Does anybody know IC for Amper meter?

[Shahriar]

Hi

I want to build a Digital Ampermetre upto 5A. Does anybody know an IC for this purpose.

ThanX in advance
Shahriar

[Guest Alun]

Just use a normal voltmeter IC with a current sense resistor.

[Shahriar]

Dear Alun

I am designing a high current Power Supply. If I put a resistor in series with PS and sense the dropped voltage across it, then I have increased the output resistor of my power supply. ???
the PS is a SMPS. I don't know whether I can calculate the current from some where else or not?

How does Ameter in digital Multimeters work. they can sense current down to 5uA or maybe less. do they use a Shunt resitor or do another trick?

ThanX in advance
Shahriar

[Guest Alun]

I am designing a high current Power Supply. If I put a resistor in series with PS and sense the dropped voltage across it, then I have increased the output resistor of my power supply. ???

You could use a hall affect sensor that monitors the magnetic field around the conductor if you don't want to increase the output resistance. Another way is to put the current sense resistor in before the voltage feed back loop of the regulator so the it'll compensate for the voltage drop lost in the resistor, you could mimimise the drop in the first place with a very low value resistor and use a mV meter and possibly a differential amp to.

Given I'd go for the hall effect sensor but it might be more expensive, anyway here's a diagram to illustrate my differential amp and current sense idea.

the PS is a SMPS. I don't know whether I can calculate the current from some where else or not?

You could do this in theory but you'll have to take the input into account and it could be complex.

How does Ameter in digital Multimeters work. they can sense current down to 5uA or maybe less. do they use a Shunt resitor or do another trick?

Current sense resistors are normally used for small currents under 10 amps and hall aaffects are used for large currents over 10A. Normal multi meters use current sense resistors but you can get clamp meters with hall affects to measure 100A or more.

[audioguru]

A TL071 or TL081 opamp can operate with its input voltages near its positive supply voltage.

[Ldanielrosa]

Allegro has hall effect current sensors for several ranges.

[chernobyl]

Could you send me he schematic of this thing? :)...please...

[Guest Alun]

A hall efect sensor is a module, you don't norrmaly need a schematic, you can buy hall effect sensors from RS componants and probably many other suppliers.

[ante]

Or, you can just omit the current sense resistor and use the wire if you don’t want the extra voltage drop. Alun’s circuit will work with only the wire as shunt resistor.  8)

[Guest Alun]

The problem with trying to measure too smaller voltages with this circuit is you'll need a very high gain, and the input offset voltages, both of these factors will increase the error well beyond and acceptable margin.

[ante]

Hi Alun,

If the wire is extremely short it might require a more delicate solution but it will work. I have used 30cm of a 50sq mm wire for measuring the current (0 – 500ADC) with no big problems. I also have had some issues with unreliable hall sensors in the same range of current! 8)