Skip to main content
Electrical Engineering

Return to Question

edited body
Source Link
mr_highway
mr_highway
  • 69
  • 5

I want to use a pmos (SI7157DP-T1-GE3, datasheet) as switch - controlled by an optocoupler (TLP291(V4GBTP,SE, [datasheet][2]) which is controlled by a teensy 3.6 (3V3 output voltage).

[![Schematic][3]][3]

Now I'm calculating the appropriate resistors and I wonder if I'm doing it correctly. I don't care much about switching speeds but I do care a lot about longevity of the components.

According to the datasheet typical forward current is 10mA at 1.25V (25°C). I'd like to reduce current to increase longevity.

[![forward voltage/current diagram][4]][4]

It's a little bit hard to read but at around 1.17V current seems to be 2mA. So the appropriate resistance of R1 would be 1.065k -> 1.1k

[![CTR diagram][5]][5]

At 2mA the CTR seems to be around 150% = 3mA. So R2 would be 1.666k -> 1.8k. As far as I understand it, this is the minimum value and I could use 10k as well as long as I'm ok with the resulting switching speed.

Am I dointdoing it right? Are R1=1.1K and R2=10k reasonable values? Is there anything else I should take into consideration? Thank you in advance!

[2]: https://toshiba.semicon-storage.com/info/docget.jsp?did=14152&prodName=TLP291(SE [3]: https://i.sstatic.net/m0DlC.jpg [4]: https://i.sstatic.net/AMyze.gif [5]: https://i.sstatic.net/hWSXz.gif

I want to use a pmos (SI7157DP-T1-GE3, datasheet) as switch - controlled by an optocoupler (TLP291(V4GBTP,SE, [datasheet][2]) which is controlled by a teensy 3.6 (3V3 output voltage).

[![Schematic][3]][3]

Now I'm calculating the appropriate resistors and I wonder if I'm doing it correctly. I don't care much about switching speeds but I do care a lot about longevity of the components.

According to the datasheet typical forward current is 10mA at 1.25V (25°C). I'd like to reduce current to increase longevity.

[![forward voltage/current diagram][4]][4]

It's a little bit hard to read but at around 1.17V current seems to be 2mA. So the appropriate resistance of R1 would be 1.065k -> 1.1k

[![CTR diagram][5]][5]

At 2mA the CTR seems to be around 150% = 3mA. So R2 would be 1.666k -> 1.8k. As far as I understand it, this is the minimum value and I could use 10k as well as long as I'm ok with the resulting switching speed.

Am I doint it right? Are R1=1.1K and R2=10k reasonable values? Is there anything else I should take into consideration? Thank you in advance!

[2]: https://toshiba.semicon-storage.com/info/docget.jsp?did=14152&prodName=TLP291(SE [3]: https://i.sstatic.net/m0DlC.jpg [4]: https://i.sstatic.net/AMyze.gif [5]: https://i.sstatic.net/hWSXz.gif

I want to use a pmos (SI7157DP-T1-GE3, datasheet) as switch - controlled by an optocoupler (TLP291(V4GBTP,SE, [datasheet][2]) which is controlled by a teensy 3.6 (3V3 output voltage).

[![Schematic][3]][3]

Now I'm calculating the appropriate resistors and I wonder if I'm doing it correctly. I don't care much about switching speeds but I do care a lot about longevity of the components.

According to the datasheet typical forward current is 10mA at 1.25V (25°C). I'd like to reduce current to increase longevity.

[![forward voltage/current diagram][4]][4]

It's a little bit hard to read but at around 1.17V current seems to be 2mA. So the appropriate resistance of R1 would be 1.065k -> 1.1k

[![CTR diagram][5]][5]

At 2mA the CTR seems to be around 150% = 3mA. So R2 would be 1.666k -> 1.8k. As far as I understand it, this is the minimum value and I could use 10k as well as long as I'm ok with the resulting switching speed.

Am I doing it right? Are R1=1.1K and R2=10k reasonable values? Is there anything else I should take into consideration? Thank you in advance!

[2]: https://toshiba.semicon-storage.com/info/docget.jsp?did=14152&prodName=TLP291(SE [3]: https://i.sstatic.net/m0DlC.jpg [4]: https://i.sstatic.net/AMyze.gif [5]: https://i.sstatic.net/hWSXz.gif

Source Link
mr_highway
mr_highway
  • 69
  • 5

Calculating resistors for an optocoupler controlling a pmos

I want to use a pmos (SI7157DP-T1-GE3, datasheet) as switch - controlled by an optocoupler (TLP291(V4GBTP,SE, [datasheet][2]) which is controlled by a teensy 3.6 (3V3 output voltage).

[![Schematic][3]][3]

Now I'm calculating the appropriate resistors and I wonder if I'm doing it correctly. I don't care much about switching speeds but I do care a lot about longevity of the components.

According to the datasheet typical forward current is 10mA at 1.25V (25°C). I'd like to reduce current to increase longevity.

[![forward voltage/current diagram][4]][4]

It's a little bit hard to read but at around 1.17V current seems to be 2mA. So the appropriate resistance of R1 would be 1.065k -> 1.1k

[![CTR diagram][5]][5]

At 2mA the CTR seems to be around 150% = 3mA. So R2 would be 1.666k -> 1.8k. As far as I understand it, this is the minimum value and I could use 10k as well as long as I'm ok with the resulting switching speed.

Am I doint it right? Are R1=1.1K and R2=10k reasonable values? Is there anything else I should take into consideration? Thank you in advance!

[2]: https://toshiba.semicon-storage.com/info/docget.jsp?did=14152&prodName=TLP291(SE [3]: https://i.sstatic.net/m0DlC.jpg [4]: https://i.sstatic.net/AMyze.gif [5]: https://i.sstatic.net/hWSXz.gif