Diodes force the current to flow in only one direction, like a one-way valve, general function of diode is for rectifier and alternating current protection.
Diodes have a negative lead (-) and a positive lead (+), which are called the cathode and the anode, respectively.
If the anode is at a higher voltage than the cathode (it has two be greater by about half a volt), it conducts electricity, and we say that it is "forward-biased". If not, we say that it is "reverse-biased" and the current doesn’t flow.
Diode with Three Leg:
SMD Dual Diode is a single package with 2 diodes, middle pin is the negative. As a switch control in circuit, the form and function it’s like a transistor, but it’s different. This Three leg diode function in motherboard laptop is for circuit protection and helping the transistor.
Diode Zener:
Zener Diodes will be has the characteristics and functions as normal diodes in general, but on laptop motherboard diode zener lot on use for voltage stabilizer.
Zener diode symbol on the circuit diagram and motherboard usually begin with letter "D, PD and ZD".
LED Diode:
The function of LED diode in motherboard laptop is almost 95% for light indicator. Because power consumption is very low, lot of product motherboard using SMD diode LED type, LEDs have polarities. If you take a close look at an LED, you’ll see that it has two distinct legs (also called leads). One lead is longer than the other, longest lead Anode (+) shortest lead Cathode (-), Examples are the LEDs of the power button, battery, etc.
How to test a Diode:
Before testing a diode, we must know the diode terminals like Anode (+) and Cathode (-). In most cases, there is a white band color coating on normal PN junctions diodes which indicates as cathode terminal and the rest is anode. In other cases, there are different colors are used and the color coated sides are cathode as shown in photo below.
Below is a tutorial that shows how to test a normal PN Diode, LED and Zener Diode by different methods.
Testing Diode using (Diode Test Mode + Resistance Mode):
Set the meter on "Diode Test" Mode and connect the diode leads to the multimeter test leads and note the reading.
Forward Biased:
When the positive (Red) test lead is connected to the anode (+) and negative (Black) test lead is connected to the cathode (-) of diode. In Forward-biased, the diode acts like close switch and will pass the current through it like conductors.
Reverse Biased:
If we do the reverse as mention above Red Test lead to cathode (-) and Black test lead to the Anode (+) of the diode. In revere-biased, the diode acts like open switch and will not let pass the current through it like resistor.
If multimeter display "OL" in reverse biased, it is good as well.
If multimeter display "OL" reading in both direction (Forward-biased and reverse biased), its mean diode is dead and acting as an open switch which doesn’t allow current to flow in it, in case of shorted diode.
How to test LED (Light Emitting Diode):
Set the meter on "Diode Test" Mode and connect the positive probe to cathode and the negative probe to anode. If LED doesn't light up, reverse the test probes, the good and working LED will then light up or glow, a busted LED will not.
How to test Zener Diode:
As we have discussed that the Zener operates same as a common diode so the diode test mode method will be the same for Zener. Set meter to diode test range and you should expect reading one side and when you reverse the probes you will get no reading.
Diodes have a negative lead (-) and a positive lead (+), which are called the cathode and the anode, respectively.
If the anode is at a higher voltage than the cathode (it has two be greater by about half a volt), it conducts electricity, and we say that it is "forward-biased". If not, we say that it is "reverse-biased" and the current doesn’t flow.
Diode with Three Leg:
SMD Dual Diode is a single package with 2 diodes, middle pin is the negative. As a switch control in circuit, the form and function it’s like a transistor, but it’s different. This Three leg diode function in motherboard laptop is for circuit protection and helping the transistor.
Diode Zener:
Zener Diodes will be has the characteristics and functions as normal diodes in general, but on laptop motherboard diode zener lot on use for voltage stabilizer.
Zener diode symbol on the circuit diagram and motherboard usually begin with letter "D, PD and ZD".
LED Diode:
The function of LED diode in motherboard laptop is almost 95% for light indicator. Because power consumption is very low, lot of product motherboard using SMD diode LED type, LEDs have polarities. If you take a close look at an LED, you’ll see that it has two distinct legs (also called leads). One lead is longer than the other, longest lead Anode (+) shortest lead Cathode (-), Examples are the LEDs of the power button, battery, etc.
How to test a Diode:
Before testing a diode, we must know the diode terminals like Anode (+) and Cathode (-). In most cases, there is a white band color coating on normal PN junctions diodes which indicates as cathode terminal and the rest is anode. In other cases, there are different colors are used and the color coated sides are cathode as shown in photo below.
Below is a tutorial that shows how to test a normal PN Diode, LED and Zener Diode by different methods.
Testing Diode using (Diode Test Mode + Resistance Mode):
Set the meter on "Diode Test" Mode and connect the diode leads to the multimeter test leads and note the reading.
Forward Biased:
When the positive (Red) test lead is connected to the anode (+) and negative (Black) test lead is connected to the cathode (-) of diode. In Forward-biased, the diode acts like close switch and will pass the current through it like conductors.
Reverse Biased:
If we do the reverse as mention above Red Test lead to cathode (-) and Black test lead to the Anode (+) of the diode. In revere-biased, the diode acts like open switch and will not let pass the current through it like resistor.
If multimeter display "OL" in reverse biased, it is good as well.
If multimeter display "OL" reading in both direction (Forward-biased and reverse biased), its mean diode is dead and acting as an open switch which doesn’t allow current to flow in it, in case of shorted diode.
How to test LED (Light Emitting Diode):
Set the meter on "Diode Test" Mode and connect the positive probe to cathode and the negative probe to anode. If LED doesn't light up, reverse the test probes, the good and working LED will then light up or glow, a busted LED will not.
How to test Zener Diode:
As we have discussed that the Zener operates same as a common diode so the diode test mode method will be the same for Zener. Set meter to diode test range and you should expect reading one side and when you reverse the probes you will get no reading.
