SCR Testing | SCR Test and Measurement
This article on SCR testing covers various test and measurement parameters used to evaluate SCR. It mentions test setup used for various measurements during SCR testing.
What is SCR?
• SCR stands for Silicon Controlled Rectifier.
• It is 3 terminal 4 later (P-N-P-N) semiconductor device. It is made using N-P semiconductor. Anode is near P type (towards left) and cathode is near N type (towards right) semiconductor terminal.
• As it conducts current only in one direction, it can be used as switch.
• The figure-1 depicts SCR appearance and symbol.
• It is also known as thyristor.
• It has many applications in electronics. It is mainly used for power control. One SCR can control half of the AC cycle.
Following are the applications of SCR (i.e. thyristor).
• AC power control in lights, motors etc.
• Over voltage protection for power supplies.
• AC power switching
• As control elements in phase angle triggered controllers.
• Used in photographic flash lights
Following specifications of SCR (Thyristor) are verified during
• Maximum rise of ON-state current (dI/dt)
• Peak Gate Current (IGM)
• Gate trigger current (IGT)
• Over current protection (I2)*t)
• Average ON-state current (IT(AV))
SCR testing youtube video
Check youtube video to understand SCR operation, SCR pin designations and SCR working or healthy condition.
Test Setup for SCR Testing
Multimeter is used for SCR testing. SCRs are just like diodes but they can handle much more current than diodes. Moreover they need to be turned ON unlike typical conventional diodes. During this test, we will see whether SCR is in working condition or not. Check the datasheet of the SCR as per part number to determine pin designations.
➤Keep the multimeter in diode test mode. Just connecting Anode and Cathode to positive and negative terminals of
the multimeter do not provide any readings until SCR is not turned ON.
➤SCR is turned ON by applying positive voltage to the Gate terminal.
➤Now connecting positive and negative cables of multimeter to Anode and Cathode will provide reading of about 0.7 Volt. This is forward voltage of the SCR.
➤Similarly load (i.e. small lamp) can be interfaced with the SCR and checked when gate is given positive voltage.