How can I change step-down my variable input voltage?
$begingroup$
Ok so here's the deal:
I have a variable DC Voltage source from 0-10V.
I need to step that down to a variable source of 0-3V.
This 0-3V DC will be fed to an Analog to Digital converter in a microcontroller.
I know I can potentially use a Voltage Divider (using resistors) but apparently, that's not a good solution.
Op-amps don't provide a gain < 1.
So I'm just struggling as to how I can accomplish this.
The microcontroller: https://www.microchip.com/wwwproducts/en/PIC18F47K42
microcontroller voltage power dc variable
edited 15 hours ago
pipe
10.2k42657
asked yesterday
Alee321Alee321
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
Ok so here's the deal:
I have a variable DC Voltage source from 0-10V.
I need to step that down to a variable source of 0-3V.
This 0-3V DC will be fed to an Analog to Digital converter in a microcontroller.
I know I can potentially use a Voltage Divider (using resistors) but apparently, that's not a good solution.
Op-amps don't provide a gain < 1.
So I'm just struggling as to how I can accomplish this.
The microcontroller: https://www.microchip.com/wwwproducts/en/PIC18F47K42
microcontroller voltage power dc variable
edited 15 hours ago
pipe
10.2k42657
asked yesterday
Alee321Alee321
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
How can you use a voltage of 0 to 3V as the supply voltage for a microcontroller? Your description of this doesn't make any sense. You should draw a schematic.
$endgroup$
– Elliot Alderson
yesterday
$begingroup$
@ElliotAlderson you're right I'm sorry. It's not to power the microcontroller. The application is to simulate dimming, based on the 0-10V from the DC Source the voltage must be stepped down from 0-3V. This is the voltage range readable by the uC which will determine the duty cycle of a PWM used to dim an LED.
$endgroup$
– Alee321
yesterday
2
$begingroup$
A resistive divider is fine then. You might want to put an op-amp voltage follower in between the divider and ADC input to buffer things but it's not always necessary. Search this site. There are many existing answers addressing your question.
$endgroup$
– Toor
yesterday
3
$begingroup$
A voltage divider may be a perfectly good solution provided (a) the source impedance isn't too high and (b) you can tolerate the small energy consumption. Your question doesn't include details of either.
$endgroup$
– Transistor
yesterday
add a comment |
$begingroup$
Ok so here's the deal:
I have a variable DC Voltage source from 0-10V.
I need to step that down to a variable source of 0-3V.
This 0-3V DC will be fed to an Analog to Digital converter in a microcontroller.
I know I can potentially use a Voltage Divider (using resistors) but apparently, that's not a good solution.
Op-amps don't provide a gain < 1.
So I'm just struggling as to how I can accomplish this.
The microcontroller: https://www.microchip.com/wwwproducts/en/PIC18F47K42
microcontroller voltage power dc variable
edited 15 hours ago
pipe
10.2k42657
asked yesterday
Alee321Alee321
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
Ok so here's the deal:
I have a variable DC Voltage source from 0-10V.
I need to step that down to a variable source of 0-3V.
This 0-3V DC will be fed to an Analog to Digital converter in a microcontroller.
I know I can potentially use a Voltage Divider (using resistors) but apparently, that's not a good solution.
Op-amps don't provide a gain < 1.
So I'm just struggling as to how I can accomplish this.
The microcontroller: https://www.microchip.com/wwwproducts/en/PIC18F47K42
microcontroller voltage power dc variable
microcontroller voltage power dc variable
edited 15 hours ago
pipe
10.2k42657
asked yesterday
Alee321Alee321
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 15 hours ago
pipe
10.2k42657
asked yesterday
Alee321Alee321
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 15 hours ago
pipe
10.2k42657
edited 15 hours ago
pipe
10.2k42657
edited 15 hours ago
pipe
10.2k42657
10.2k42657
asked yesterday
Alee321Alee321
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
Alee321Alee321
112
asked yesterday
Alee321Alee321
112
112
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Alee321 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$begingroup$
How can you use a voltage of 0 to 3V as the supply voltage for a microcontroller? Your description of this doesn't make any sense. You should draw a schematic.
$endgroup$
– Elliot Alderson
yesterday
$begingroup$
@ElliotAlderson you're right I'm sorry. It's not to power the microcontroller. The application is to simulate dimming, based on the 0-10V from the DC Source the voltage must be stepped down from 0-3V. This is the voltage range readable by the uC which will determine the duty cycle of a PWM used to dim an LED.
$endgroup$
– Alee321
yesterday
2
$begingroup$
A resistive divider is fine then. You might want to put an op-amp voltage follower in between the divider and ADC input to buffer things but it's not always necessary. Search this site. There are many existing answers addressing your question.
$endgroup$
– Toor
yesterday
3
$begingroup$
A voltage divider may be a perfectly good solution provided (a) the source impedance isn't too high and (b) you can tolerate the small energy consumption. Your question doesn't include details of either.
$endgroup$
– Transistor
yesterday
add a comment |
$begingroup$
How can you use a voltage of 0 to 3V as the supply voltage for a microcontroller? Your description of this doesn't make any sense. You should draw a schematic.
$endgroup$
– Elliot Alderson
yesterday
$begingroup$
@ElliotAlderson you're right I'm sorry. It's not to power the microcontroller. The application is to simulate dimming, based on the 0-10V from the DC Source the voltage must be stepped down from 0-3V. This is the voltage range readable by the uC which will determine the duty cycle of a PWM used to dim an LED.
$endgroup$
– Alee321
yesterday
2
$begingroup$
A resistive divider is fine then. You might want to put an op-amp voltage follower in between the divider and ADC input to buffer things but it's not always necessary. Search this site. There are many existing answers addressing your question.
$endgroup$
– Toor
yesterday
3
$begingroup$
A voltage divider may be a perfectly good solution provided (a) the source impedance isn't too high and (b) you can tolerate the small energy consumption. Your question doesn't include details of either.
$endgroup$
– Transistor
yesterday
$begingroup$
How can you use a voltage of 0 to 3V as the supply voltage for a microcontroller? Your description of this doesn't make any sense. You should draw a schematic.
$endgroup$
– Elliot Alderson
yesterday
$begingroup$
How can you use a voltage of 0 to 3V as the supply voltage for a microcontroller? Your description of this doesn't make any sense. You should draw a schematic.
$endgroup$
– Elliot Alderson
yesterday
$begingroup$
@ElliotAlderson you're right I'm sorry. It's not to power the microcontroller. The application is to simulate dimming, based on the 0-10V from the DC Source the voltage must be stepped down from 0-3V. This is the voltage range readable by the uC which will determine the duty cycle of a PWM used to dim an LED.
$endgroup$
– Alee321
yesterday
$begingroup$
@ElliotAlderson you're right I'm sorry. It's not to power the microcontroller. The application is to simulate dimming, based on the 0-10V from the DC Source the voltage must be stepped down from 0-3V. This is the voltage range readable by the uC which will determine the duty cycle of a PWM used to dim an LED.
$endgroup$
– Alee321
yesterday
2
2
$begingroup$
A resistive divider is fine then. You might want to put an op-amp voltage follower in between the divider and ADC input to buffer things but it's not always necessary. Search this site. There are many existing answers addressing your question.
$endgroup$
– Toor
yesterday
$begingroup$
A resistive divider is fine then. You might want to put an op-amp voltage follower in between the divider and ADC input to buffer things but it's not always necessary. Search this site. There are many existing answers addressing your question.
$endgroup$
– Toor
yesterday
3
3
$begingroup$
A voltage divider may be a perfectly good solution provided (a) the source impedance isn't too high and (b) you can tolerate the small energy consumption. Your question doesn't include details of either.
$endgroup$
– Transistor
yesterday
$begingroup$
A voltage divider may be a perfectly good solution provided (a) the source impedance isn't too high and (b) you can tolerate the small energy consumption. Your question doesn't include details of either.
$endgroup$
– Transistor
yesterday
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
R divider works fine as long as R is not too high.
If you know the conversion rate and Hold Cap acquisition time
EQUATION 36-1: ACQUISITION TIME EXAMPLE in the datasheet provides the formula and example of choosing R values < 10k.
Rs is the source equivalent // resistance of the R divider, R1//R2.
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
$endgroup$
add a comment |
$begingroup$
A resistor divider works fine as long as the source impedance is low and the ADC impedance is high (compared to the resistors used for the divider).
If your source impedance is high, use an opamp in voltage follower mode (gain = 1) before the divider. If your ADC impedance is low (unlikely) use a voltage follower after the divider.
answered yesterday
evildemonicevildemonic
2,377721
$endgroup$
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
add a comment |
$begingroup$
In addition to @Toor suggestion (voltage follower and voltage divider) and in response to OP statement
Op-amps don't provide a gain < 1.
follows my alternative configuration using a single supply difference amplifier. The output is reversed - if you do not mind correct it in software applying $V_o=3 - 0.3V_i$.
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
$endgroup$
1
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
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votes
active
oldest
votes
$begingroup$
R divider works fine as long as R is not too high.
If you know the conversion rate and Hold Cap acquisition time
EQUATION 36-1: ACQUISITION TIME EXAMPLE in the datasheet provides the formula and example of choosing R values < 10k.
Rs is the source equivalent // resistance of the R divider, R1//R2.
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
$endgroup$
add a comment |
$begingroup$
R divider works fine as long as R is not too high.
If you know the conversion rate and Hold Cap acquisition time
EQUATION 36-1: ACQUISITION TIME EXAMPLE in the datasheet provides the formula and example of choosing R values < 10k.
Rs is the source equivalent // resistance of the R divider, R1//R2.
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
$endgroup$
add a comment |
$begingroup$
R divider works fine as long as R is not too high.
If you know the conversion rate and Hold Cap acquisition time
EQUATION 36-1: ACQUISITION TIME EXAMPLE in the datasheet provides the formula and example of choosing R values < 10k.
Rs is the source equivalent // resistance of the R divider, R1//R2.
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
$endgroup$
R divider works fine as long as R is not too high.
If you know the conversion rate and Hold Cap acquisition time
EQUATION 36-1: ACQUISITION TIME EXAMPLE in the datasheet provides the formula and example of choosing R values < 10k.
Rs is the source equivalent // resistance of the R divider, R1//R2.
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
answered yesterday
Sunnyskyguy EE75Sunnyskyguy EE75
68.8k22598
68.8k22598
add a comment |
add a comment |
$begingroup$
A resistor divider works fine as long as the source impedance is low and the ADC impedance is high (compared to the resistors used for the divider).
If your source impedance is high, use an opamp in voltage follower mode (gain = 1) before the divider. If your ADC impedance is low (unlikely) use a voltage follower after the divider.
answered yesterday
evildemonicevildemonic
2,377721
$endgroup$
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
add a comment |
$begingroup$
A resistor divider works fine as long as the source impedance is low and the ADC impedance is high (compared to the resistors used for the divider).
If your source impedance is high, use an opamp in voltage follower mode (gain = 1) before the divider. If your ADC impedance is low (unlikely) use a voltage follower after the divider.
answered yesterday
evildemonicevildemonic
2,377721
$endgroup$
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
add a comment |
$begingroup$
A resistor divider works fine as long as the source impedance is low and the ADC impedance is high (compared to the resistors used for the divider).
If your source impedance is high, use an opamp in voltage follower mode (gain = 1) before the divider. If your ADC impedance is low (unlikely) use a voltage follower after the divider.
answered yesterday
evildemonicevildemonic
2,377721
$endgroup$
A resistor divider works fine as long as the source impedance is low and the ADC impedance is high (compared to the resistors used for the divider).
If your source impedance is high, use an opamp in voltage follower mode (gain = 1) before the divider. If your ADC impedance is low (unlikely) use a voltage follower after the divider.
answered yesterday
evildemonicevildemonic
2,377721
answered yesterday
evildemonicevildemonic
2,377721
answered yesterday
evildemonicevildemonic
2,377721
answered yesterday
evildemonicevildemonic
2,377721
2,377721
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
add a comment |
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
$begingroup$
ADCs can have low input impedances, because those sample-and-hold circuits have a capacitor that needs to be charged! A tiny one, but it's still there. Too high a resistance can mean you need to sample for longer, slowing your reads, which may or may not be acceptable.
$endgroup$
– Hearth
yesterday
add a comment |
$begingroup$
In addition to @Toor suggestion (voltage follower and voltage divider) and in response to OP statement
Op-amps don't provide a gain < 1.
follows my alternative configuration using a single supply difference amplifier. The output is reversed - if you do not mind correct it in software applying $V_o=3 - 0.3V_i$.
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
$endgroup$
1
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
add a comment |
$begingroup$
In addition to @Toor suggestion (voltage follower and voltage divider) and in response to OP statement
Op-amps don't provide a gain < 1.
follows my alternative configuration using a single supply difference amplifier. The output is reversed - if you do not mind correct it in software applying $V_o=3 - 0.3V_i$.
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
$endgroup$
1
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
add a comment |
$begingroup$
In addition to @Toor suggestion (voltage follower and voltage divider) and in response to OP statement
Op-amps don't provide a gain < 1.
follows my alternative configuration using a single supply difference amplifier. The output is reversed - if you do not mind correct it in software applying $V_o=3 - 0.3V_i$.
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
$endgroup$
In addition to @Toor suggestion (voltage follower and voltage divider) and in response to OP statement
Op-amps don't provide a gain < 1.
follows my alternative configuration using a single supply difference amplifier. The output is reversed - if you do not mind correct it in software applying $V_o=3 - 0.3V_i$.
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
answered yesterday
Dirceu Rodrigues JrDirceu Rodrigues Jr
1,838612
1,838612
1
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
add a comment |
1
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
1
1
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
As opposed to my voltage follower suggestion, this one has better common-mode rejection at the expense of inverting the signal.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
Are those resistor values correct? I think it's supposed to be more along the lines of 6.66K/3.33K, or 10K/5K or something like that.
$endgroup$
– Toor
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
$begingroup$
I think that it's correct. Try to apply superposition to inputs 10 V and Vi.
$endgroup$
– Dirceu Rodrigues Jr
yesterday
add a comment |
Alee321 is a new contributor. Be nice, and check out our Code of Conduct.
Alee321 is a new contributor. Be nice, and check out our Code of Conduct.
Alee321 is a new contributor. Be nice, and check out our Code of Conduct.
Alee321 is a new contributor. Be nice, and check out our Code of Conduct.
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How can you use a voltage of 0 to 3V as the supply voltage for a microcontroller? Your description of this doesn't make any sense. You should draw a schematic.
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– Elliot Alderson
yesterday
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@ElliotAlderson you're right I'm sorry. It's not to power the microcontroller. The application is to simulate dimming, based on the 0-10V from the DC Source the voltage must be stepped down from 0-3V. This is the voltage range readable by the uC which will determine the duty cycle of a PWM used to dim an LED.
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– Alee321
yesterday
2
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A resistive divider is fine then. You might want to put an op-amp voltage follower in between the divider and ADC input to buffer things but it's not always necessary. Search this site. There are many existing answers addressing your question.
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– Toor
yesterday
3
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A voltage divider may be a perfectly good solution provided (a) the source impedance isn't too high and (b) you can tolerate the small energy consumption. Your question doesn't include details of either.
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– Transistor
yesterday