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Current monitor/sensor

### Author Topic: Current monitor/sensor  (Read 12255 times)

#### audioguru

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##### Re: Current monitor/sensor
« Reply #14 on: November 04, 2012, 05:23:04 PM »
I do not know why you are doing things completely differently to the circuits in the datasheet of the IC.

#### denci

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##### Re: Current monitor/sensor
« Reply #15 on: November 05, 2012, 03:43:45 PM »
I made a battery analyzer, which can analyze the battery and discharge it. I can set up the discharge current with pwm controled voltage regulated through resistor. Voltage on resistor limitc the current, which flow from battery. I did the mistake and i put ZXCT at the end of circuit, because i was not careful what is show in datasheet. This analyzer would also be possibility of charge the baterry and all circuit swithing between charge and discharge through two relay and therefore i put the current monitor at the and of circuit but i made a mistake as shown.

How can I avoid this problem?

#### denci

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##### Re: Current monitor/sensor
« Reply #16 on: November 19, 2012, 11:12:34 AM »
Any idea??

#### denci

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##### Re: Current monitor/sensor
« Reply #17 on: January 21, 2013, 04:57:39 PM »
OK, I fixed the problem and i put the ZXCT1109 as shown in datasheet but i still have one problem.
If i want to get 0-5V output voltage and 0-10A sensing current i must put the Rsense of volue 10mE and Rgain 12,5kE, i get equations in datasheet.
But now i testnig the proper function of this measurments and i get 140mV in output with sense voltage 8,5mV and 410mV with sense voltage 16,4mV.
This is not what i want and not as calculated, it must be something wrong because i should get 0,5V in output with 1A (10mV sense voltage) current and so on, therefore 2A/V resolution??

#### denci

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##### Re: Current monitor/sensor
« Reply #18 on: January 23, 2013, 03:47:43 PM »
Any idea?

#### denci

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##### Re: Current monitor/sensor
« Reply #19 on: December 11, 2014, 12:04:55 PM »
I want to sense the current in my circuit (SLA battery tester) with current monitor IC ZXCT1109 but i have one question/issue:
Can i sense the current with Rload before the ZXCT or i need to use Rload as shown in datasheet?

Quote
I tried to sense current with this methode but i can't read any voltage on output pin
The IC is called and is shown as a high side current sensor but you connected it as a low side current sensor so of course it WILL NOT WORK!

Hi...a long time ago i asked a question about ZXCT placement in circuit and i started a project again and i will continue where i stayed, so i have one question.
In circuit below, which represent microcontroler (PWM) regulated discharge current/power with OP folower as we can see, where where shpuld i place the ZXCT1107 and shunt for measuring in circuit to ensure me relevant information about current??

#### audioguru

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##### Re: Current monitor/sensor
« Reply #20 on: December 11, 2014, 01:19:14 PM »
Your camera is horrible. Why don't you sketch the schematic using Microsoft Paint program or another program?

Your opamp has no power supply so it will not work. If it has only a single positive supply and ground then it must have inputs that have a common-mode voltage range that includes ground like an opamp in an LM358 dual opamp.

It looks like you are heating the load resistor by discharging the battery into it. The battery current also includes the base current of the PNP transistor.
Connect the sensing resistor for the ZXCT1107 between the positive terminal of the battery and the emitter of the PBZXCT110NP transistor.

#### denci

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##### Re: Current monitor/sensor
« Reply #21 on: December 11, 2014, 04:11:50 PM »
Sorry I took a picture quickly with phone and bad light i just want to show example where to put ZXCT because i did not get a reliable resault before at output pin of ZXCT.
I didn't draw a power supply but i have it off course, it is 24V and i took LM324 which have common-mode voltage range.
I took into account of base current of battery discharging also, this is the reason why i want to measure current via current monitor.
so i should put the ZXCT as mentioned, this is what made me confused.

#### denci

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##### Re: Current monitor/sensor
« Reply #22 on: January 18, 2015, 11:27:12 AM »
Your camera is horrible. Why don't you sketch the schematic using Microsoft Paint program or another program?

Your opamp has no power supply so it will not work. If it has only a single positive supply and ground then it must have inputs that have a common-mode voltage range that includes ground like an opamp in an LM358 dual opamp.

It looks like you are heating the load resistor by discharging the battery into it. The battery current also includes the base current of the PNP transistor.
Connect the sensing resistor for the ZXCT1107 between the positive terminal of the battery and the emitter of the PBZXCT110NP transistor.

Should i place shottky diode between transistor collector and load resistor for protection?
Voltage from OP folower feedback can occur also on transistor collector or no?

#### audioguru

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##### Re: Current monitor/sensor
« Reply #23 on: January 18, 2015, 12:49:35 PM »
Your circuit is missing a resistor from the collector of T2 to the base of the PNP output transistor to limit the base current. T2 will probably overheat without it.
The PNP output transistor is missing a resistor from its base to its emitter to help turn it off.
Both transistors add delay and additional voltage gain so the entire circuit will probably oscillate.

I think you should use a fast driver emitter-follower driving a fast power transistor emitter-follower since they have no voltage gain and their very small delay will not cause oscillation:

#### denci

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##### Re: Current monitor/sensor
« Reply #24 on: February 02, 2015, 01:10:32 PM »
i will thinking about my circuit and which material i have available for this project and maybe i should corrent my current circuit

i have onother PNP transistor and how should i connect each other in parallel to decrease dissipation of single transistor and therefore obtain less temperature on my heatsink, i think that it's quite same than with npn which must have emmiter resistor to equalize current through both transistor, it isn't?

#### audioguru

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##### Re: Current monitor/sensor
« Reply #25 on: February 02, 2015, 02:40:20 PM »
If you connect two transistors in parallel then each needs an emitter resistor so that they share the current fairly equally.
The opamp will probably not have enough output current to drive output transistors without adding a driver transistor.

I sketched a circuit with a PNP driver transistor and a PNP output transistor. They have enough current gain for the opamp to be able to drive.
BUT since they are both emitter-followers with a Vbe of about 0.7V and 1V then the output voltage will not go any lower than about +1.5V to 2V.

#### denci

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##### Re: Current monitor/sensor
« Reply #26 on: February 03, 2015, 01:39:22 AM »

Is this OK if we look back to my first version of circuit?
This is what I was thinking about and I think this is the most easy for correction my current version of circuit, I just want to add another transistor on my heat sink to decrease temperature on it.

#### audioguru

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##### Re: Current monitor/sensor
« Reply #27 on: February 03, 2015, 08:45:50 AM »
Your amplifier will oscillate because its transistors provide voltage gain. Then at a frequency where the opamp's phase shift would cause oscillation, its gain is less than 1 so it does not oscillate, but the total gain with the transistors is higher than 1 so the entire amplifier will oscillate when negative feedback is applied (the phase shift causes the negative feedback to become positive feedback at high frequencies).

Also, common emitter transistors have more phase shift than emitter-followers due to the Miller effect (the capacitance from collector to base is amplified).

Also, your PNP transistors are missing resistors that will turn them off quickly. So yours turn off slowly which adds additional phase shift.