Logic-level converter FET
$begingroup$
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 Jan 7 at 17:46
Peter Mortensen
1,60031422
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
$endgroup$
add a comment |
$begingroup$
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 Jan 7 at 17:46
Peter Mortensen
1,60031422
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
$endgroup$
add a comment |
$begingroup$
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 Jan 7 at 17:46
Peter Mortensen
1,60031422
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
$endgroup$
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 Jan 7 at 17:46
Peter Mortensen
1,60031422
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
edited Jan 7 at 17:46
Peter Mortensen
1,60031422
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
edited Jan 7 at 17:46
Peter Mortensen
1,60031422
edited Jan 7 at 17:46
Peter Mortensen
1,60031422
edited Jan 7 at 17:46
Peter Mortensen
1,60031422
1,60031422
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
asked Jan 7 at 14:49
Tjaart van aswegenTjaart van aswegen
8810
8810
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
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 Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
$endgroup$
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
2
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
add a comment |
$begingroup$
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 Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
$endgroup$
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
$begingroup$
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 Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
$endgroup$
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
2
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
add a comment |
$begingroup$
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 Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
$endgroup$
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
2
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
add a comment |
$begingroup$
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 Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
$endgroup$
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 Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
answered Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
answered Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
answered Jan 7 at 15:10
Peter SmithPeter Smith
13.8k11237
13.8k11237
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
2
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
add a comment |
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
2
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:19
2
2
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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.
$endgroup$
– Kevin White
Jan 7 at 15:23
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
$begingroup$
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
$endgroup$
– Tjaart van aswegen
Jan 7 at 15:27
add a comment |
$begingroup$
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 Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
$endgroup$
add a comment |
$begingroup$
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 Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
$endgroup$
add a comment |
$begingroup$
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 Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
$endgroup$
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 Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
answered Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
answered Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
answered Jan 7 at 15:17
Spehro PefhanySpehro Pefhany
206k5155411
206k5155411
add a comment |
add a comment |
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