## Diode bridge rectifier circuit

Diode bridge rectifier's circuit is a full-wave rectifier circuit that uses four diodes, and connected as a bridge. Unlike the full-wave rectifier discussion in previous article, where the circuit uses two diodes, this time is full-wave rectifier circuit with four diodes.

Beside different from amounts of diodes, other difference lies in use of a transformer, which transformer used in the bridge rectifier circuit system is not a transformer which has ct (center tap) or using a conventional transformer without ct.

Diode bridge rectifier's circuit as shown below

which:
• AC = AC voltage source
• D1, D2, D3, D4 = diode rectifier
• C = electrolyte capacitor
• RL = Load

## Transistor as a switch

One function of transistor most commonly used in the electronics world is as a switch. To find out how transistor as a switch, we do experiments on the following circuit.

Switch (S1) condition in Off state or open, there is no voltage source attached to the base terminal of transistor, so that there will be no current flowing in the circuit, in other words, the lamp will not light.

Switch (S1) condition in On state or closed, voltage source is attached to the base terminal of transistor, so that there will be currents flowing in the circuit, in other words, the lamp will turn on.

## How transistors work

If there is no external voltage is connected to transistor, then there is no current flowing in a circuit, in other words all the electrical current equal to zero. So to use a transistor, we need to link in such a way, to obtain a current flow that we want.

Circuit below is an example of how the NPN transistors work

where:
1. Emitter terminal is a negative polarity
2. Collector terminal has a few volts more positive than emitter terminal
3. Base terminal is 0.7 Volt more positive (see break down voltage) or greater.

With these conditions, we can see that:
• A relatively small current flows through the base (IB)
• Currents with a much greater value flow through the collector (IC)
• Base current and collector current flowing out of transistor through the emitter.

## Determine terminals and type of transistor using analog multimeter

Almost all of analogue multimeter or AVO meter (Ampere, Volt and Ohm meter, as shown in the figure below), can use to determine terminals (base, emitter, and collector) and type of transistor (PNP or NPN). On this configuration, turn the knob multimeter's position on Ohm meter test or at symbol Ω.

We take an example to be measured is transistor BJT type FCS9015, which is quite widely use. We learned to determine terminals and type of transistor FCS9015, and the following steps:
1. Measuring and create tables of measurement
• Set analogue multitester and adjust position of rotary knob on Ohm meter, a measurement scale at x10
• Imagine or describe the position of terminals transistor with sequence numbers 1, 2, and 3
• Create a table with 6 units of measurement measuring point, ie 1-2, 1-3, 2-3, 2-1, 3-1, and 3-2
• Specify black probe or negative test probe for the first number, and red probe or positive test probe for the second number, ie the measuring point 1-2, the black probe at point 1, and the red probe at point 2
• Record the results of each measurements, indicated by Ohm meter's needle movement

2. Determine base terminal and type of transistor
On the measurements table, there are two measurement points that get results, that is point 1-2 and point 3-2 (see figure above). It is time for us to determine the terminals and type of transistor, by the way:
• Base is the same number found on the two measuring points
• Type NPN or type PNP, we can set it to see what probe is connected to the base. If base point connected to black probe, then NPN type transistor, and when base point connected to red probe, then PNP type transistor
There is different probe usage between analog multimeter and digital multimeter. In the analog multimeter, red probe is connected to negative battery Ohm meter, and black probe is connected to positive battery Ohm meter

3. Determine emitter and collector terminals of transistor
Needle's moves at measurements points 1-2 and 3-2, almost have equal value, so it will be difficult to determine terminals collector and emitter using analogue meter. So we use a manual way, ie with visual or sight. There are several characteristics that indicate the collector's terminal, among others:
• The letter C is printed larger
• There is a little hole
• Generally connected to the metal on packaging or transistor's body, especially at high power transistor body

We've been able to determine base and collector of terminals transistor, then last is emitter terminal.

So we get the conclusion:
1. At point 2 terminal base of transistor FCS9015
2. FCS9015 is a PNP transistor, the base on red probe
3. At point 3 terminal collector FCS9015, see! there is letter C is printed larger
4. At point 1 terminal emitter of transistor FCS9015
5. Terminals and type of transistor FCS9015 as shown in the picture below

How to determine terminals base, emitter and collector of transistor using digital multimeter? just click that link.

## How to determine terminals and type of transistor using digital multimeter?

Requirement to determine terminals (base, emitter, and collector) and type (PNP or NPN) transistor using an AVO meter or multimeter or digital multitester, is multitester must have a diode test feature. Diode test feature is usually denoted by symbol of a diode, as shown in multitester's picture below.

We take an example to be measured is transistor type C945, which is quite widely use. We learned to determine terminals and type of transistor C945, and the following steps:

1. Measuring and create tables of measurement
• Set Multitester the rotary knob of multitester on diode test feature
• Imagine or describe the position of terminals transistor with sequence numbers 1, 2, and 3
• Create a table with 6 units of measurement measuring point, ie 1-2, 1-3, 2-3, 2-1, 3-1, and 3-2
• Specify black probe or negative test probe for the first number, and red probe or positive test probe for the second number, ie the measuring point 1-2, the black probe at point 1, and the red probe at point 2
• Record the results of each measurements

2. Determine terminals and type of transistor
On the measurements table, there are two measurement points that get results, that is point 1-3 at 0.720 VDC, and point 2-3 at 0.716 VDC (see figure above). It is time for us to determine the terminals and type of transistor, by the way:
• Base is the same number found on the two measuring points
• Type NPN or type PNP, we can set it to see what probe is connected to the base. If base point connected to black probe, then PNP type transistor, and when base point connected to red probe, then NPN type transistor
• Emitter-Base forward bias greater than Collector-Base, or EB > CB, that is PNP type transistor. Base-emitter forward bias greater than Base-Collector, or BE > BC, that is NPN type transistor

So we get the conclusion:
1. At point 3 the transistor base C945
2. C945 is a NPN transistor, the base on red probe
3. At point 1 terminal emitter and at point 2 terminal collector C945, because the point 1-3 > 2-3
4. Terminals and type of transistor C945 as shown in the picture below

## Transistor, bipolar and unipolar

Transistor is an electronic component semiconductor, has ability to control the effective resistance by controlling the main signal (voltage and amperage) from a distance.

There are two types of transistors, namely a bipolar junction transistor or abbreviated by BJT, such as PNP and NPN, and unipolar transistor junction transistor or abbreviated by UJT, such as FET and MOSFET.

Transistors made from crystalline silicon or germanium, where a layer of N type silicon layer sandwiched by two types of P. Conversely it could also be made transistor consisting of two N-type silicon layers sandwiching a layer of type P. Both transistors are kind of BJT transistor, or PNP and NPN type.

In general, BJT transistor has three terminals, ie base (abbreviated with the letter B), collector (abbreviated with the letter C), and emitter (abbreviated with the letter E).

Below is a symbol of PNP and NPN transistor