Switch Mode Power Supplies (SMPS)
Switch mode power supplies are much more efficient than linear power supplies and are available from very lower power (1W) through mass market (around 50-300W) and high power units above 1KW. AC/DC switch mode power supplies convert alternating current (e.g. Mains electricity) into a stable DC voltage. DC/DC converts either increase or reduce the input voltage to provide a new output voltage level.DC/DC converters are often used for converting a battery power source (e.g. car battery) to a stable DC output voltage to power some electronics. As the battery voltage may vary between 9 and 16V DC, the output voltage remains stable.
Both AC/DC and DC/DC power supply types may have one or more output voltages. Single outputs are commonly 3.3V, 5V, 12V and 24V. Dual output power supplies are usually configured as 5V/12V, 3.3V and 5V or dual +12V/-12V.
Each output has a maximum available output current Iol and for multi-output power supplies each output voltage may have a different value for the maximum output current. For instance, a power supply may have a main output at 3.3V @ 100W but a secondary output of 5v but at only 10W.
Many power supplies also have protection circuits which protects them against overload. Power supplies may exhibit foldback (output voltage drops when maximum output current exceeded) or it may have a current limiter which keeps the output voltage at the required level but allows no more current to flow (ideal for battery charging).
Higher power power supplies will require fan cooling which is potentially a failure point as fans are mechanical devices which wear out over time. Lower power units will normally work with convection cooling or by being bolted down to a thermal heatsink.
High Voltage Power Supplies
High voltage power supplies may be AC/DC or DC/DC in design but have very high voltage outputs (typically 1KV or higher)
Dual Redundant Switch Mode Power Supplies
Where the power has to flow constantly 24/7/365 engineer make use of dual redundancy power supplies. In the event of a failure of one of the power supplies, another identical power supply will automatically take over the load which the faulty unit can be replaced.
Dual redundant power supplies may work by load sharing (e.g. each power supply supplies only 50% of the required output power).
Power Supply Monitoring and Control
Modern switch mode power supplies include external monitoring and control features. Remote control is available in the form of an input which may enable/disable certain outputs or put the power supply into a low power 'sleep' mode.
Remote monitoring can test the output voltage is within a required range and provide a relay output if the output voltage is out of range. Overload, over voltage and other errors can also be signalled.
Bench Power Supplies
Bench power supplies are switch mode power supplies where the user has fine control over the output voltage and current limit. These are used by electronics/electrical engineers and scientists in design and testing of products. Bench power supplies usually have an LED read out to show the current limit and output voltage and have one or more output voltage.
Linear Power Supplies
One of the big disadvantages of switch mode power supplies is all of the switching causes electrical noise. For applications which require very low noise outputs a linear power supply is preferable.
Linear power supplies are typically available up to 200W maximum and may have dual output +/-12V for instance.
Find a Switch Mode Power Supply Manufacturer
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