primary circuit of the DC-DC converter connects to protective Earth.
Basic Insulation: this insulation grade provides basic protection against electric shock. Devices must meet all three sets of requirements. This level is required if the AC-DC power supply has functional insulation between the AC input and DC output, while the secondary circuit of the DC-DC converter connects to protective Earth.
Supplementary Insulation: beside meeting the basic insulation requirements, this grade adds one more level of protection, such as increasing the distance through insulation by 0.4 mm for peak voltages above 71V. This level of protection is required if the AC-DC power supply uses basic insulation between the AC input and DC output.
Double Insulation: this protection level combines basic and supplementary insulations.
Reinforced Insulation: it’s a single insulation system capable of providing the same protection grade as double insulation. It can comprise several protection layers and is required if the AC-DC power supply has no insulation or functional insulation between the AC input and DC output.
Support on your design: at Elipse we can always help you with the best choice for your design. We know the “hard runner products” for now and in future, this gives you good basics for price and availability for the complete life-cycle of your product. We can support you with EMC related questions, together with our partners we can review your design and always give you advice on optimizing the performances of your product. Please let us know when you are looking for certifications for your components, we are always willing to serve you.
Gaia DC/DC converter MGDM-04: 4W power
The MGDM-04 series is a full family of high performance and low profile DC/DC power modules designed for aerospace, military and high-end industrial applications. These modules use a high frequency fixed switching technic at 480KHz providing excellent reliability, low noise characteristics, high power density and a low profile package. Standard models are available with nominal input voltages as 5, 12 or 28 volts in range of 4,5-5,5 , 9-36 or 16-40 volts. The series include single, bi and triple output voltage choices of 3.3, 5, 12, 15, +/-5, +/-12 or +/-15 volts. No external heatsink is required for the MGDM-04 series to supply 4W output power over the case temperature range of -40°C up to 105°C. All the modules are designed with LC network filters to minimize reflected input current ripple and output voltage ripple.
Mornsun: B_S-1WR3 Series
A very common and competitive serie from Mornsun you find in this range from Mornsun with 1W isolated DC-DC converter Fixed input voltage, unregulated single output.
Continuous short-circuit protection. No-load input current as low as 8mA. Operating ambient temperature range:-40℃ to +105℃. High efficiency up to 81%l I/O isolation test voltage: 1.5kVDCl Industry standard pin-out.
These components relative short lead times and are offered for competitive pricing. We have no MOQ and can support you with much information on products and design. Be impressed from all the opportunity’s Elipse can offer you here.
