I'm constructing a boost converter, and I need to measure both the input current and the output current. Currents range anywhere from 25A to 200A, depending on the model. My controller is referenced to the negative rail of the converter. I've been focusing on hall effect sensors, but it occurs to me that I could use shunt resistors in the negative leg instead. What are the advantages and disadvantages of each approach?
I am not an expert in the field but I can try to help jotting down some quick ideas.
Hall effect sensor
- galvanic insulation between the measurement circuit and the circuit to be measured
- they can be placed anywhere on the current path (voltage is not a problem), thus easyness of installation and eventually servicing
- they nearly do not affect the measured current so they are great if this is a concern
- cost: a high current, precise sensor can cost tens of bucks
- bandwidth: the sensor and the sensed wire are coupled through a transformer, and of course it has its own frequecny response. A piece of copper (aka shunt resistor) is less affected by this problem.
- magnetic fields: an external fixed magnetic field can cause an offset in the measurement that must be somehow taken into account
small and cheap, I bet that with a good pcb manufacturer you can make your shunt resistor on the pcb paying only for the increased size, but keep in mind that the copper resistivity depends on temperature, moreover the pcb outer layers thickness is not precise while inner layers are somewhat better.
You can get cheap SMD shunt resistors down to 1m\$\Omega\$ from ohmite
- they can dissipate quite an amount of power, and a tradeoff exists between precision and dissipated power. They can get quite hot too.
- they do affect the measured circuit, namely there's a voltage drop across them and that might not be acceptable for very low voltage, high current applications. You can't measure the current consumed by an array of cores that are powered with 1.8V with a shunt that drops some 100mV
That is just what comes to me from the top of my mind, I'd be very happy to integrate/correct this list reflecting any reasonable comment from below.
The shunt isnt looking good on your high power job. If its to develop a reasonable voltage to allow some accuracy at the low end of your high current range ,then the worse case heat generated at max current will be bad,now if you use a gold plated opamp then you dont have your cost advantage and the better opamp working at lower input volts is more likely to get stung by the strong RF fields inside your SMPS .So the shunt is more likely to give hassles at prototyping.Now when you do a product range you can stuff more turns of thinner wire through to reduce your range.In other words one size hall device should fit all.there is one thing to watch out for with the hall and thats its tempco ,its small BUT it goes the wrong way which means that current will rise if it gets hot .It doesnt generate significant heat BUT what if your cable is small or its close to other hot components.
protected by Community♦ Aug 19 '14 at 17:55
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