بصمات
في روبوكون أسيوط
من طرف I’d like to introduce you this simple application of power electronics.
Before I start I’d like to note that most power electronics components are a high rated devices.
The circuit I am going to explain is called series diodes connection and despite of its simplicity , it’s a very important application commonly used in HVDC application and lines and many other application.
As we now diodes can be used for rectification so it’s used in HVDC but with this application special care should be paid since we are dealing with high voltages and the problem as follow:
As we know when the diode is forward biased there is a voltage drop vary between .3v to 1.5v according to the application and it can be neglected in HVDC application but the problem is obvious when it is reverse biased since there are no two identical diodes produced by fabrication which could cause a big problem as we will see
If the two diodes are not identical this will cause that at a saturation current
.001 mA at the reverse biasing (both have the same current since they are in series)one of the diodes will has a voltage of 400Vand the other will has 1000V for example which make the other diode destroy as this 1000V may be higher than the PIV(peak inverse voltage) of the diode .
And the solution is that we can use what they call a shearing resistors to control the values of the voltages applied at each diodes at a proper value(when it`s reverse biased). As follow
The circuit may not be visible so I attach this link to see it
http://books.google.com.eg/books?id=072rwRgFpcgC&pg=PA19&lpg=PA19&dq=Series-connected+diodes+with+necessary+protection.&source=bl&ots=o6HfzRRt60&sig=XgHgdVqAUqgm9NKdz8gmWxDMvSA&hl=ar&ei=xq-MTPb0KcPU4wbV3YTRCg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CA8Q6AEwAQ#v=onepage&q=Series-connected%20diodes%20with%20necessary%20protection.&f=false
It`s figure2.8
The applied voltage is V
By applying KCL
Is1+Ir1=Is2+Ir2=Is3+Ir3
And since Ir1=Vd1/R1, Ir2=Vd2/R2 , Ir3=Vd3/R3
and V=Vd1+Vd2+Vd3
and by choosing a proper value of Vd1,Vd2,Vd3 as you like (should not exceed the PIV)
Is is saturation current of the diode and it’s known by the data sheet of the diode
Solving the equations by assuming one value of the resistors you can find the values of the resistors you can use.
Capacitors are used for smoothing and it does not draw active current so it’s not mentioned.
Now you can ensure the proper protection and good performance in your system.
Before I start I’d like to note that most power electronics components are a high rated devices.
The circuit I am going to explain is called series diodes connection and despite of its simplicity , it’s a very important application commonly used in HVDC application and lines and many other application.
As we now diodes can be used for rectification so it’s used in HVDC but with this application special care should be paid since we are dealing with high voltages and the problem as follow:
As we know when the diode is forward biased there is a voltage drop vary between .3v to 1.5v according to the application and it can be neglected in HVDC application but the problem is obvious when it is reverse biased since there are no two identical diodes produced by fabrication which could cause a big problem as we will see
If the two diodes are not identical this will cause that at a saturation current
.001 mA at the reverse biasing (both have the same current since they are in series)one of the diodes will has a voltage of 400Vand the other will has 1000V for example which make the other diode destroy as this 1000V may be higher than the PIV(peak inverse voltage) of the diode .
And the solution is that we can use what they call a shearing resistors to control the values of the voltages applied at each diodes at a proper value(when it`s reverse biased). As follow
The circuit may not be visible so I attach this link to see it
http://books.google.com.eg/books?id=072rwRgFpcgC&pg=PA19&lpg=PA19&dq=Series-connected+diodes+with+necessary+protection.&source=bl&ots=o6HfzRRt60&sig=XgHgdVqAUqgm9NKdz8gmWxDMvSA&hl=ar&ei=xq-MTPb0KcPU4wbV3YTRCg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CA8Q6AEwAQ#v=onepage&q=Series-connected%20diodes%20with%20necessary%20protection.&f=false
It`s figure2.8
The applied voltage is V
By applying KCL
Is1+Ir1=Is2+Ir2=Is3+Ir3
And since Ir1=Vd1/R1, Ir2=Vd2/R2 , Ir3=Vd3/R3
and V=Vd1+Vd2+Vd3
and by choosing a proper value of Vd1,Vd2,Vd3 as you like (should not exceed the PIV)
Is is saturation current of the diode and it’s known by the data sheet of the diode
Solving the equations by assuming one value of the resistors you can find the values of the resistors you can use.
Capacitors are used for smoothing and it does not draw active current so it’s not mentioned.
Now you can ensure the proper protection and good performance in your system.
finallyI`d like to know your opinions and if there are any problems or suggestion .
with my best wishes
the collector
