Author Topic: 14.4V ground reference for ADC  (Read 12102 times)

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Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #50 on: May 20, 2019, 02:06:08 pm »
Oops, a mistake int the circuit.

I connected  the input of the opamp in reverse :-DD
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #51 on: May 20, 2019, 02:11:10 pm »

I don't want to go in trouble finding the value of the capacitor and resistor and the pwm frequency of the MCU. I will stick with DAC . It will be much more simpler for me.


If you can't do that then you are wasting your time with electronics, it's a free DAC and you are budget constrained yet you are using all of the over the top expensive solutions. What you want to do is feasible provided you do not put anything digihal in a regulation feedback loop. Current limiting you may get away with but there will be a delay.
Its a good idea especially if you are designing a psu with higher power rating. :-+ :-+
I will do this in my next psu project which will be more cheaper :) because it will be high power and low accuracy 
 

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Re: 14.4V ground reference for ADC
« Reply #52 on: May 20, 2019, 03:34:00 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
 
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Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #53 on: May 20, 2019, 03:37:06 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
Can you tell me a part number of any of that smart mosfets?
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #54 on: May 20, 2019, 03:41:39 pm »
I was trying to get rid of that atmega644 and use arduino uno ((atmega328p) which i already have) so i can get the cost down  :-+.
I am trying to put as many things as possible in the I2C.
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #55 on: May 20, 2019, 03:48:21 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
Yes when i simulated the circuit in lt spice i saw a big current spike eventhough i set the constant current.
It was lower than 1ms  so i thought it doesn't matter.
Now i think it does matter.
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #56 on: May 20, 2019, 03:51:00 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
Does adding an inductor before the current shunt help??
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #57 on: May 20, 2019, 03:52:47 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
What can i do about it. I still need to use the DAC.
 

Offline Simon

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Re: 14.4V ground reference for ADC
« Reply #58 on: May 20, 2019, 05:11:06 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
Does adding an inductor before the current shunt help??

NO!
 
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Offline Simon

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Re: 14.4V ground reference for ADC
« Reply #59 on: May 20, 2019, 05:12:48 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
What can i do about it. I still need to use the DAC.

You could learn what you are doing before making stuff up. You have done nothing but emphasize the cost has to be low yet you have thrown parts at this like there is no tomorrow. Why not do the simpler design first that you talked about.
 
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Re: 14.4V ground reference for ADC
« Reply #60 on: May 20, 2019, 05:15:59 pm »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
Can you tell me a part number of any of that smart mosfets?


No I don't. Look them up yourself and learn about them before throwing them around. a smart mosfet datasheet can be 50 pages long. a smart mosfet is not what you want. for example an Infineon mosfet rated for 10A will not cut out through over current for over 50A.
 
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Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #61 on: May 21, 2019, 03:56:12 am »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
What can i do about it. I still need to use the DAC.

You could learn what you are doing before making stuff up. You have done nothing but emphasize the cost has to be low yet you have thrown parts at this like there is no tomorrow. Why not do the simpler design first that you talked about.
I have already done a simpler one a 2 channel PSU with one channel using LM317(1.25-12V)and another with (1-44V) using buck and boost convereter . And with maximum current(two channels)900mA.
It has no current limit.
 

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Re: 14.4V ground reference for ADC
« Reply #62 on: May 21, 2019, 03:57:12 am »
I was refering to your current limits. This is usually done in analogue so reacts instantly. There are smart mosfets that will cut out in 1µs if overloaded. if the current limit does not react fast enough it can still damage stuff.

PWM DAC is easy. the output voltage will be the averaged PWM value, you use a low pass filter that has a cut off frequency 10-100 times lower than the PWM, simple matter of physics.
What can i do about it. I still need to use the DAC.

You could learn what you are doing before making stuff up. You have done nothing but emphasize the cost has to be low yet you have thrown parts at this like there is no tomorrow. Why not do the simpler design first that you talked about.
Yeah, thats my problem ;D :--
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #63 on: May 21, 2019, 04:12:43 am »
I don't understand what you are talking about mosfet :-//
 

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Re: 14.4V ground reference for ADC
« Reply #64 on: May 21, 2019, 05:05:50 am »
The output setling time of the current sense amp is 5µs..And the risetime+ turn on delay time of the irfz44n is only 72ns. and the settling time of the opamp i am using is  1.1µs. So total delay of 6.172µs.Is that a big delay?? :-//
« Last Edit: May 21, 2019, 05:13:50 am by Arjunan M R »
 

Offline Simon

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Re: 14.4V ground reference for ADC
« Reply #65 on: May 21, 2019, 06:27:56 am »
What sort of current limit do you want? you can cut out completely or foldback. For foldback just look it up, there is lots online about it. For cutout you would need a comparator and a latch I think, not something i have done before myself.
 
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Re: 14.4V ground reference for ADC
« Reply #66 on: May 21, 2019, 06:32:05 am »
What sort of current limit do you want? you can cut out completely or foldback. For foldback just look it up, there is lots online about it. For cutout you would need a comparator and a latch I think, not something i have done before myself.
I want foldback current limiting
 

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Re: 14.4V ground reference for ADC
« Reply #67 on: May 21, 2019, 06:35:05 am »
Foldback is easy with SMPS, just measure the current and if you trip a threshold blank the gate drive to the switching element.
 
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Re: 14.4V ground reference for ADC
« Reply #68 on: May 21, 2019, 06:38:36 am »
Foldback is easy with SMPS, just measure the current and if you trip a threshold blank the gate drive to the switching element.
I don't understand  what you mean by blank the gate drive.
 

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Re: 14.4V ground reference for ADC
« Reply #69 on: May 21, 2019, 06:42:11 am »
Foldback is easy with SMPS, just measure the current and if you trip a threshold blank the gate drive to the switching element.
I am not going to change the specifications I choose for the psu.(linear,18V,1A)
 

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Re: 14.4V ground reference for ADC
« Reply #70 on: May 30, 2019, 06:22:32 am »
Hi, I am going to change the voltage reference(2.048V) of my DAC(mcp4922) from ISL21080 to REF3120.I looked at the datasheet and it seems good enough
for my purpose.Note that the DAC voltage ref input is unbuffered.Is there any problem using this v.ref.?
Here is the datasheet please have a look at it.
« Last Edit: May 30, 2019, 06:31:11 am by Arjunan M R »
 

Offline Simon

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Re: 14.4V ground reference for ADC
« Reply #71 on: May 30, 2019, 06:30:38 am »
Your link is brocken, but what you do is look at the output current of the voltage reference in it's datasheet and then look up the input current to the voltage reference pin in the datasheet for the DAC.
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #72 on: May 30, 2019, 06:32:19 am »
Your link is brocken, but what you do is look at the output current of the voltage reference in it's datasheet and then look up the input current to the voltage reference pin in the datasheet for the DAC.
No it is working.When you click on it it will automatically download the pdf file
 

Offline Arjunan M RTopic starter

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Re: 14.4V ground reference for ADC
« Reply #73 on: May 30, 2019, 06:32:58 am »
Your link is brocken, but what you do is look at the output current of the voltage reference in it's datasheet and then look up the input current to the voltage reference pin in the datasheet for the DAC.
Ok
 

Offline Simon

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Re: 14.4V ground reference for ADC
« Reply #74 on: May 30, 2019, 06:35:17 am »
Your link is brocken, but what you do is look at the output current of the voltage reference in it's datasheet and then look up the input current to the voltage reference pin in the datasheet for the DAC.
No it is working.When you click on it it will automatically download the pdf file

No it was brocken and you just edited it! If that is your attitude good luck learninig electronics. Maybe you want to try lego bricks where everything is made for each other and nothing can go wrong!
 


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