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About DC
About DC
Direct current (DC) is one-directional flow of electric charge. When a constant emf is applied across a network of conducting components there will be a short period during which the current will increase from zero to a steady value. The resultant steady current is referred to as a direct current and the theory of such currents is referred to as dc theory or dc network theory.
History
History
Starting in the late 1880s, Thomas Edison and Nikola Tesla.
Edison developed direct current -- current that runs continually in a single direction, like in a battery or a fuel cell.
Figure left is showing the symbol and on the right is the dc wave form.
Basic diagram DC supply.
Safety Hazard
Safety Hazard
Both AC or DC currents can cause fibrillation of the heart at high enough levels. This typically takes place at 30 mA of AC (rms, 60 Hz) or 300 – 500 mA of DC. AC and DC currents and shock are lethal, more DC current is required to have the same effect as AC current.
Danger : More energy released from +vDC therefore when metal contacted with +ve , arcing is formed like welding.
WARNING
WARNING
1. DC voltage are dangerous where a simple cross over a objects, wire or any other conducting material may give rise to the voltage and current. When these current flow through the object, it becomes hot and may cause fire any moment of time.
2. Wrong polarity may damage your electronic equipment. Batteries have positive (+) and negative (-) terminals. If you take a wire and connect the positive and negative terminals on a battery, the electrons in the wires will begin to flow to produce a current.
3. DC voltage can kill a living person (>24 volts DC) depending on how it is been contact between victim and the DC supply source. Therefore always wear PPE such as rubber gloves before handling DC supply.
Components to produce direct current
Components to produce direct current
The following component to make direct current.
AC input voltage
Transformer - to lower the voltage
Rectifier - to change the supply from AC to DC
Filter circuit - to smoothen the DC output .
1. Transformer
1. Transformer
This induction device design to lower the voltage input so that the output voltage can be usable for loads and equipment that connected to the DC supply.
The transformer takes AC voltage as inputs and the output induced voltage ( or secondary voltage, Vs ) must be identified to suit the correct voltage to any loads required.
3V, 5V, 9v, 12v (for small electronics or signal process)
24v, 36v, 48v and 96v (for power electronics and controls)
Figure above is an AC Transformer .
Primary: 220~240vAC Secondary: 12 volts ACFor reference
Figure above showing an alternating current (AC) sine wave.
2. Rectifier circuit
2. Rectifier circuit
The rectifier circuit is used in DC makings basically converting the AC wave form to DC wave form. This concept can change the voltage source from AC to DC with just four(4) simple diodes connected in bridge figure below.
Figure diode (semiconductor device)
Figure above is the configuration known as bridge circuit.
For reference
Figure above showing rectifier device.
D1, D2 will change the -V (bottom wave) to up +V side.
D3, D4 will change the -V (bottom wave) to up +V side.
Figure above is the output wave from rectifier circuit (D1,D2,D3,D4) before going to next stage.
3. Filtering Circuit
3. Filtering Circuit
DC wave form is not smooth and filtering is required. The filter circuit is to smoothen the DC wave form. Capacitor is installed to the circuit, this filter reduce the ripple effect.
There are two types of filter circuit.
RC filter
LC filter
i. LC filter
i. LC filter
LC Filter circuit - basically using a inductor device and capacitor is final smoothing the wave form.
This filtering helps to improve and stabilize the current flow in circuit.
Figure above showing LC filter.
ii. RC filter
ii. RC filter
RC filter circuit - basically using a resistor and capacitors to final smoothing the wave form.
This filter can stabilized the output voltage.
Figure above showing RC filter.
Figure above showing the output wave form of going through a capacitors. The red color lines is known as ripple voltage (not yet stable).
Ripple voltage can be solved by adding more capacitors and will smoothening the DC output waveform.
Figure above showing the final output DC wave form
DC applications
DC applications
DC application in today modern technology are vast and highly in demand.
charging batteries,
automotive applications,
aircraft applications
electronics gadgets, toys
DC motors and machinery
control circuits
DC supply generators
DC supply generators
There many ways to generate direct current in today modern science technology.
mixture of chemicals - such as batteries
taking light from sunlight - solar power
mechanical moving part - alternator or dynamo
Measuring transformer
Measuring transformer
Basically transformer consist of four(4) terminals:
Primary side (incoming AC supply) - T1 (L) , T2 (N) while
secondary side is labeled T3, T4 (both are known as induced voltage).
How to check transformer is GOOD or BAD?
How to check transformer is GOOD or BAD?
We can check the conditions transformer by using continuity test. This test basically is to measured the resistances of the both primary and secondary. You can use analog or digital multi-meter to perform the checking conditions of transformer.
Primary side of a typical transformer if it is step down voltage transformer the resistance coil is measured higher Ω compare to secondary terminals. Therefor most step down voltage transformer are expected to be high ohm range.
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