Logic-level converter FET
I have been using the BSS138 level converter circuit for a while now and today it struck me I get how the voltage is stepped up by the FET or the BSS138 when you are applying say 3.3 V on the LV side.
What happens in the FET to reverse that and make it bidirectional?
digital-logic power-electronics logic-level fet
edited yesterday
Peter Mortensen
1,60031422
asked yesterday
Tjaart van aswegenTjaart van aswegen
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I have been using the BSS138 level converter circuit for a while now and today it struck me I get how the voltage is stepped up by the FET or the BSS138 when you are applying say 3.3 V on the LV side.
What happens in the FET to reverse that and make it bidirectional?
digital-logic power-electronics logic-level fet
edited yesterday
Peter Mortensen
1,60031422
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
I have been using the BSS138 level converter circuit for a while now and today it struck me I get how the voltage is stepped up by the FET or the BSS138 when you are applying say 3.3 V on the LV side.
What happens in the FET to reverse that and make it bidirectional?
digital-logic power-electronics logic-level fet
edited yesterday
Peter Mortensen
1,60031422
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I have been using the BSS138 level converter circuit for a while now and today it struck me I get how the voltage is stepped up by the FET or the BSS138 when you are applying say 3.3 V on the LV side.
What happens in the FET to reverse that and make it bidirectional?
digital-logic power-electronics logic-level fet
digital-logic power-electronics logic-level fet
edited yesterday
Peter Mortensen
1,60031422
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited yesterday
Peter Mortensen
1,60031422
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited yesterday
Peter Mortensen
1,60031422
edited yesterday
Peter Mortensen
1,60031422
edited yesterday
Peter Mortensen
1,60031422
1,60031422
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
asked yesterday
Tjaart van aswegenTjaart van aswegen
7810
7810
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Tjaart van aswegen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
2 Answers
2
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votes
When the HV side goes low, the body diode becomes forward biased, pulling down the source to a lower voltage than the gate.
Provided the gate is pulled up to a sufficiently high voltage for that new source voltage to bias the channel into conduction, the gate pullup takes over and fully enhances the channel.
answered yesterday
Peter SmithPeter Smith
13.7k11237
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
2
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
add a comment |
When you apply 3.3V on the LV side the MOSFET turns off (Vgs ~=0) and the 10K resistor R4 pulls the drain up to 5V.
The only pull-up on either side is the 10K resistors so it can have relatively slow rise time compared to a voltage translator chip.
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
When the HV side goes low, the body diode becomes forward biased, pulling down the source to a lower voltage than the gate.
Provided the gate is pulled up to a sufficiently high voltage for that new source voltage to bias the channel into conduction, the gate pullup takes over and fully enhances the channel.
answered yesterday
Peter SmithPeter Smith
13.7k11237
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
2
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
add a comment |
When the HV side goes low, the body diode becomes forward biased, pulling down the source to a lower voltage than the gate.
Provided the gate is pulled up to a sufficiently high voltage for that new source voltage to bias the channel into conduction, the gate pullup takes over and fully enhances the channel.
answered yesterday
Peter SmithPeter Smith
13.7k11237
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
2
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
add a comment |
When the HV side goes low, the body diode becomes forward biased, pulling down the source to a lower voltage than the gate.
Provided the gate is pulled up to a sufficiently high voltage for that new source voltage to bias the channel into conduction, the gate pullup takes over and fully enhances the channel.
answered yesterday
Peter SmithPeter Smith
13.7k11237
When the HV side goes low, the body diode becomes forward biased, pulling down the source to a lower voltage than the gate.
Provided the gate is pulled up to a sufficiently high voltage for that new source voltage to bias the channel into conduction, the gate pullup takes over and fully enhances the channel.
answered yesterday
Peter SmithPeter Smith
13.7k11237
answered yesterday
Peter SmithPeter Smith
13.7k11237
answered yesterday
Peter SmithPeter Smith
13.7k11237
answered yesterday
Peter SmithPeter Smith
13.7k11237
13.7k11237
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
2
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
add a comment |
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
2
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
Thanks that helps, but i feel stupid now I found the answer as soon as I posted: cdn.sparkfun.com/tutorialimages/BD-LogicLevelConverter/… that PDF has a great explanation on page 10 and 11 of what happens
– Tjaart van aswegen
yesterday
2
2
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
Interestingly I once plotted the BSS138 characteristics in the reverse direction and the threshold was lower than in the forward direction (~0.4V in my case) so the body diode never even conducted in this application.
– Kevin White
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
I came across this brain tease today at work when I looked at one of my PCB designs and realized that my Drain and Source pins was switched and that got me thinking what actually makes it work says a lot about my PCB design skills LOL
– Tjaart van aswegen
yesterday
add a comment |
When you apply 3.3V on the LV side the MOSFET turns off (Vgs ~=0) and the 10K resistor R4 pulls the drain up to 5V.
The only pull-up on either side is the 10K resistors so it can have relatively slow rise time compared to a voltage translator chip.
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
add a comment |
When you apply 3.3V on the LV side the MOSFET turns off (Vgs ~=0) and the 10K resistor R4 pulls the drain up to 5V.
The only pull-up on either side is the 10K resistors so it can have relatively slow rise time compared to a voltage translator chip.
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
add a comment |
When you apply 3.3V on the LV side the MOSFET turns off (Vgs ~=0) and the 10K resistor R4 pulls the drain up to 5V.
The only pull-up on either side is the 10K resistors so it can have relatively slow rise time compared to a voltage translator chip.
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
When you apply 3.3V on the LV side the MOSFET turns off (Vgs ~=0) and the 10K resistor R4 pulls the drain up to 5V.
The only pull-up on either side is the 10K resistors so it can have relatively slow rise time compared to a voltage translator chip.
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
answered yesterday
Spehro PefhanySpehro Pefhany
204k4150408
204k4150408
add a comment |
add a comment |
Tjaart van aswegen is a new contributor. Be nice, and check out our Code of Conduct.
Tjaart van aswegen is a new contributor. Be nice, and check out our Code of Conduct.
Tjaart van aswegen is a new contributor. Be nice, and check out our Code of Conduct.
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