How to Test a Silicon Diode with a Multimeter
Check for a diode check mode., Shut off power to the circuit., Select the diode check function., Identify the positive and negative sides of the diode., Test the forward bias of the diode., Test the reverse bias.
Step-by-Step Guide
-
Step 1: Check for a diode check mode.
Most digital multimeters have a diode check mode.
To enable this mode, turn the dial to the symbol for "diode:" a black arrow pointing to a vertical line.
If your multimeter does not have this mode, test resistance instead. -
Step 2: Shut off power to the circuit.
Turn off all power to the circuit.
Test voltage across the diode to confirm there is no charge.
If the voltage reading is zero, continue to the next step.
If the power is off but there is still voltage, you may need to discharge capacitors in the circuit.This is highly dangerous and should not be attempted by novices.
If the diode is connected to other components in parallel, you may need to remove the diode from the circuit completely.
This usually requires desoldering, then soldering it back once you're done testing. , Turn the dial back to diode check mode.
Confirm that the black (negative) lead is plugged into the port marked COM, and the red (positive) lead is plugged into the port marked V, Ω, and/or R.
Touch the leads together and listen for a tone that indicates continuity.
If you do not hear anything, double check that your multimeter is on and set up correctly.
If you do hear a tone, the function is working.
Continue to the next step.
This mode produces a current in order to measure the diode's voltage, but this current is too small to damage any typical component. , The two ends of the diode have opposite polarity.
The cathode, or negative end, is usually marked with a stripe.
The anode, or positive end, is usually left unmarked.
If your diode uses a different labeling system, look up the manufacturer's guide.
Alternatively, conduct the tests and examine the results to determine which is the cathode. , A forward-biased diode has a positive charge flowing from the anode to the cathode.
Touch the red (positive) lead to the wire on the anode side, and the black (negative lead) to the wire on the cathode side.
Interpret the results:
A result between about
0.5 to
0.8 volts means the diode is working.Some multimeters will also beep to indicate continuity.
A result of OL (overload) means the diode is opened, blocking all current flow.
This diode needs to be replaced, but check the next test first.
You may have hooked up your multimeter in the wrong direction.
A result of
0.4 volts or less means the diode may be shorted.
Confirm this with the next test., A reverse-biased diode has a positive charge on the cathode side, and a more negative charge at the anode.
Diodes are designed to prevent current flowing in this direction.
To test whether this is working, just switch the position of the leads.
The red (positive) lead should be next to the striped cathode, and the black (negative) lead should be next to the anode.
Read the multimeter display:
A result of OL (overload) means the diode is successfully blocking the current.
A result of
0.5 to
0.8 volts means you've made a mistake.
You are actually testing the forward bias. (The previous test you did should have a result of OL.) If the forward-biased result was
0.4 volts or less, and this test gives the same result, the diode is shorted and needs replacement.
If the forward-biased result was
0.4 volts or less, but this test is successful (OL), you may be working with a germanium diode, not a silicon one. -
Step 3: Select the diode check function.
-
Step 4: Identify the positive and negative sides of the diode.
-
Step 5: Test the forward bias of the diode.
-
Step 6: Test the reverse bias.
Detailed Guide
Most digital multimeters have a diode check mode.
To enable this mode, turn the dial to the symbol for "diode:" a black arrow pointing to a vertical line.
If your multimeter does not have this mode, test resistance instead.
Turn off all power to the circuit.
Test voltage across the diode to confirm there is no charge.
If the voltage reading is zero, continue to the next step.
If the power is off but there is still voltage, you may need to discharge capacitors in the circuit.This is highly dangerous and should not be attempted by novices.
If the diode is connected to other components in parallel, you may need to remove the diode from the circuit completely.
This usually requires desoldering, then soldering it back once you're done testing. , Turn the dial back to diode check mode.
Confirm that the black (negative) lead is plugged into the port marked COM, and the red (positive) lead is plugged into the port marked V, Ω, and/or R.
Touch the leads together and listen for a tone that indicates continuity.
If you do not hear anything, double check that your multimeter is on and set up correctly.
If you do hear a tone, the function is working.
Continue to the next step.
This mode produces a current in order to measure the diode's voltage, but this current is too small to damage any typical component. , The two ends of the diode have opposite polarity.
The cathode, or negative end, is usually marked with a stripe.
The anode, or positive end, is usually left unmarked.
If your diode uses a different labeling system, look up the manufacturer's guide.
Alternatively, conduct the tests and examine the results to determine which is the cathode. , A forward-biased diode has a positive charge flowing from the anode to the cathode.
Touch the red (positive) lead to the wire on the anode side, and the black (negative lead) to the wire on the cathode side.
Interpret the results:
A result between about
0.5 to
0.8 volts means the diode is working.Some multimeters will also beep to indicate continuity.
A result of OL (overload) means the diode is opened, blocking all current flow.
This diode needs to be replaced, but check the next test first.
You may have hooked up your multimeter in the wrong direction.
A result of
0.4 volts or less means the diode may be shorted.
Confirm this with the next test., A reverse-biased diode has a positive charge on the cathode side, and a more negative charge at the anode.
Diodes are designed to prevent current flowing in this direction.
To test whether this is working, just switch the position of the leads.
The red (positive) lead should be next to the striped cathode, and the black (negative) lead should be next to the anode.
Read the multimeter display:
A result of OL (overload) means the diode is successfully blocking the current.
A result of
0.5 to
0.8 volts means you've made a mistake.
You are actually testing the forward bias. (The previous test you did should have a result of OL.) If the forward-biased result was
0.4 volts or less, and this test gives the same result, the diode is shorted and needs replacement.
If the forward-biased result was
0.4 volts or less, but this test is successful (OL), you may be working with a germanium diode, not a silicon one.
About the Author
Danielle Reyes
Enthusiastic about teaching creative arts techniques through clear, step-by-step guides.
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