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What kind of transistor turns on with 0.2 volts?

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1

$begingroup$

I need a circuit to turn on a LED with 0.2 volts.
I want to do it with a transistor as a switch.
What kind of transistor will turn on at this voltage?

transistors mosfet bjt jfet

share|improve this question

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

New contributor

seyyedali hosseini is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  Pretty much none of them. I would recommend amplifying the signal before trying to use it as a switch, perhaps with a comparator.
  $endgroup$
  – Hearth
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  Instead of asking about a transistor which needs to turn on with only 0.2 V (there aren't any but please prove me wrong!) and assume that you can do this with only one transistor (you can't but I'd like to be proven wrong again), describe what your requirements are and ask what solutions exist. A LED will not light up with 0.2 V so there must be some other voltage present. Why 0.2 V? Do research on similar setups (switching LEDs) and learn how that's done.
  $endgroup$
  – Bimpelrekkie
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  Highly related if not duplicate: electronics.stackexchange.com/questions/129183/…
  $endgroup$
  – winny
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  0.2V isn't enough to run an LED; if you have a rail that'll drive an LED then you can use a comparator.
  $endgroup$
  – TimWescott
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  What's the LED and what's the current and voltage it requires? What power supply rails do you have?
  $endgroup$
  – jonk
  4 hours ago
  

  
  
  
  

 | 
show 1 more comment

1

$begingroup$

I need a circuit to turn on a LED with 0.2 volts.
I want to do it with a transistor as a switch.
What kind of transistor will turn on at this voltage?

transistors mosfet bjt jfet

share|improve this question

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

New contributor

seyyedali hosseini is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  Pretty much none of them. I would recommend amplifying the signal before trying to use it as a switch, perhaps with a comparator.
  $endgroup$
  – Hearth
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  Instead of asking about a transistor which needs to turn on with only 0.2 V (there aren't any but please prove me wrong!) and assume that you can do this with only one transistor (you can't but I'd like to be proven wrong again), describe what your requirements are and ask what solutions exist. A LED will not light up with 0.2 V so there must be some other voltage present. Why 0.2 V? Do research on similar setups (switching LEDs) and learn how that's done.
  $endgroup$
  – Bimpelrekkie
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  Highly related if not duplicate: electronics.stackexchange.com/questions/129183/…
  $endgroup$
  – winny
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  0.2V isn't enough to run an LED; if you have a rail that'll drive an LED then you can use a comparator.
  $endgroup$
  – TimWescott
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  What's the LED and what's the current and voltage it requires? What power supply rails do you have?
  $endgroup$
  – jonk
  4 hours ago
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

I need a circuit to turn on a LED with 0.2 volts.
I want to do it with a transistor as a switch.
What kind of transistor will turn on at this voltage?

transistors mosfet bjt jfet

share|improve this question

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

New contributor

seyyedali hosseini is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

New contributor

seyyedali hosseini is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

New contributor

seyyedali hosseini is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

New contributor

seyyedali hosseini is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 8 hours ago

seyyedali hosseiniseyyedali hosseini

122

3 Answers
3

active

oldest

votes

7

$begingroup$

Whilst I'm inclined to agree with @Bimpelrekkie that this is probably an X-Y problem, for those who might actually need such a device there are some options. Most MOSFETs are sold as enhancement or depletion mode (less commonly) devices, however it's possible to tune the threshold voltage to approximately zero +/- tens of mV.

For example, the Advanced Linear Devices ALD110800A and similar devices in that series have a nominal zero gate threshold (1uA Ids). The subthreshold behavior is fairly well documented as well.

---

For your actual situation, use CrossRoads circuit with just about any single supply op-amp or single-supply comparator. LM358 or LM393 will work fine from a 5V supply.

share|improve this answer

edited 1 hour ago

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

$endgroup$

add a comment | 

5

$begingroup$

No single transistor can do what you want. Instead, you need to use multiple transistors. A simple voltage comparator will do what you want:

^{simulate this circuit – Schematic created using CircuitLab}

R2 and R3 set the reference voltage for the base of Q2. As long as the voltage at the base of Q1 is less than Vref, all of the current through R1 will flow through Q2. As soon as the input voltage rises above 0.2V, Q2 will cut off and all of the current will flow through Q1 and the LED instead.

Note that since the emitters of the transistors need to be at a negative voltage, this circuit requires a negative supply. An alternative would be to use an IC comparator — you can find single-supply units that can work with input voltages close to ground.

share|improve this answer

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  You can approach the lower rail by using PNPs 'upside down' and a single supply.
  $endgroup$
  – Russell McMahon
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @RussellMcMahon: But then there's no overhead left for the load (LED), at least, not without adding additional transistors. At that point, just get the IC comparator, which is essentially the same thing.
  $endgroup$
  – Dave Tweed♦
  3 hours ago
  
  

  
  
  
  

add a comment | 

3

$begingroup$

^{simulate this circuit – Schematic created using CircuitLab}

You could also use an Op Amp, or a Comparator. Set one input to 0.2V, when the other input exceeds that, the output will switch.

Here's one example

https://datasheets.maximintegrated.com/en/ds/MAX9107-MAX9109.pdf

share|improve this answer

edited 2 hours ago

Dave Tweed♦

123k9153267

answered 8 hours ago

CrossRoadsCrossRoads

2,11728

$endgroup$

add a comment | 

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7

$begingroup$

Whilst I'm inclined to agree with @Bimpelrekkie that this is probably an X-Y problem, for those who might actually need such a device there are some options. Most MOSFETs are sold as enhancement or depletion mode (less commonly) devices, however it's possible to tune the threshold voltage to approximately zero +/- tens of mV.

For example, the Advanced Linear Devices ALD110800A and similar devices in that series have a nominal zero gate threshold (1uA Ids). The subthreshold behavior is fairly well documented as well.

---

For your actual situation, use CrossRoads circuit with just about any single supply op-amp or single-supply comparator. LM358 or LM393 will work fine from a 5V supply.

share|improve this answer

edited 1 hour ago

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

$endgroup$

add a comment | 

7

$begingroup$

Whilst I'm inclined to agree with @Bimpelrekkie that this is probably an X-Y problem, for those who might actually need such a device there are some options. Most MOSFETs are sold as enhancement or depletion mode (less commonly) devices, however it's possible to tune the threshold voltage to approximately zero +/- tens of mV.

For example, the Advanced Linear Devices ALD110800A and similar devices in that series have a nominal zero gate threshold (1uA Ids). The subthreshold behavior is fairly well documented as well.

---

For your actual situation, use CrossRoads circuit with just about any single supply op-amp or single-supply comparator. LM358 or LM393 will work fine from a 5V supply.

share|improve this answer

edited 1 hour ago

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

$endgroup$

add a comment | 

$begingroup$

Whilst I'm inclined to agree with @Bimpelrekkie that this is probably an X-Y problem, for those who might actually need such a device there are some options. Most MOSFETs are sold as enhancement or depletion mode (less commonly) devices, however it's possible to tune the threshold voltage to approximately zero +/- tens of mV.

For example, the Advanced Linear Devices ALD110800A and similar devices in that series have a nominal zero gate threshold (1uA Ids). The subthreshold behavior is fairly well documented as well.

---

For your actual situation, use CrossRoads circuit with just about any single supply op-amp or single-supply comparator. LM358 or LM393 will work fine from a 5V supply.

share|improve this answer

edited 1 hour ago

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

$endgroup$

share|improve this answer

edited 1 hour ago

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

answered 8 hours ago

Spehro PefhanySpehro Pefhany

213k5162432

5

$begingroup$

No single transistor can do what you want. Instead, you need to use multiple transistors. A simple voltage comparator will do what you want:

^{simulate this circuit – Schematic created using CircuitLab}

R2 and R3 set the reference voltage for the base of Q2. As long as the voltage at the base of Q1 is less than Vref, all of the current through R1 will flow through Q2. As soon as the input voltage rises above 0.2V, Q2 will cut off and all of the current will flow through Q1 and the LED instead.

Note that since the emitters of the transistors need to be at a negative voltage, this circuit requires a negative supply. An alternative would be to use an IC comparator — you can find single-supply units that can work with input voltages close to ground.

share|improve this answer

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  You can approach the lower rail by using PNPs 'upside down' and a single supply.
  $endgroup$
  – Russell McMahon
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @RussellMcMahon: But then there's no overhead left for the load (LED), at least, not without adding additional transistors. At that point, just get the IC comparator, which is essentially the same thing.
  $endgroup$
  – Dave Tweed♦
  3 hours ago
  
  

  
  
  
  

add a comment | 

5

$begingroup$

No single transistor can do what you want. Instead, you need to use multiple transistors. A simple voltage comparator will do what you want:

^{simulate this circuit – Schematic created using CircuitLab}

R2 and R3 set the reference voltage for the base of Q2. As long as the voltage at the base of Q1 is less than Vref, all of the current through R1 will flow through Q2. As soon as the input voltage rises above 0.2V, Q2 will cut off and all of the current will flow through Q1 and the LED instead.

Note that since the emitters of the transistors need to be at a negative voltage, this circuit requires a negative supply. An alternative would be to use an IC comparator — you can find single-supply units that can work with input voltages close to ground.

share|improve this answer

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  You can approach the lower rail by using PNPs 'upside down' and a single supply.
  $endgroup$
  – Russell McMahon
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @RussellMcMahon: But then there's no overhead left for the load (LED), at least, not without adding additional transistors. At that point, just get the IC comparator, which is essentially the same thing.
  $endgroup$
  – Dave Tweed♦
  3 hours ago
  
  

  
  
  
  

add a comment | 

$begingroup$

No single transistor can do what you want. Instead, you need to use multiple transistors. A simple voltage comparator will do what you want:

^{simulate this circuit – Schematic created using CircuitLab}

R2 and R3 set the reference voltage for the base of Q2. As long as the voltage at the base of Q1 is less than Vref, all of the current through R1 will flow through Q2. As soon as the input voltage rises above 0.2V, Q2 will cut off and all of the current will flow through Q1 and the LED instead.

Note that since the emitters of the transistors need to be at a negative voltage, this circuit requires a negative supply. An alternative would be to use an IC comparator — you can find single-supply units that can work with input voltages close to ground.

share|improve this answer

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

$endgroup$

share|improve this answer

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

answered 8 hours ago

Dave Tweed♦Dave Tweed

123k9153267

3

$begingroup$

^{simulate this circuit – Schematic created using CircuitLab}

You could also use an Op Amp, or a Comparator. Set one input to 0.2V, when the other input exceeds that, the output will switch.

Here's one example

https://datasheets.maximintegrated.com/en/ds/MAX9107-MAX9109.pdf

share|improve this answer

edited 2 hours ago

Dave Tweed♦

123k9153267

answered 8 hours ago

CrossRoadsCrossRoads

2,11728

$endgroup$

add a comment | 

3

$begingroup$

^{simulate this circuit – Schematic created using CircuitLab}

You could also use an Op Amp, or a Comparator. Set one input to 0.2V, when the other input exceeds that, the output will switch.

Here's one example

https://datasheets.maximintegrated.com/en/ds/MAX9107-MAX9109.pdf

share|improve this answer

edited 2 hours ago

Dave Tweed♦

123k9153267

answered 8 hours ago

CrossRoadsCrossRoads

2,11728

$endgroup$

add a comment | 

$begingroup$

^{simulate this circuit – Schematic created using CircuitLab}

You could also use an Op Amp, or a Comparator. Set one input to 0.2V, when the other input exceeds that, the output will switch.

Here's one example

https://datasheets.maximintegrated.com/en/ds/MAX9107-MAX9109.pdf

share|improve this answer

edited 2 hours ago

Dave Tweed♦

123k9153267

answered 8 hours ago

CrossRoadsCrossRoads

2,11728

$endgroup$

share|improve this answer

edited 2 hours ago

Dave Tweed♦

123k9153267

answered 8 hours ago

CrossRoadsCrossRoads

2,11728

edited 2 hours ago

Dave Tweed♦

123k9153267

edited 2 hours ago

Dave Tweed♦

123k9153267

answered 8 hours ago

CrossRoadsCrossRoads

2,11728

answered 8 hours ago

CrossRoadsCrossRoads

2,11728