Elenco Projects 306-511 - Manual (Page 13)

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Project #318
OBJECTIVE: To learn the principle of an SCR.
This circuit demonstrates the principle of the SCR (Q3). The SCR can
be thought of as an electronic switch with three leads: anode, cathode,
and gate. Like a standard diode, it permits current flow in only one
direction. It will only conduct in the forward direction when triggered
by a short pulse or steady voltage applied between the gate and
cathode terminals. One set of batteries powers the lamp, the other is
used to trigger the SCR.
Turn on the slide switch (S1) and the bulb (L1) should not light. Now
press the press switch (S2); the SCR turns on and lights the bulb. To
turn off the bulb you must turn off the slide switch (S1).
SCR 2.5V Bulb
Project #319
OBJECTIVE: To activate a motor using an SCR.
SCR & Motor
Place the fan onto the motor (M1). In this circuit, the gate is connected
to the battery (B1) through the 1K
Ω resistor (R2). When the slide
switch (S1) is turned on, it triggers the gate, the SCR (Q3) conducts,
and the motor spins. The motor continues to spin until the switch is
turned off.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation. Do not lean over the motor.
To learn more about how circuits work, visit www.snapcircuits.net or page 62 to find out about our Student Guides.