1. Solid state switches ,solenoids

2. Solid state switches diode Transistor Thyristor Triac
Bipole transistor
MOSFET

3. Diode

4. Bipolar Transistors
Transistors are manufactured in different shapes but they have three leads (legs).  The BASE - which is the lead responsible for activating the transistor. The COLLECTOR - which is the positive lead. The EMITTER - which is the negative lead.

5. Transistor as a switch

7. Bipolar switch

8. Darlington pair

9. Transistor needs large base current to switch on.
Output from microprocessor has a small input.
A second transistor is employed to enable a high current to be switched on. Such a combination of pair of transistor is called Darlington pair.

10. MOSFET Metal oxide field effect transistor Two types Three terminals
N channel
P channel
Three terminals
Gate (G)
Drain (D)
Source (S)

11. Operation
When MOSFET is turned on current flows from source to drain .
Voltage is applied between gate-source to turn on MOSFET.
MOSFET can be turned off by removing gate voltage.
Gate has full control over the control of MOSFET.
A level shifter buffer required to raise the voltage level at which the MOSFET starts to activate.
Interfacing with µp is simpler then transistor.

13. Thyristor

14. Thyristors have three states:
Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode
Forward blocking mode — Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not yet been triggered into conduction
Forward conducting mode — The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current"

15. Triac

16. Voltage control

17. Thyristor dc control

18. Lamp dimmer

19. Thyristor dimmers switch on at an adjustable time (phase angle) after the start of each alternating current half-cycle, thereby altering the voltage waveform applied to lamps and so changing its RMS effective value.
R1 is a current limiting resistor and R2 is a potentiometer.
By adjusting R2 thyristor can be made to trigger at any point between 0 deg and 90 deg.

20. Snubber circuit
In order to prevent sudden change in source voltage, the rate voltage changes with time is dV/dt is controlled by using a snubber circuit.

21. solenoid
Solenoid is an electromagnet which can be used as an actuator.
Electrically operated actuators.
Solenoid valves are used in hydraulic and pneumatic systems.

24. Relay