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SCRs And Triacs
SCRs and triacs are semiconductor components that are used in switching applications. A SCR
(silicon controlled rectifier) is used for DC switching circuits. A triac is used for AC switching
circuits. This section will demonstrate how to dynamically test these components.
Silicon Controlled Rectifiers (SCR’s)
The SCR is a switching semiconductor device that conducts positive current only. Its symbol and
equivalent circuit can be seen below. When the gate (G) is at the same voltage level as the
cathode (K), the SCR acts as an open. When the gate is forced more positive than the cathode,
positive current flows between the anode (A) and the cathode.
Figure 6-36. Diagram of a Silicon Controlled Rectifier
1. Select the 15V, 10 kΩ
ΩΩ
Ω range.
2. Place or clip the red test probe from the Tracker 2700's A test terminal to gate lead (G) of the
component.
3. Place or clip the black test probe from the Tracker 2700's Common terminal to anode lead (A)
of the component.
4. Observe the gate-anode signature of the SCR.
5. Move the black test probe from the SCR's anode lead to cathode lead (K) of the component.
6. Observe the anode-cathode signature.
7. Observe the gate-cathode signature of the SCR.
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