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how to determine the amount of current flowing in a circuit

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brunokasimin

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hello,

can somebody explain me (see schematic diagramm as attachment) the amount of current(in ampere) through R2, R4, R3, LA1, LA2, HA1, HA2, LB1, LB2, HB1, HB2, SRA, SRB, LA, LB, HB, HA. The connector J3 is to be connected to a stepper motor, which has maximum current of 0.5 A. J1 is the voltage supply connector and the supply is around 5 V.

I really need help because i'm not good at transistor.i must submit my layout as soon as possible. thanx in advanced
 

Max. I(R3,R4) = 0.25A
Max. I(R2) = 0.5A
I(LA1, LA2, HA1, HA2, ...) = (I think) 0.1A on capacitive transistor load, (zero amper in DC)
I (SRA, SRB) = lower than 100uA

But for accurate values, refer to datasheet of TMC239
 
Re: how to determine the amount of current flowing in a circ

hallo davood,

thx for reply.how did you calculate the values you get? i have read the TMC239 (see Attachment), but one thing i did not understand is the dimension of R2,R3 and R4? R3 and R4 are the sense resistor and R2 is shunt resistor. the formula for sense resistor(Rs)=Voltage Trip/(1.41*Imax). I think Imax is 0.5A(maximum stepper motor current). But how can i calculate the voltage trip?

thx again
 

Re: how to determine the amount of current flowing in a circ

Hi Brunokasimin

Stepper motor has 2 winding, if total motor current is 0.5A then each of which consume 0.25A.
Voltage trip is programmable through SPI interface. Its value change from 0000 to 1111 (or 0-15).
This programmed value first divided to 16 and then multiplied to 0.36V (for 2 volt refrence).
The maximum value of trip voltage will be 0.36*(15/16) = 0.34V.
Now for 0.25A motor winding current Rs = R3 = R4 = 0.34 / Imax = 0.34/0.25= 1.36 ohm
But if each motor winding current was 0.5A then Rs = 0.34/0.5 = 0.68 ohm.

R2 used to protect output driver circuitry, its value as described in datasheet is
R2 = Rsh= 0.1V/(2*Imax) = 0.1V/(2*0.25A) = 0.2 ohm
and for 0.5A for each winding R2=0.1 / (2*0.5) = 0.1 ohm
 
Re: how to determine the amount of current flowing in a circ

haloo davood,

how can we fix so that the current flowing through R2 is 0.5 A? The motor voltage supply is Vm(=5V). In your previous reply, Rsh(oder R2) is 0.1 Ohm.

thx
 

As I mentioned R2 control Maximum amount of current following through output driver circuitry.
If for any reason current go above this limit, output drive circuitry turn off, and protect output transistors.
This limitation is irrelevent to Vm(=5V).
 
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