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Mesuare current without a shunt resistor

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Jundiaí

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shunt resistor pic

Hi friends

I'm using a PIC16F873 to generate a PWM that drive a NMOS transistor that drive a motor DC. But now i need read the current that flow throw the motor and i don't want to use a shunt resistor. Coul you tell another cheap sugestion?

Thanks guys

Jundiaí
 

flatulent

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allegro shunt

There are some indirect ways that measure the voltage drop across any of the parasitic resistances. You can also infer the current from the drain-source drop of the driving FET if it is in saturation. Another way which is more expensive is to use a Hall effect sensor.
 

goodboy_pl

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calculations for shunt resistors

using anti-saturation ckt. (checking drain to source voltage drop to see if it is in saturation region) is a common solution specially at high current which shunt resistor is very lossy or the voltage drop is very low.
it is also used for igbt switches.

BEST!
 

Vauxdvihl

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allegro current shunt

Does anybody have some App-Notes about that ?

Thanks
 

simce

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dc current shunt resistor

You don't need any application note. Simply you are using parasitic resitor that resides on drain-source reginon. Usally you can see drain source region as resistor with constant resistance. Measuring Usd voltage you can "see" what currenti is flowing from drain to source. Becase this voltage is usually small you'll have to aplify it.
Simce
 

Jundiaí

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Thanks guys for the answers.

I have just one more doubt, is it work fine when you are using five or six transistor conect in paralel?

Thanks again

Jundiaí
 

flatulent

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Jundiaí said:
Thanks guys for the answers.

I have just one more doubt, is it work fine when you are using five or six transistor conect in paralel?

Thanks again

Jundiaí

Yes. You should measure the voltage drop across the transistors and the current with a meter temporarily in series. From this you can get the equivalent saturation resistance of the transistors and set the scale factor for your calculations.
 

dpsman

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Check out at Allegro :
**broken link removed**
They've recently released nice current sensor based on Hall efect,
And there is also free samples!!

dpsman
 

sintis

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Isolated current sensors from ZETEX: ZMC05, ZMC10...
 

RegUser_2

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U could use a current transformer (a single loop running through a ferrite ring with multyturn secondary, if your current is AC, else U need a DC current transformer, who besides the AC scheme described also contains additional excitation coil.
 

Fragrance

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Another way which is more expensive is to use a Hall effect sensor.
_________________
yes flatulent is guide you in right way i have done this with centrifuge motor to measure the current used a linear hall effect sensor allgerio
now lanch the new series of hall effect current sensor
 

Moof

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Im using a 3515 allegro hall effect sensor to measure current with the pic. It works perfect once you could determinate the losses in the magnetic circuit.

I read the allegro application notes to build it.

**broken link removed**
**broken link removed**
 

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