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Constant Current with PWM

ronsimpson

Well-Known Member
Most Helpful Member
As you have been told before:
-NE555 is not a PWM. You can trick it into working.
-The 1A must come from the 15V supply. So much of the 1A must pass through the 178400 regulator. 1A x 10V = 10 watts. (hot and dead)
A NE555 running at 5 volts can not pull up enough to turn on the 2N7000. This is a Source Follower not a Switch.
-5V1 diode has no function.
-2N7000 is only good for 200mA.
 
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schmitt trigger

Well-Known Member
That schematic has so many errors that I cannot see what you are attempting to do.

l will only focus on the LM311, which has significant differences to the more common LM339.
For starters , it has an emitter output which is not shown, and requires to be connected to something otherwise you don’t have an output.
There are a pair of strobe/balance pins which can pick up noise if not terminated. And you cannot show how to terminate them if they are not drawn.
The output is an open collector and as such it requires a pull-up resistor which is not included.
The LM311 is a comparator, not an opamp. As such it requires positive feedback, not negative feedback as shown.
 
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s3rg3n123

New Member
That schematic has so many errors that I cannot see what you are attempting to do.

l will only focus on the LM311, which has significant differences to the more common LM339.
For starters , it has an emitter output which is not shown, and requires to be connected to something otherwise you don’t have an output.
There are a pair of strobe/balance pins which can pick up noise if not terminated. And you cannot show how to terminate them if they are not drawn.
Information on how the circuit works is available on this site. https://www.instructables.com/id/Electronics-Projects-Constant-Current-Power-Suppl/

But,i couldn't understand how the output current value set up here
 

ronsimpson

Well-Known Member
Most Helpful Member
Output current: 2mA
At the link, the LED current is 0.002A not 1A.
The circuit is full of problems.
Don't believe every thing you see on the internet. About 1/2 the circuits on the internet have serious errors. This one has many errors.
Going to a different forum will not change the answer.
 

s3rg3n123

New Member
At the link, the LED current is 0.002A not 1A.
The circuit is full of problems.
Don't believe every thing you see on the internet. About 1/2 the circuits on the internet have serious errors. This one has many errors.
Going to a different forum will not change the answer.
My goal is to understand the working logic of the circuit. It is to make calculations according to the values i want. Is this not possible?
 

ronsimpson

Well-Known Member
Most Helpful Member
understand the working logic of the circuit
The logic is wrong on many levels.

Normally a resistor is places below a LED to measure current. In this case there is a 1 ohm resistor. So 1A going through the LED will cause 1 volt across the resistor. 2mA = 2mV In a working circuit a amplifier compares this voltage to a reference voltage. Example one input of the amp is at a 200mV reference while the other input looks at 200mV across resistor "1R". If the LED current was low, that would cause the voltage on "1R" to be low, example 150mV. The amplifier will see 200-150=50mV of error which get amplified and will force a working PWM to increase the duty cycle.
 

s3rg3n123

New Member
The logic is wrong on many levels.

Normally a resistor is places below a LED to measure current. In this case there is a 1 ohm resistor. So 1A going through the LED will cause 1 volt across the resistor. 2mA = 2mV In a working circuit a amplifier compares this voltage to a reference voltage. Example one input of the amp is at a 200mV reference while the other input looks at 200mV across resistor "1R". If the LED current was low, that would cause the voltage on "1R" to be low, example 150mV. The amplifier will see 200-150=50mV of error which get amplified and will force a working PWM to increase the duty cycle.
thank you for informing me
 

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