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A Level     >Power Switching<     Capacitor Phase     Diac     MOSFET     Phase     Relay     Thyristor     Thyristor AC     Transistor     Triac    

Power Switching


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Switching Device Options

Device

Advantages

Disadvantages

Cost

Switch (hand operated) Simple and cheap. No automation is possible. £1
Electromagnetic Relay High voltages and currents can be switched.
AC can be switched.
Minimal energy lost in the switch.
No waste heat.
Slow.
Moving parts make it unreliable.
The coil current has to be present to keep the device on.
Quite expensive.
£3

Bipolar Transistor

BC182L Datasheet

Fast.
No moving parts.
Reliable.
Low cost in low power scenarios.
Saturation RCE is about 10 Ohm (ballpark figure)
Low power switching only.
High voltages are not possible.
AC switching can't be achieved with a single device.
There is significant waste heat in the device.
The base current has to be present to keep the device on.
Saturation    Vce = 0.25 to 0.6V
0.1p

MOSFET

IRF640 Dtatsheet

Faster than bipolar.
No moving parts.
Voltages up to about 100 V are possible.
Less waste heat than bipolar devices.
Better for high power switching.
Saturation RDS is about 1 Ohm
AC switching can't be achieved with a single device.
There is significant waste heat in the device.
The gate voltage has to be present to keep the device on.
£1

Thyristor

BTW69-1200N Data Sheet

Very simple circuitry.
A single short pulse turns on the device.
A second short pulse can turn it off again.
These devices can switch high voltages up to 1200 V and 50 Amps.
Very fast switching.
Low cost.
Waste heat less problematic.
Dynamic ( on ) resistance 8.5 milliOhm!

DC only. 
 
40p

Triac

MAC15 Series Datasheet

DC and AC.
This is effectively two thyristors back to back.
The properties are bi-directional.
Waste heat less problematic.
Low cost.
  30p
Diac It's turned on by voltages above its break-over voltage.
This can be used to "crowbar" power supply over-voltage surges.
If the voltage becomes too great, the fuse gets blown.
Its speed and performance are similar to Thyristors and Triacs.
On its own it's not suitable for control system switching. 20p

 

 

 

 

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