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High current Voltage Regulator

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tim90

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Hi to everybody, I wanted to ask something regarding a project that I'm doing. I need a power supply for my circuit that must be equal to 3.3V and up to 25A. The main problem is that i am doing an anolog sensitive device in which i need a stable voltage.If I have a voltage difference more the 10mV, my circuit will change completely its behaviour. I'don't need a precise 3.3V but it must remain stable. If i have 3.2 it is good, but only if it remain stable and it is not easy to find a device able to ensure a stable voltage with this high current. Do you know some IC for my applications? my idea was to use a personal computer power supply to get 5V and high current but the i need a voltage regulator for the 3.3v and able to substain this high current, for example the lm 1084 but whit a maximum uotput current 5 times higher. If you have some ideas but instead of 25A i can reach only 8 or 10 or more amps, let me know, because i can start by considering for examples half of the maximum power of my circuit. Thanks a lot for who will answer.
 
Does the whole circuit need to have a stable voltage or just part of it?
Does the current vary during the test?
 
just a part of it, I have a part that is controlled by the freescale board and then another part in which i need this power. The current vary during the test. I forgot to say another important thing, i can not use the pwm technics because there are some electrode in the circuit and the pwm will create noise.
 
Hi to everybody, I wanted to ask something regarding a project that I'm doing. I need a power supply for my circuit that must be equal to 3.3V and up to 25A. The main problem is that i am doing an anolog sensitive device in which i need a stable voltage.If I have a voltage difference more the 10mV, my circuit will change completely its behaviour. I'don't need a precise 3.3V but it must remain stable. If i have 3.2 it is good, but only if it remain stable and it is not easy to find a device able to ensure a stable voltage with this high current. Do you know some IC for my applications? my idea was to use a personal computer power supply to get 5V and high current but the i need a voltage regulator for the 3.3v and able to substain this high current, for example the lm 1084 but whit a maximum uotput current 5 times higher. If you have some ideas but instead of 25A i can reach only 8 or 10 or more amps, let me know, because i can start by considering for examples half of the maximum power of my circuit. Thanks a lot for who will answer.

Hy tim,

Welcome to ETO.

I'm afraid what you are asking for would involve a power supply with remote sensing and even then you would not get the performance you say you need, but if you give a circuit and description of what you are trying to do I suspect we could help.
 
From TDK
Part number RTW0325R
3.3V 25A 100W
85 to 265 Vac input.
**broken link removed**
 
just a part of it, I have a part that is controlled by the freescale board and then another part in which i need this power. The current vary during the test. I forgot to say another important thing, i can not use the pwm technics because there are some electrode in the circuit and the pwm will create noise.
So are you saying that only part of the circuit needs to have this stable voltage?
If so, then you just a good regulator for that portion of the current.
 
Could you handle separately power and signal so this last can keep within the allowed window?
 
I attached only a part of the circuit. The 3.3V is the power supply that i need. The circuit is composed by 16 of this element, so 16r_sense, 16 current regulator and 16 R from r_1 to r_16, at each segment i have a maximum current of 1.5A. The current regulator, control the current basically, and it is controlled by the freescale board. I resistor at the bottom part has a value form 0.35 to 0.5 ohno and this value depends on the temperature. I need to know the value of this resistance at each moment, for this reason I compute the voltage drop across it by using the ADC and than, knowing the current and can compute the value of the resistance. But I need to know the value of the current with high precision. I compute the current by software, in particular, the current is equal to (3.3v - Vr_sense)/0.22. Now, if instead of having 3.3v, I have 3.25 volt, I will have a different current respect the current computed by software and so an error when i compute the resistance. So I need maximum error of 10 mV more or less. As i have said i don't need 3.3v precise but i need a stable value. More over i need a power supply like the RTW0325R and not big like the Sorensen XHR Series because my device should be portable. Last thing, my first idea was to use a pc power supply but i think that it is not so precise. I am sorry, i know that usually i am not very clear and my english is not perfect.
 

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A PC power supply probably has many outputs and will not regulate as good. Use a single output power supply.
Most power supplies are good at holding the voltage constant.
Your load is about the same all the time. This will help the power supply keep the same voltage.
You can measure the 3.3V every time in your software. If the 3.3V changes you can remove the effect in software.
You might have more voltage lost in the wire then you think.
The specifications for a power supply might read; 1A to 25A with 20mV change in voltage. But your current is 24 to 45A so the voltage will change very little.
 
It looks like R1 and R2 could dissipate over 1 W each. Won't that self-heating affect the temperature reading?

ak
 
Ron's suggestion seems good.
Just measure the 3.3V before you do the current measurement.
 
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