Could anyone help me to understand the following circuit?
up vote
3
down vote
favorite
I used the following circuit to control the outdoor light, and it works as I wanted.
I am trying to understand the circuit and it looks like a comparator circuit,
but I don't understand the use of 100 kOhm feedback resistor.
Also how to choose the resistor values 100 kOhm, 15 kOhm and 100 kOhm pot?
Can anyone help me?
Regards
ldr
edited 2 hours ago
Michel Keijzers
5,59082461
asked 2 hours ago
vtc
164
add a comment |
up vote
3
down vote
favorite
I used the following circuit to control the outdoor light, and it works as I wanted.
I am trying to understand the circuit and it looks like a comparator circuit,
but I don't understand the use of 100 kOhm feedback resistor.
Also how to choose the resistor values 100 kOhm, 15 kOhm and 100 kOhm pot?
Can anyone help me?
Regards
ldr
edited 2 hours ago
Michel Keijzers
5,59082461
asked 2 hours ago
vtc
164
The resistors picked depend on the LDR used and what you want to achive. About the feedback resistor : the comparator has Hysteresis so at the treshold point the RL1 doesn't switch on and off for multiple times.
– pantarhei
2 hours ago
add a comment |
up vote
3
down vote
favorite
up vote
3
down vote
favorite
I used the following circuit to control the outdoor light, and it works as I wanted.
I am trying to understand the circuit and it looks like a comparator circuit,
but I don't understand the use of 100 kOhm feedback resistor.
Also how to choose the resistor values 100 kOhm, 15 kOhm and 100 kOhm pot?
Can anyone help me?
Regards
ldr
edited 2 hours ago
Michel Keijzers
5,59082461
asked 2 hours ago
vtc
164
I used the following circuit to control the outdoor light, and it works as I wanted.
I am trying to understand the circuit and it looks like a comparator circuit,
but I don't understand the use of 100 kOhm feedback resistor.
Also how to choose the resistor values 100 kOhm, 15 kOhm and 100 kOhm pot?
Can anyone help me?
Regards
ldr
ldr
edited 2 hours ago
Michel Keijzers
5,59082461
asked 2 hours ago
vtc
164
edited 2 hours ago
Michel Keijzers
5,59082461
asked 2 hours ago
vtc
164
edited 2 hours ago
Michel Keijzers
5,59082461
edited 2 hours ago
Michel Keijzers
5,59082461
edited 2 hours ago
Michel Keijzers
5,59082461
5,59082461
asked 2 hours ago
vtc
164
asked 2 hours ago
vtc
164
asked 2 hours ago
vtc
164
164
The resistors picked depend on the LDR used and what you want to achive. About the feedback resistor : the comparator has Hysteresis so at the treshold point the RL1 doesn't switch on and off for multiple times.
– pantarhei
2 hours ago
add a comment |
The resistors picked depend on the LDR used and what you want to achive. About the feedback resistor : the comparator has Hysteresis so at the treshold point the RL1 doesn't switch on and off for multiple times.
– pantarhei
2 hours ago
The resistors picked depend on the LDR used and what you want to achive. About the feedback resistor : the comparator has Hysteresis so at the treshold point the RL1 doesn't switch on and off for multiple times.
– pantarhei
2 hours ago
The resistors picked depend on the LDR used and what you want to achive. About the feedback resistor : the comparator has Hysteresis so at the treshold point the RL1 doesn't switch on and off for multiple times.
– pantarhei
2 hours ago
add a comment |
1 Answer
1
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oldest
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up vote
5
down vote
The point of the 100k feedback resistor is to provide hysteresis. Without it, if the LDR was very close to the threshold, it could switch on and off rapidly. Adding the feedback resistor will change the voltage level of the non-inverting input when the comparator is activated. This will mean that the LDR will have a bit of headroom to once again reach the threshold voltage.
This picture shows how the hysteresis helps. You can see that once the non-inverting input has reached the lower threshold, the OUT changes LOW. Only when it reaches the upper threshold will it go back high again.
Without hysteresis, you could end up with an unstable output, especially if the light level is very close to the threshold
Some further reading on this can be found in a nice application note by Maxim Integrated: Application note 3616
This application note goes through the math required to select values for your resistors. The only one it cannot select is your LDR. You can, however, calculate a fixed resistor, then choose a suitable LDR from that.
answered 2 hours ago
MCG
5,75031445
add a comment |
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1 Answer
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active
oldest
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1 Answer
1
active
oldest
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active
oldest
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active
oldest
votes
up vote
5
down vote
The point of the 100k feedback resistor is to provide hysteresis. Without it, if the LDR was very close to the threshold, it could switch on and off rapidly. Adding the feedback resistor will change the voltage level of the non-inverting input when the comparator is activated. This will mean that the LDR will have a bit of headroom to once again reach the threshold voltage.
This picture shows how the hysteresis helps. You can see that once the non-inverting input has reached the lower threshold, the OUT changes LOW. Only when it reaches the upper threshold will it go back high again.
Without hysteresis, you could end up with an unstable output, especially if the light level is very close to the threshold
Some further reading on this can be found in a nice application note by Maxim Integrated: Application note 3616
This application note goes through the math required to select values for your resistors. The only one it cannot select is your LDR. You can, however, calculate a fixed resistor, then choose a suitable LDR from that.
answered 2 hours ago
MCG
5,75031445
add a comment |
up vote
5
down vote
The point of the 100k feedback resistor is to provide hysteresis. Without it, if the LDR was very close to the threshold, it could switch on and off rapidly. Adding the feedback resistor will change the voltage level of the non-inverting input when the comparator is activated. This will mean that the LDR will have a bit of headroom to once again reach the threshold voltage.
This picture shows how the hysteresis helps. You can see that once the non-inverting input has reached the lower threshold, the OUT changes LOW. Only when it reaches the upper threshold will it go back high again.
Without hysteresis, you could end up with an unstable output, especially if the light level is very close to the threshold
Some further reading on this can be found in a nice application note by Maxim Integrated: Application note 3616
This application note goes through the math required to select values for your resistors. The only one it cannot select is your LDR. You can, however, calculate a fixed resistor, then choose a suitable LDR from that.
answered 2 hours ago
MCG
5,75031445
add a comment |
up vote
5
down vote
up vote
5
down vote
The point of the 100k feedback resistor is to provide hysteresis. Without it, if the LDR was very close to the threshold, it could switch on and off rapidly. Adding the feedback resistor will change the voltage level of the non-inverting input when the comparator is activated. This will mean that the LDR will have a bit of headroom to once again reach the threshold voltage.
This picture shows how the hysteresis helps. You can see that once the non-inverting input has reached the lower threshold, the OUT changes LOW. Only when it reaches the upper threshold will it go back high again.
Without hysteresis, you could end up with an unstable output, especially if the light level is very close to the threshold
Some further reading on this can be found in a nice application note by Maxim Integrated: Application note 3616
This application note goes through the math required to select values for your resistors. The only one it cannot select is your LDR. You can, however, calculate a fixed resistor, then choose a suitable LDR from that.
answered 2 hours ago
MCG
5,75031445
The point of the 100k feedback resistor is to provide hysteresis. Without it, if the LDR was very close to the threshold, it could switch on and off rapidly. Adding the feedback resistor will change the voltage level of the non-inverting input when the comparator is activated. This will mean that the LDR will have a bit of headroom to once again reach the threshold voltage.
This picture shows how the hysteresis helps. You can see that once the non-inverting input has reached the lower threshold, the OUT changes LOW. Only when it reaches the upper threshold will it go back high again.
Without hysteresis, you could end up with an unstable output, especially if the light level is very close to the threshold
Some further reading on this can be found in a nice application note by Maxim Integrated: Application note 3616
This application note goes through the math required to select values for your resistors. The only one it cannot select is your LDR. You can, however, calculate a fixed resistor, then choose a suitable LDR from that.
answered 2 hours ago
MCG
5,75031445
edited 2 hours ago
answered 2 hours ago
MCG
5,75031445
answered 2 hours ago
MCG
5,75031445
answered 2 hours ago
MCG
5,75031445
5,75031445
add a comment |
add a comment |
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The resistors picked depend on the LDR used and what you want to achive. About the feedback resistor : the comparator has Hysteresis so at the treshold point the RL1 doesn't switch on and off for multiple times.
– pantarhei
2 hours ago