Information About DC power supply

What is A DC Power Supply?

An AC powered unregulated power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to produce DC, a rectifier is used to convert alternating voltage to a pulsating direct voltage, followed by a filter, comprising one or more capacitors, resistors, and sometimes inductors, to filter out (smooth) most of the pulsation. A small remaining unwanted alternating voltage component at mains or twice mains power frequency (depending upon whether half- or full-wave rectification is used)—ripple—is unavoidably superimposed on the direct output voltage. For purposes such as charging batteries the ripple is not a problem, and the simplest unregulated mains-powered DC power supply circuit consists of a transformer driving a single diode in series with a resistor. Before the introduction of solid-state electronics, equipment used valves (vacuum tubes) which required high voltages; power supplies used step-up transformers, rectifiers, and filters to generate one or more direct voltages of some hundreds of volts, and a low alternating voltage for filaments. Only the most advanced equipment used expensive and bulky regulated power supplies.

How does A DC power Supply work?

1.AC Power In

  • When power comes into a building, it is in AC, or "alternating current." AC current switches back and forth from positive to negative 60 times a second. It is carried into the building on the live wire. A second wire, called the return wire, carries the current back out of the house to complete the circuit.
  • AC current is carried in at 120 volts, far too high a voltage for most DC appliances. The voltage must be reduced through a step-down transformer. The AC current runs through a coil, which creates a magnetic field. A second coil, with fewer turns of wire, is placed next to it. The magnetic field from the first coil creates an electric current in the second coil. Because there are fewer turns in the second coil, it creates lower-voltage AC electricity.
  • Unlike AC, DC, or "direct current," only flows in one direction. A DC power supply has two wires--one with a negative charge and the other with a positive charge. A device called a rectifier is used to turn AC into DC. The central component of a rectifier is the diode. Diodes are one-way electric valves. When the electricity in the circuit turns negative, a diode lets it flow down the negative wire. When the electricity cycles back to positive, that diode closes automatically, and another diode lets the positive current flow down the positive wire. There are several different types of rectifiers, but they all use diodes in essentially the same way to separate the negative current from the positive.

Reducing the Voltage

  • AC current is carried in at 120 volts, far too high a voltage for most DC appliances. The voltage must be reduced through a step-down transformer. The AC current runs through a coil, which creates a magnetic field. A second coil, with fewer turns of wire, is placed next to it. The magnetic field from the first coil creates an electric current in the second coil. Because there are fewer turns in the second coil, it creates lower-voltage AC electricity.

Making DC

Unlike AC, DC, or "direct current," only flows in one direction. A DC power supply has two wires--one with a negative charge and the other with a positive charge. A device called a rectifier is used to turn AC into DC. The central component of a rectifier is the diode. Diodes are one-way electric valves. When the electricity in the circuit turns negative, a diode lets it flow down the negative wire. When the electricity cycles back to positive, that diode closes automatically

How To Use a DC power Supply?

Testing a low-voltage direct current (DC) power supply is something any moderately experienced electronics hobbyist or technician can handle. The supply's job is simply to provide reliable voltage and current within its specified limits. You can check most power supplies with a pair of multimeters and a dummy load. The voltage should be clean and steady, not dropping when you put a moderate load on it. If the supply has poor voltage with no load, or if the voltage drops excessively with a load, it needs to be repaired. 1-Set one multimeter to read DC voltage. Connect its black (negative) probe to the power supply's output ground. Connect the meter's red (positive) probe to any positive power output. Turn the power supply on and observe the voltage on the meter. If the supply has multiple outputs, positive or negative, touch the red probe to each one and compare the meter's reading to the supply's rated output. If the output voltage is variable, turn the supply's voltage control up and down and check the results on the meter. If the meter reads a voltage that's more than a few percentage points high or low, the power supply is defective. 2-Select a dummy load based on the power supply's specifications by using Ohm's Law. The dummy load can be a power resistor rated to handle the supply's maximum output. For example, a power supply that's rated for 10 volts and 1 amp needs a resistor of at least 10 volts times 1 amp = 10 watts. To make sure it's using 1 amp, you want the resistance to be 10 volts / 1 amp = 10 ohms. A 10 ohm, 20 watt resistor would be a good choice. 3-Turn the supply off. Set another multimeter to read current in amps. Connect its black probe to the supply ground and the red probe to one lead of a dummy load. Connect the dummy load's other lead to the appropriate power supply output. Connect the red lead of the first multimeter (set to read voltage) to the same positive supply output. Turn the supply on and compare the current and voltage readings on the meters with the supply's specified output. Let the supply run for a few minutes and check to see if the voltage drops. If the voltage was reading fine in step 1 but now reads too low, the supply has poor regulation.

Tips & Warning

DC power supplies are powered by 110-volt household alternating current (AC). This higher voltage will be present at the power cord connection and the supply's step-down transformer. Never touch these parts with your fingers or uninsulated metal tools unless the supply is unplugged from the wall. Other Models… Need More Information:

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Power by How It Work

20th Jan 2015

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