Hi folks.
Here we are going to talk about one of the 3 pillars of electrical engineering – Power electronics (other two being electrical machines and power systems).
Semiconductor switches play a very vital role in any power electronic circuit. Let us talk about them first.
There are switches we use in home (the mechanical ones) that we operate conveniently with hands. We can’t use them in electrical circuits where we need high precision and speed of operation (this where relays fail). Functionality would be same if you compare.
What do we exactly want from a switch?
It should have high break down voltage (voltage it can sustain without damaging when reverse biased).
It should have low conduction loss (ON state voltage drop across it should be minimum).
It should have fast transition from On to Off and vice versa to achieve higher switching frequency.
We have some switches that use lightly doped semiconductor on either side of the PN junction to achieve high break down strength (lesser the impurity, more the force needed to throw them across barrier). But lightly doped materials have higher resistance and higher ON state voltage drop (lesser number of charges available to flow). Let us call these devices as GROUP 1(G1).
So overcome this issue we (the electrical engineers) invented a phenomenon called conductivity modulation. (Understand it as some process and for those who have got extra interest- it a phenomenon where p and n- junction is there and hole injection takes place in n- causing voltage peak in turn on characteristics). So due to this process turn loss reduces. Turn of process is carried out by injecting charges and Turn off process is carried out by removal of charge. But this takes time and reduces the speed of operation. Let us call them GROUP 2 (G2).
G1 have no conductivity modulation and hence they can operate at higher switching frequency than G2.
G1 have very high losses if operated for high power applications and hence most commonly used for low power applications. G2 have low power loss and hence used for high power applications.
G1 are majority carrier device and G2 are minority carrier devices (due to conductivity modulation).
G1 devices = MOSFET
G2 devices = POWER DIODE, SCR, GTO (Notice the presence of p and n- junction as well as voltage peak in turn ON characteristics of these devices).
Comparing, MOSFETs are used for high frequency (in MHz) and low power applications. They have high ON state loss and are majority carrier devices. SCRs are used for high power (current rating in KA) and low frequency (less than 250 Hz). They have low ON state loss and are minority carrier devices.
Thank you for your time and please feel free to leave comments about your views. You can mail your doubts at dnachiketa1010@gmail.com
Here we are going to talk about one of the 3 pillars of electrical engineering – Power electronics (other two being electrical machines and power systems).
Semiconductor switches play a very vital role in any power electronic circuit. Let us talk about them first.
There are switches we use in home (the mechanical ones) that we operate conveniently with hands. We can’t use them in electrical circuits where we need high precision and speed of operation (this where relays fail). Functionality would be same if you compare.
What do we exactly want from a switch?
It should have high break down voltage (voltage it can sustain without damaging when reverse biased).
It should have low conduction loss (ON state voltage drop across it should be minimum).
It should have fast transition from On to Off and vice versa to achieve higher switching frequency.
We have some switches that use lightly doped semiconductor on either side of the PN junction to achieve high break down strength (lesser the impurity, more the force needed to throw them across barrier). But lightly doped materials have higher resistance and higher ON state voltage drop (lesser number of charges available to flow). Let us call these devices as GROUP 1(G1).
So overcome this issue we (the electrical engineers) invented a phenomenon called conductivity modulation. (Understand it as some process and for those who have got extra interest- it a phenomenon where p and n- junction is there and hole injection takes place in n- causing voltage peak in turn on characteristics). So due to this process turn loss reduces. Turn of process is carried out by injecting charges and Turn off process is carried out by removal of charge. But this takes time and reduces the speed of operation. Let us call them GROUP 2 (G2).
G1 have no conductivity modulation and hence they can operate at higher switching frequency than G2.
G1 have very high losses if operated for high power applications and hence most commonly used for low power applications. G2 have low power loss and hence used for high power applications.
G1 are majority carrier device and G2 are minority carrier devices (due to conductivity modulation).
G1 devices = MOSFET
G2 devices = POWER DIODE, SCR, GTO (Notice the presence of p and n- junction as well as voltage peak in turn ON characteristics of these devices).
Comparing, MOSFETs are used for high frequency (in MHz) and low power applications. They have high ON state loss and are majority carrier devices. SCRs are used for high power (current rating in KA) and low frequency (less than 250 Hz). They have low ON state loss and are minority carrier devices.
Thank you for your time and please feel free to leave comments about your views. You can mail your doubts at dnachiketa1010@gmail.com
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