Fundamentals Of Power Supply Design Download
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As shown above, power supply circuits are basically used to change energy from one state to the other, AC to DC or vice-versa, to change levels, raise or lower voltage, or frequency. AC-AC power supplies may also be used to isolate input circuits from outputs. In addition to the types above, power supply circuits can be categorized as either regulated or unregulated. Regulated power supplies include devices to maintain the output voltage level. These voltage regulators are not present in unregulated power supplies and the output varies with the input and changes in load current.
The Linear power supply above is used to convert a mains AC input, the primary side of transformer TR1, into DC for distribution. This circuit includes a voltage regulator, IC1, that will provide a constant voltage irrespective of the load, R1. This linear power supply demonstrates the basic operation of these circuits, which may have many different configurations. Linear power supplies are typically used in lower power systems. The advantages are their simplicity, low cost, reliability, and low noise; however, they are inefficient which becomes more of a concern in higher power applications.
An SMPS power supply contains switching circuitry; such as transistor T1 above, that converts the rectified DC from the bridge circuit, B1, into high-frequency AC. The frequency level is determined or set by the control signal that turns the transistor on and off. In the circuit above, the output is smoothed or regulated by the LC filter before being applied to the load, R1. Typically, SMPS circuits are more complex than linear power supplies and the switching introduces noise that can create EMI which may affect your trace routing during PCB layout. However, these power supplies are more efficient and can utilize smaller components than linear power supplies. SMPSs are most often for digital systems.
When designing an SMPS or a linear power supply circuit board, there are common areas of concern. These include thermal considerations, EMI or noise and depending on power level copper weights. Another important consideration is the power supply filter design. Although your specific design requirements will dictate specific design choices, there are general fundamentals of power supply design for PCBs that should always be followed, as listed below.
By instituting the fundamentals listed above into power supply design process you will be able to identify and address areas that significantly the manufacture of your boards. Tempo Automation, the industry leader in fast, high-quality PCB prototype and low-volume manufacturing, can assist you in ensuring that design meets all the requirements for the best construction of your boards.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on the fundamentals of power supply design for circuit boards, contact us.
Power is the backbone of any electronic system and the power supply is what feeds the system. Choosing the right supply can be the critical difference between a device working at optimum levels and one that may deliver inconsistent results.
In addition to alternating current (AC) to direct current (DC) power supplies, DC to DC converters are also available. If DC is already available in your system, a DC to DC converter may be the better design choice than AC discussed below.
A power supply takes the AC from the wall outlet, converts it to unregulated DC, and reduces the voltage using an input power transformer, typically stepping it down to the voltage required by the load. For safety reasons, the transformer also separates the output power supply from the mains input.
The capacitor is typically quite large and creates a reservoir of energy that is applied to the load when the rectified voltage drops. The incoming energy is stored in the capacitor on the rising edge and expended when the voltage falls. This significantly reduces the amount of voltage droop and smooths out the voltage. Increasing the storage capacity of the capacitor generally produces a higher quality power supply.
Once the voltage conversion is complete, there is still some variation in output, called ripple. In a regulated power supply, the voltage is then passed through a regulator to create a fixed DC output with less ripple.
AC power supplies come in two varieties, unregulated and regulated. Unregulated is the most basic type of power supply and does not have the ability to supply consistent voltage to a load, while regulated power supplies do and have many different design options.
AC is also called mains electricity, household current, domestic power, line power, or wall power because it is the voltage supplied by a wall outlet. Worldwide, AC voltages range from 100 to 240 V. The rate of direction change is typically 50 to 60 times per second and is designated as Hertz (Hz). The two most common frequencies are 50 Hz and 60 Hz.
With an unregulated DC power supply, the voltage output varies with the size of the load. It typically consists of a rectifier and capacitor smoothing, but no regulation to steady the voltage. It may have safety circuits and would be best for applications that do not require precision.
A regulated DC power supply is essentially an unregulated power supply with the addition of a voltage regulator. This allows the voltage to stay stable regardless of the amount of current consumed by the load, provided the predefined limits are not exceeded.
There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages.
Switched Power SupplySwitched mode power supplies (SMPS) are more complicated to construct but have greater versatility in polarity and, if designed properly, can have an efficiency of 80% or more. Although they have more components, they are smaller and less expensive than linear power supplies.
The advantages of a switched power supply is that they are typically small and lightweight, have a wide input voltage range and a higher output range, and are much more efficient than a linear supply. However, a SMPS has complex circuitry, can pollute the AC mains, is noisier, and operates at high frequencies requiring interference mitigation.
Battery-basedBattery-based power is a third type of power supply and is essentially a mobile energy storage unit. Battery-based power produces negligible noise to interfere with electronics, but loses capacity and does not provide constant voltage as the batteries drain. In most applications using laser diodes, batteries are the least efficient method of powering the equipment. Most batteries are difficult to match the correct voltage to the load. Using a battery that can exceed the internal power dissipation of the driver or controller can damage your device.
Along with the above considerations, the power supply must operate below its maximum rated output current. Loads drawing more current than the adapter is rated for can cause inconsistent results or device malfunction. Overloading the converter can lead to overheating and ultimately failure, potentially causing a fire hazard or damaging the load itself.
Overvoltage Protection: Sometimes output voltages can exceed their nominal values and can damage the load. Overvoltage protection is a circuit that shuts down the power supply should the voltage limits be exceeded.
Overload Protection: Overload protection is a safety measure used to prevent damage in the event of a short circuit or overcurrent event. Much like the circuit breaker in a house, the overload protection shuts off the power supply so the load will not be damaged.
Efficiency: Efficiency is the ratio of power being pulled from the power grid that is effectively being converted to DC power. A good SMPS power supply will operate with at least 80% efficiency and, with a proper system design, can operate at even higher rates. An efficient system will reduce heat generation and can save energy.
Noise is the unwanted additions that occur outside of the normal ripple. It comes from many other sources, including switching and electronic noise generated outside of the power supply, such as from nearby electronics. Noise usually occurs in conjunction with ripple and is much more variable and unpredictable. Switching noise typically occurs at very high frequencies.
Figure 8 illustrates the noise potential in a regulated linear power supply. While much less than the ripple of a regulated switched supply, it can still be significant enough to mask data. If the noise and ripple are very high, small signals can be overwhelmed or the life of the hardware can be significantly shortened. However, with a high quality power supply it can be virtually eliminated.
At the advent of electrical distribution, the standard current in Europe was alternating current (AC) and in the US was direct current (DC). The main load of electrical usage was the light bulb, which was designed by Thomas A. Edison to use direct current. The early competition between which electrical distribution system would dominate the market in the US was called The War of Currents and was typically personified as a conflict between inventor Edison (Con Edison/General Electric) and entrepreneur George Westinghouse (Westinghouse Electric), who invested in the AC technology as a power distribution method. The conflict was actually much larger, with American and European companies having a vested interest in the decline of one type or the other. 2b1af7f3a8