A benchtop power supply is an essential component of any electronics development, test, or repair laboratory bench. Engineers, technicians, and educators need a reliable source of DC power to test and develop a variety of circuits under the required conditions. DC power supplies are required to convert AC power into regulated DC power to drive ICs and other electronic components. There are two types of DC benchtop power supplies: linear and switch-mode, or “switching” power supplies.
The buck converter is a very simple type of DC-DC converter that produces an output voltage that is less than its input. The buck converter is so named because the inductor always “bucks” or acts against the input voltage. The output voltage of an ideal buck converter is equal to the product of the switching duty cycle and the supply voltage. Like many power supply topologies, the buck converter operates on the principal of storing energy in an inductor. The voltage drop across an inductor is proportional to changes in electric current flowing through the device.
Flyback converters are one of the simplest DC-DC converter topologies to include electrical isolation. Although generally only viable for lower range power supplies (up to 100W), they do have a number of advantages. Other than the converter’s inherent simplicity, perhaps the greatest of these is that the design does not require an additional inductor. The transformer provides isolation, and yet also functions as a pair of coupled inductors, storing energy as with a basic buck or boost converter. (Replacing the transformer with a series inductor will, in fact, give us the boost converter topology.)
A forward converter is a type of DC-DC converter that, like the flyback and half-bridge converters, can supply an output voltage either higher or lower than the input voltage and provide electrical isolation via a transformer. Although more complex than a flyback, the forward converter design can yield higher output power (generally up to 200W) along with higher energy efficiency.
A half-bridge converter is a type of DC-DC converter that, like flyback and forward converters, can supply an output voltage either higher or lower than the input voltage and provide electrical isolation via a transformer. Although more complex than a flyback or forward converter, the half-bridge converter design can yield higher output power (potentially up to 500W) and use parts that are smaller and less expensive.
Power dissipation is highly dependent on operating temperature, the semiconductor process used, operating frequency, level of activity, and operating voltage. An extra power management device can be worth the initial cost and be worth the extra space taken up by reducing overall power consumption of a design, as well as provide better operation. This is where the trade-off is “real estate” for watts. For example, a Low Drop Out Regulator (LDO) halts power consumption by switching off unneeded functions. Besides judicious application of devices for managing consumption, power management devices themselves have enable/disable pins, sleep states, soft-start features that limit in-rush current, and shutdown modes that still draw a trickle of current, yet allow a rapid wake up. Low quiescent current and a low forward voltage drop are key desired attributes in selecting an LDO for ultra low power applications.
Compared with linear supplies, switched-mode power supplies (SMPSs) not only provide a substantial boost to energy efficiency but are also smaller and lighter – advantages that have seen SMPSs completely replace their linear counterparts in many applications.
A transformer is a magnetic component made up of two or more windings of copper wire with a core running down the middle of these windings. The windings are insulated from each other but in very close proximity. It transfers electrical energy from one electric circuit to another, without changing the frequency by via a magnetic field. The transfer usually takes place with a change of AC voltage and current. Its main function in power applications is to transform incoming AC voltage from your outlet, typically 110V to 120V, down to a voltage level that your end products can use.
An uninterruptible power supply (UPS) is an electronic device that supplies emergency power in the event of a power fault or power failure. A UPS device is different from an auxiliary power system in its ability to deliver backup power instantaneously. Capable of providing only short-term power, UPSs are often used to power an electronic system just long enough for an auxiliary power system to come online or, failing that, allow for the equipment to be properly shut down.