5A Constant Voltage/Constant Current Regulator
5A Constant Voltage/Constant Current Regulator
Thank you for reading this post. I have built the charging circuit below on a breadboard and have tested the voltage adjustment and it works great. I can not figure out how to test the current side. So, my two questions are these. How can I test the current adjustment and how does this circuit adjust the current through MJ4502? It would seem to me that the pot should be at the base of the MJ4502.
Hi there,
You do not need nor want to have a pot at the base of the MJ4502.
Doing so would lead to the current setting changing for various
reasons such as input supply voltage change. The circuit, as is,
provides a current limit setting that should not change for almost
any input voltage and load.
The circuit, as is...
The MJ4502 transistor is under complete control by the LM317, and the
LM317 is under control by either the voltage pot or the current pot
via the LM301 op amp. The current adjust pot sets the R2/R5
divider voltage at pin 2 of the LM301, and when this voltage
becomes greater than the output voltage current limit starts
to take place. This schematic looks ok and should work ok.
Diode D1 acts as an 'analog' OR logic function, allowing
voltage control when the LM301 is not trying to control but
allowing the LM301 to take control of the LM317 when the current
rises up enough to raise pin 2 higher than pin 3.
Of course when current limit kicks in the LED should light up.
My guess is that there should not be a problem with using
another type of op amp either, such as the LM358.
There are simpler circuits to do the same thing, using low
side current sensing.
To test the current limit function you connect a load that draws
at least 6 amps and measure the current while rotating the current
limit pot. The current should go up and down. With the arm in
one direction you should get about 5 amps. With the arm about
half way you should get around 1.7 amps (approximate). With
the arm adjusted the other way you may get very very low
current (almost zero or zero).
You do not need nor want to have a pot at the base of the MJ4502.
Doing so would lead to the current setting changing for various
reasons such as input supply voltage change. The circuit, as is,
provides a current limit setting that should not change for almost
any input voltage and load.
The circuit, as is...
The MJ4502 transistor is under complete control by the LM317, and the
LM317 is under control by either the voltage pot or the current pot
via the LM301 op amp. The current adjust pot sets the R2/R5
divider voltage at pin 2 of the LM301, and when this voltage
becomes greater than the output voltage current limit starts
to take place. This schematic looks ok and should work ok.
Diode D1 acts as an 'analog' OR logic function, allowing
voltage control when the LM301 is not trying to control but
allowing the LM301 to take control of the LM317 when the current
rises up enough to raise pin 2 higher than pin 3.
Of course when current limit kicks in the LED should light up.
My guess is that there should not be a problem with using
another type of op amp either, such as the LM358.
There are simpler circuits to do the same thing, using low
side current sensing.
To test the current limit function you connect a load that draws
at least 6 amps and measure the current while rotating the current
limit pot. The current should go up and down. With the arm in
one direction you should get about 5 amps. With the arm about
half way you should get around 1.7 amps (approximate). With
the arm adjusted the other way you may get very very low
current (almost zero or zero).
LEDs vs Bulbs, LEDs are winning.
GREEEEEEEAAAT circuit. . . . as Tony the Tiger would say. . . .
Used it ever since the data sheet came out on it back in the 70-80's, and even using the IC forerunners of the LM 317's, before that time frame..
There is a better circuit using two '350's with the second one handling the current aspects.
Consulting the marked up thumbnail you can see that the RED buss is the normal '317 circuitry, but in viewing the orange buss you will see that they have piggy backed in the MJ4502 so that it is sampling the current across R1 and then tracking and performing the bulk of the power handling with the '317 circuitry just loafing . . . .BUT. . . marvelously performing all of its built in overload-over temp-shutoff-functions of the circuitry.
Check the green buss and you will observe that it is merely sampling the loading presented across the R3 current shunt resistor and feeding correction to the negative node of the '301 op amp which then its tailors the output for the current correction action.
Current set up:
If you are wanting to apply a limited current to an unknown test/ prototype circuit, such that something might be damaged, the
usual procedure is to have the voltage control set for being a bit more than you will be needing and then swing the current adjust to the minimum position and have a DC milliameter / ammeter totally shorting across your power supply's output and then you slowly raise the CURRENT ADJUST up to the max that you will be wanting.
Then remove the current metering and confirm your voltage under load and you are in business .
Should you find that the circuitry loading is already pulling your supply down a bit, you can just adjust the CURRENT ADJUST upwards
until your needs are met, just double check your voltage output also.
REFERENCING:
73's de Edd
[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
All that glitters. . . . . has a high refractive index !
Used it ever since the data sheet came out on it back in the 70-80's, and even using the IC forerunners of the LM 317's, before that time frame..
There is a better circuit using two '350's with the second one handling the current aspects.
Consulting the marked up thumbnail you can see that the RED buss is the normal '317 circuitry, but in viewing the orange buss you will see that they have piggy backed in the MJ4502 so that it is sampling the current across R1 and then tracking and performing the bulk of the power handling with the '317 circuitry just loafing . . . .BUT. . . marvelously performing all of its built in overload-over temp-shutoff-functions of the circuitry.
Check the green buss and you will observe that it is merely sampling the loading presented across the R3 current shunt resistor and feeding correction to the negative node of the '301 op amp which then its tailors the output for the current correction action.
Current set up:
If you are wanting to apply a limited current to an unknown test/ prototype circuit, such that something might be damaged, the
usual procedure is to have the voltage control set for being a bit more than you will be needing and then swing the current adjust to the minimum position and have a DC milliameter / ammeter totally shorting across your power supply's output and then you slowly raise the CURRENT ADJUST up to the max that you will be wanting.
Then remove the current metering and confirm your voltage under load and you are in business .
Should you find that the circuitry loading is already pulling your supply down a bit, you can just adjust the CURRENT ADJUST upwards
until your needs are met, just double check your voltage output also.
REFERENCING:
73's de Edd
[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
All that glitters. . . . . has a high refractive index !
Thank you both for your reply's.
I hooked up a DC motor and adjusted the current limiting
pot from full resistance to no resistance but had no change.
The reason the current limiting pot is important to me is
to protect the power supply not the rest of the circuit. I
am charging 2 two farad caps and when they charge they
draw a large amount of current. My power supply can only
handle 3.6A. I pulled this power supply from an ultrasound.
I tested the circuit using a stand alone power supply with
current limiting capabilityies to test the circuit and it works great.
However, it is a large supply so I dont want to use it permanently.
I hooked up a DC motor and adjusted the current limiting
pot from full resistance to no resistance but had no change.
The reason the current limiting pot is important to me is
to protect the power supply not the rest of the circuit. I
am charging 2 two farad caps and when they charge they
draw a large amount of current. My power supply can only
handle 3.6A. I pulled this power supply from an ultrasound.
I tested the circuit using a stand alone power supply with
current limiting capabilityies to test the circuit and it works great.
However, it is a large supply so I dont want to use it permanently.
.
I hooked up a DC motor and adjusted the current limiting
pot from full resistance to no resistance but had no change
The question here is, what is the STARTING current requirements
on that motor. Considering it to be a DC motor with brushes,
the initial starting current is fierce and then progressively
tapers down at the speed picks up and then settles down until
there is then any mechanical loading presented to the motor.
Soooo. . . . is this the same manner of testing (motor) that
you subjected the power supply to when you commented with:
I tested the circuit using a stand alone power supply with
current limiting capabilities to test the circuit and it
works great.
If so we might consider that the mere:
My power supply can only handle 3.6A.
Is being inadequate to get the motor initially running, so you
would not be subjecting the circuit to the same parameters.
Is this a possibility, if so try using a resistive load that
would only be pulling about 2-3 amps to test the circuit with that
power supply for an evaluation that way.
HOWEVER, if the real utilization of this power supply combo is
to charge up a high value capacitance bank , it would be acting
just about like hitting that motor.
The difference being, that the cap storage bank would be progressively
taking on a charge constantly and the voltage building up.
In the case of your non- moving motor it is just standing there and
taking in ALL of the current being presented to it.
73's de Edd
[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
If debugging is the process of removing bugs, then programming must be the process of putting them in!
.
I hooked up a DC motor and adjusted the current limiting
pot from full resistance to no resistance but had no change
The question here is, what is the STARTING current requirements
on that motor. Considering it to be a DC motor with brushes,
the initial starting current is fierce and then progressively
tapers down at the speed picks up and then settles down until
there is then any mechanical loading presented to the motor.
Soooo. . . . is this the same manner of testing (motor) that
you subjected the power supply to when you commented with:
I tested the circuit using a stand alone power supply with
current limiting capabilities to test the circuit and it
works great.
If so we might consider that the mere:
My power supply can only handle 3.6A.
Is being inadequate to get the motor initially running, so you
would not be subjecting the circuit to the same parameters.
Is this a possibility, if so try using a resistive load that
would only be pulling about 2-3 amps to test the circuit with that
power supply for an evaluation that way.
HOWEVER, if the real utilization of this power supply combo is
to charge up a high value capacitance bank , it would be acting
just about like hitting that motor.
The difference being, that the cap storage bank would be progressively
taking on a charge constantly and the voltage building up.
In the case of your non- moving motor it is just standing there and
taking in ALL of the current being presented to it.
73's de Edd
[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
If debugging is the process of removing bugs, then programming must be the process of putting them in!
.
Let me start from the beginning because I don’t think I have given enough information to adequately inform you on how to help.
Sorry.
I am building a capacitor welder. I am using 2 two farad capacitors and an SCR to do the work. I have been charging the caps using
a Tenma laboratory DC power supply. It has current limiting capabilities and over current protection. I want to have a standalone
system all in one box so I am trying to build a simple supply. I chose the circuit above in hopes of being able to adjust the current
flow down so not to destroy this circuit as well as the separate power supply I removed from an ultrasound. When charging the
caps with the Tenma I see the current peg the max at 5A until the voltage comes up then the current quickly goes to zero. So I
actually don’t know how much current would be pulled if not for the Tenma’s current limiter. The power supply I removed
from the ultrasound is a 120v input 28v output Power-One model SF28-3.6.
Thank you for your help!!
Al, pins number 4, 5, and 7 are not connected.
Sorry.
I am building a capacitor welder. I am using 2 two farad capacitors and an SCR to do the work. I have been charging the caps using
a Tenma laboratory DC power supply. It has current limiting capabilities and over current protection. I want to have a standalone
system all in one box so I am trying to build a simple supply. I chose the circuit above in hopes of being able to adjust the current
flow down so not to destroy this circuit as well as the separate power supply I removed from an ultrasound. When charging the
caps with the Tenma I see the current peg the max at 5A until the voltage comes up then the current quickly goes to zero. So I
actually don’t know how much current would be pulled if not for the Tenma’s current limiter. The power supply I removed
from the ultrasound is a 120v input 28v output Power-One model SF28-3.6.
Thank you for your help!!
Al, pins number 4, 5, and 7 are not connected.
.
Good thing that you filled us in, and you just must have imagined that power supply current limiting
having been working before when you bench tested it out with the other power supply. In which case
then, any current limiting would have solely been attributable to the '317's controlling circuitry.
Also, your failure of the current control of the power supply that you built is directly attributable to
your not supplying it with the diferential supply voltages of + 6 VDC and - 6 VDC in this case.<br>
NO poweree. . . .No workee.<br>
As simple as using the smallest...current rated.... 12 VAC center tapped "filament" transformer that
you can find, and a set of diodes and a pair of 220-470 ufd filters to make a + - supply which would
then actually be up in the + -9 V or so range, but no problem with that. THEN you get those voltages
connected to the two power supply nodes that you left floating, and the circuit should talk to you then.
HOWEVER !
With you having given us that Power One reference #, I think that you could just fly with
the unit as it is, with a high current diode in series from the power supply to the cap bank circuit
for its isolation.
The reason that I say that is, in my dealings with Power One supplies in the past , as was being
used on mock up prototypes at NASA, they had current limiting and foldback current limiting designed into the units.
Granted, that the only ones that I used were the linear series, as shown in my A and B pic
references with the B and C pics being switch mode designs ( which is probably what you have).
But looking up your numbered unit given, it is priced up in the $500-600 dollar range and they even
want ~$297 for a rebuild on one.
So apparently, your little hands have come up fondling, not the typical little $99 . . .28volt 3.6 amp linear power supply.
73's de Edd
[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
Buy Vista. . . . so you can reboot faster !
.
Good thing that you filled us in, and you just must have imagined that power supply current limiting
having been working before when you bench tested it out with the other power supply. In which case
then, any current limiting would have solely been attributable to the '317's controlling circuitry.
Also, your failure of the current control of the power supply that you built is directly attributable to
your not supplying it with the diferential supply voltages of + 6 VDC and - 6 VDC in this case.<br>
NO poweree. . . .No workee.<br>
As simple as using the smallest...current rated.... 12 VAC center tapped "filament" transformer that
you can find, and a set of diodes and a pair of 220-470 ufd filters to make a + - supply which would
then actually be up in the + -9 V or so range, but no problem with that. THEN you get those voltages
connected to the two power supply nodes that you left floating, and the circuit should talk to you then.
HOWEVER !
With you having given us that Power One reference #, I think that you could just fly with
the unit as it is, with a high current diode in series from the power supply to the cap bank circuit
for its isolation.
The reason that I say that is, in my dealings with Power One supplies in the past , as was being
used on mock up prototypes at NASA, they had current limiting and foldback current limiting designed into the units.
Granted, that the only ones that I used were the linear series, as shown in my A and B pic
references with the B and C pics being switch mode designs ( which is probably what you have).
But looking up your numbered unit given, it is priced up in the $500-600 dollar range and they even
want ~$297 for a rebuild on one.
So apparently, your little hands have come up fondling, not the typical little $99 . . .28volt 3.6 amp linear power supply.
73's de Edd
[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
Buy Vista. . . . so you can reboot faster !
.
reckerd wrote:
Al, pins number 4, 5, and 7 are not connected.
Hi again,
You need to connect pins 7 and 4 or it will never work.
Pin 7 has to go to the most positive supply (+35v) and
pin 4 has to go to a negative supply source. You definitely
need these two connected.
What is the needed max output voltage for this app?
LEDs vs Bulbs, LEDs are winning.
Hello,
I would like to make sure of something. I connect pin 7 to input source which is 28vdc. Can I connect pin 4 to -12vdc?
I have another power supply that I can use that has more output voltage sources. +12, -12, +5, +24vdc. This unit is a Lambda 2D4WB1A-1467.
I just didnt know if I should use it. It is kind of like using a sledge hammer to kill a gnat.
Edd brought up another question. What rating of diode should I use between the caps and power supply?
24vdc is the max surge rating for the caps. I was going to max the output at 20vdc.What is the needed max output voltage for this app?
I would like to make sure of something. I connect pin 7 to input source which is 28vdc. Can I connect pin 4 to -12vdc?
I have another power supply that I can use that has more output voltage sources. +12, -12, +5, +24vdc. This unit is a Lambda 2D4WB1A-1467.
I just didnt know if I should use it. It is kind of like using a sledge hammer to kill a gnat.
Edd brought up another question. What rating of diode should I use between the caps and power supply?
Hi again,
You can use that supply for the -12v output, but you should
regulate it down to -6v for this circuit because with the
positive supply reaching as high as 28vdc and with any ripple
and a -12v supply depending on what manufacturer made your
LM301 you could kill it. Some LM301A's are made to handle
+/- 22v (44v total) while others will only handle
+/- 18v (36v total). 28+12=40v, so you would have to make sure
you had the right manu to do this. If you use a -6v regulator
you can connect that to -12 and power your circuit from its
output. Of course at some point you can invest in a small
minus supply generator circuit to get the -6v supply, once you
get everything up and running.
If you want to use a diode between main supply and this regulator
and you intend to draw 3 amps max then a 5 amp diode should
handle your load ok, unless you want to try a 3 amp device
and see if it holds up first, like 1N5404 or something.
You'll need to follow the board layout and soldering technique
very carefully for this diode however, or else just use a 5 amp
device and be done with it (maybe with a small heat sink).
If i knew all you really needed was a current limiter i think
we could have come up with a MUCH simpler circuit than this one,
most likely not requiring any other power supplies.
Is it possible to reduce the voltage from 28vdc down to 20vdc
with the main power supply you are using (not this one)?
You can use that supply for the -12v output, but you should
regulate it down to -6v for this circuit because with the
positive supply reaching as high as 28vdc and with any ripple
and a -12v supply depending on what manufacturer made your
LM301 you could kill it. Some LM301A's are made to handle
+/- 22v (44v total) while others will only handle
+/- 18v (36v total). 28+12=40v, so you would have to make sure
you had the right manu to do this. If you use a -6v regulator
you can connect that to -12 and power your circuit from its
output. Of course at some point you can invest in a small
minus supply generator circuit to get the -6v supply, once you
get everything up and running.
If you want to use a diode between main supply and this regulator
and you intend to draw 3 amps max then a 5 amp diode should
handle your load ok, unless you want to try a 3 amp device
and see if it holds up first, like 1N5404 or something.
You'll need to follow the board layout and soldering technique
very carefully for this diode however, or else just use a 5 amp
device and be done with it (maybe with a small heat sink).
If i knew all you really needed was a current limiter i think
we could have come up with a MUCH simpler circuit than this one,
most likely not requiring any other power supplies.
Is it possible to reduce the voltage from 28vdc down to 20vdc
with the main power supply you are using (not this one)?
LEDs vs Bulbs, LEDs are winning.
If there is a much simpler way then I am not married to this circuit.
The bottom line is I need to have a way to charge the 2 two farad capacitors at voltages ranging from @ 6vdc-@20vdc.
The only purpose of me wanting to control the current is to protect both of my circuits.
(one the power supply, two the voltage adjusting circuit).
When the caps charge they draw a large amount of current.
As far as the diode goes I am not sure how much current will be drawn between the voltage adjusting circuit and the caps. If I can
slow the current down then I will get a 5 amp diode to keep the caps from feeding back into the voltage control circuit.
The bottom line is I need to have a way to charge the 2 two farad capacitors at voltages ranging from @ 6vdc-@20vdc.
The only purpose of me wanting to control the current is to protect both of my circuits.
(one the power supply, two the voltage adjusting circuit).
When the caps charge they draw a large amount of current.
As far as the diode goes I am not sure how much current will be drawn between the voltage adjusting circuit and the caps. If I can
slow the current down then I will get a 5 amp diode to keep the caps from feeding back into the voltage control circuit.
Hi again,
The simpler circuit i have in mind would use a setup like you already
have (so most of the work you've already done) but will replace
the LM301 with a small transistor and two 5 amp diodes and a couple
resistors. This way you dont need the LM301 (which could be blown at
this point) and you dont need the negative supply source, and everything
else stays the same (LM317, MJ4502 transistor).
If this sounds interesting i will post a schematic.
LATER...
I threw this together. Note the current limit is adjusted by the resistor
shown. We can add a pot if you really really need one later.
The simpler circuit i have in mind would use a setup like you already
have (so most of the work you've already done) but will replace
the LM301 with a small transistor and two 5 amp diodes and a couple
resistors. This way you dont need the LM301 (which could be blown at
this point) and you dont need the negative supply source, and everything
else stays the same (LM317, MJ4502 transistor).
If this sounds interesting i will post a schematic.
LATER...
I threw this together. Note the current limit is adjusted by the resistor
shown. We can add a pot if you really really need one later.
LEDs vs Bulbs, LEDs are winning.
Hi again,
Oh good, cant wait to hear your results.
One thing i didnt mention on the schematic was that if the output
current was going to be set for less than 5 amps (like 3 amps)
it would probably be possible to use a lower rated diode for D20,
especially like 1 amp output, where a 1N5402 would ceratainly work
well. At 5 amps continuous though, i might use a higher rated diode
(your app will not be continuous) like 7 or 8 amps.
At 3 amps and not continuous a 1N5402 diode might work, but
again a higher rated diode would be better, like 5 amps.
I am mentioning this because i think you wanted to use 3 amps
max to charge your caps.
Also, because of the diode you may not need another diode
for isolation.
Oh good, cant wait to hear your results.
One thing i didnt mention on the schematic was that if the output
current was going to be set for less than 5 amps (like 3 amps)
it would probably be possible to use a lower rated diode for D20,
especially like 1 amp output, where a 1N5402 would ceratainly work
well. At 5 amps continuous though, i might use a higher rated diode
(your app will not be continuous) like 7 or 8 amps.
At 3 amps and not continuous a 1N5402 diode might work, but
again a higher rated diode would be better, like 5 amps.
I am mentioning this because i think you wanted to use 3 amps
max to charge your caps.
Also, because of the diode you may not need another diode
for isolation.
LEDs vs Bulbs, LEDs are winning.
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