voltage and current regulator curcuit that have problems

Thread Starter

psoke0

Joined Mar 31, 2017
174
hello guys this is the curcuit i have build.

1624668030752.png

supply voltage is 12 V
the curcuit works just fine with simulation and i build it in real pcb. i adjust VR1 and set output voltage to be 1 volt. and i adjust VR2 to be as much current its can give it is 10 k pot. its works with 6.7 Amps voltage drops of course but its okay. the problem is when i lower the R6 more and curcuit should draw more then 6.7 or about. the curcuit instead of just staying at 6.7 amps like i adjusted to be its not. its just drops below 2 amps even it drops to 0.02 amps . i mean voltage at R7 of course gets higher then set voltage and makes IC (bbb ) output to HIGH and that makes Q2 operate and makes Q1 shut down so the current drops. i get that. but when that happens R7 voltage drops below set voltage , IC bbb should cut off the base voltage and it should still try to give me the current i set it to 6 amps or so . is that wrong ? can you guys help me please .
 

Papabravo

Joined Feb 24, 2006
17,316
This sounds like an attempt to control both current and voltage at the same time. Is that what is going on or am I missing something?
Is there a reason why you have R4 and R6 in parallel with each other? You get the same result by eliminating the 1K resistor R4. It serves no useful function that I can see.
 

Thread Starter

psoke0

Joined Mar 31, 2017
174
This sounds like an attempt to control both current and voltage at the same time. Is that what is going on or am I missing something?
Is there a reason why you have R4 and R6 in parallel with each other? You get the same result by eliminating the 1K resistor R4. It serves no useful function that I can see.
R4 is allways going to be there for measure the voltage when there is no load ( R6 ) R6 is the external load

and yes i am trying to control both voltage and current at the same time :/
 

LowQCab

Joined Nov 6, 2012
1,372
You can't control Voltage and Current at the same time.
You can control the Voltage,
and then reduce or turn-off the Voltage if a certain set amount of Current is measured.

Are you trying to create an LED Power-Supply ?,
if so, what You need is called a "Current-Source", or, a "Current-Sink",
with these types of Supplies, regulating the Voltage is usually not necessary.
==========================================================

R-4 does nothing, remove it.

Q-1 should have it's Gate Grounded by a 100-K Resistor, NOT pulled-up to 12-V.

You don't need a Transistor on the Gate of Q-1,
drive Q-1's Gate directly with the Op-Amp(s).

Where is the Load for this Regulator ??????

R-9, and R-10 are unnecessary, remove them.

Both IC-1a, and IC-1b, are both setup as Comparitors, not Op-Amps,
they will either be On or Off,
so if You ever got this Circuit to do anything,
it would just immediately go into oscillation.
.
Here is your schematic cleaned up some and with a few changes to make it legible.
.
1624668030752.png
 

Papabravo

Joined Feb 24, 2006
17,316
R4 is allways going to be there for measure the voltage when there is no load ( R6 ) R6 is the external load

and yes i am trying to control both voltage and current at the same time :/
That is an incorrect statement. The parallel combination will behave as if R4 is not even there.
Ohm's law will prevent from controlling the voltage and the current in a circuit at the same time. The best you can hope to achieve is to control one of them and limit the other.
 

Thread Starter

psoke0

Joined Mar 31, 2017
174
You can't control Voltage and Current at the same time.
You can control the Voltage,
and then reduce or turn-off the Voltage if a certain set amount of Current is measured.

Are you trying to create an LED Power-Supply ?,
if so, what You need is called a "Current-Source", or, a "Current-Sink",
with these types of Supplies, regulating the Voltage is usually not necessary.
==========================================================

R-4 does nothing, remove it.

Q-1 should have it's Gate Grounded by a 100-K Resistor, NOT pulled-up to 12-V.

You don't need a Transistor on the Gate of Q-1,
drive Q-1's Gate directly with the Op-Amp(s).

Where is the Load for this Regulator ??????

R-9, and R-10 are unnecessary, remove them.

Both IC-1a, and IC-1b, are both setup as Comparitors, not Op-Amps,
they will either be On or Off,
so if You ever got this Circuit to do anything,
it would just immediately go into oscillation.
.
Here is your schematic cleaned up some and with a few changes to make it legible.
.
View attachment 242151
R9 and R10 is there after i see the 3 of LM358 chips are having problems internally. they had 100 ohms or about resistance pins in the inverting and other pin . after adding them Chip never failed again. i dont know what coused that chips failed like that that made no sense to me but after adding them problem solved. this is not led driver. its lab bench power supply. the load of this curcuit is external load R6 which resistance of it changes depends on the load. isnt oscillation a good thing here ? because its will allways try to set the current and voltage i set it to
 

Thread Starter

psoke0

Joined Mar 31, 2017
174
That is an incorrect statement. The parallel combination will behave as if R4 is not even there.
Ohm's law will prevent from controlling the voltage and the current in a circuit at the same time. The best you can hope to achieve is to control one of them and limit the other.
i actually want what you are saying. i will just set the voltage to 1 volt for example and set the current to 5 amps. and curcuit can go into constant current mode and drop the voltage its okay that what should happen . as long as voltage doesnt go above the set voltage its okay.
 

LowQCab

Joined Nov 6, 2012
1,372
The way you are trying to do this will not work.

You say that You want a Bench-Power-Supply,
OK, fine,
now you have to define the Output specifications that You expect it to able to deliver.

Do You already have a Transformer ?, if so, what are the specifications of the Transformer ?,
or,
do You intend to use a Battery ?, what type of Battery ?
or,
do You intend to purchase a new Transformer, or Battery,
to meet your expected Output-Specifications ?

What is the Maximum Voltage that You expect to need ?
What is the Maximum Current that You expect to need ?
Will You need a "Split-Power-Supply" with a "Plus-Ground-Minus" type Output ?

You can't even start the designing of a Power-Supply without
answering all of these questions completely.
.
.
.
 

Thread Starter

psoke0

Joined Mar 31, 2017
174
The way you are trying to do this will not work.

You say that You want a Bench-Power-Supply,
OK, fine,
now you have to define the Output specifications that You expect it to able to deliver.

Do You already have a Transformer ?, if so, what are the specifications of the Transformer ?,
or,
do You intend to use a Battery ?, what type of Battery ?
or,
do You intend to purchase a new Transformer, or Battery,
to meet your expected Output-Specifications ?

What is the Maximum Voltage that You expect to need ?
What is the Maximum Current that You expect to need ?
Will You need a "Split-Power-Supply" with a "Plus-Ground-Minus" type Output ?

You can't even start the designing of a Power-Supply without
answering all of these questions completely.
.
.
.
the specifications is not really that much matters. because the power supply i use is computer power supply that can handle about 15 amps at 12 volts. i dont want to go above that. i just want to go as far as my computer power supply can handle if not less. so if its gives me from 0 volts to 10 volts even 5 volts its okay. if its gives 0 amps to 5 amps its okay. this power supply will just be for the finding short curcuits that cant handle more then 1 volt for example. so i set it to 1 volt and current to 3 amps. and find if it is short to ground or not. and also i tried the new design you provided and yes its much better to drive the mosfet directly thank you but it didnt work well so i changed it a bit its fine now i set the voltage to 1 volt and limit the current by dragging base of mosfet down. i dont know if this will work in real i have to test it

1624689783358.png
 

LowQCab

Joined Nov 6, 2012
1,372
15-Amps X 12-Volts = 180-Watts of Heat,
that Heat can be Dissipated by the Part being Powered, or
it must be Dissipated by the MOSFET,
so you need a large Heat-Sink with a Fan to make sure that You don't smoke the FET.

Your changes will not work,
especially if You expect to have well Filtered Power Control.
When I get some free-time,
I'll make You a Schematic that will have very reasonable performance and Control.
.
.
.
 

LowQCab

Joined Nov 6, 2012
1,372
If you don't have a 1K Pot for the Current-Control,
make sure that you multiply the 665-Ohm Precision-Resistor by the same factor.
For instance, if You use a 10K-Pot, then You need to multiply the 665R-Resistor by 10,
making it a 6,650R, or 6.65K, or 6K65.

The Voltage Pot doesn't matter, as long as it's between 1K and 100K.

If the Output tends to want to oscillate under certain circumstances,
put 10-1,000uf, 50-Volt-Rated Capacitors, wired in parallel, across the Output-Terminals.
This is absolutely necessary if you are going to be Powering any Motors with this Regulator.
The Brushes in a Motor create tons of RFI-Noise which could easily smoke that expensive FET.
.
.
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Thread Starter

psoke0

Joined Mar 31, 2017
174
If you don't have a 1K Pot for the Current-Control,
make sure that you multiply the 665-Ohm Precision-Resistor by the same factor.
For instance, if You use a 10K-Pot, then You need to multiply the 665R-Resistor by 10,
making it a 6,650R, or 6.65K, or 6K65.

The Voltage Pot doesn't matter, as long as it's between 1K and 100K.

If the Output tends to want to oscillate under certain circumstances,
put 10-1,000uf, 50-Volt-Rated Capacitors, wired in parallel, across the Output-Terminals.
This is absolutely necessary if you are going to be Powering any Motors with this Regulator.
The Brushes in a Motor create tons of RFI-Noise which could easily smoke that expensive FET.
.
.
.
thank you . i want to ask for learning. why did you use negative feedback configuration . why not use it like a comparator what is the differance
 

LowQCab

Joined Nov 6, 2012
1,372
There are 2-Flavors of Regulators,
Linear, which is what you've been working with, and
Switch-Mode-Regulators,
which turn either fully On, or, fully Off, usually at very high Frequencies.

Both use Voltage-Feedback,
and depending on the design,
they may also use Current-Feedback.

Switch-Mode-Regulators require a properly designed Filter-Network on the Output,
but generally speaking,
most Linear-Regulators can be run with no Filtering of the Output.

If a Switching-Regulator is run without a proper Filter-Network,
all kinds of crazy problems are created,
and you will basically have really BAD Voltage-Regulation, and a ton of Electrical "Noise".
You might get away with this if your Load is strictly Resistive,
like a Heating-Element, or an Incandescent-Light-Bulb,
but if there is the slightest amount of Inductance, or Capacitance, in your Load,
you will have serious problems.

Switching-Regulators are usually much more efficient,
and therefore, they Dissipate much less Heat than a Linear-Regulator.

To make a Switch-Mode-Regulator work,
there is usually some additional complexity and Cost -vs- a Linear-Regulator's simplicity.

Also, many Op-Amps can NOT deal with being used as a Comparitor,
especially at High-Frequencies.

The LM358's that You were trying to use are ~$0.10 Cents each,
they are for very un-demanding jobs were CHEAP is the Top-Priority.

The LT1630CN8 Op-Amps that I specified are
the closest thing to a perfect Op-Amp that I've found,
and they ought to be, because the damn things cost ~$8.oo each,
but they have excellent manners in all situations,
so they're very easy to work with.
They will operate as a Comparitor at over 100khz without issues,
and have "Rail-to-Rail" Inputs and Outputs,
which also makes them work really well for DC-Circuits.
And, they're still available in a Through-Hole, 8-Pin-DIP-Package,
which makes them Hobbyist-Friendly.

If you are willing to spend another ~$40 to ~$50 Dollars,
I'll show You how to DIY your own Switch-Mode-Regulator.
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