# how to detect high current flow in circuits ?

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#### ringo888

##### Member level 1
current sensing

Evening Gents,

Can anyone explain to the how to detect high current flow in circuits, I believe a low value resistor is used? does anyone have any suggested circuit examples?

Regards,
Ringo888

#### betwixt

##### Super Moderator
Staff member
Re: current sensing

Resistor in series, voltmeter across resistor. Not worth a diagram.

Brian.

#### ark5230

current sensing

current I = V/R
using approximate ragne of expected current, select suitable low value of R to allow measurement of voltage across it with the instrument you plan to use.
Raoof

#### timof

Re: current sensing

ringo888 said:
Can anyone explain to the how to detect high current flow in circuits, I believe a low value resistor is used? does anyone have any suggested circuit examples?

Inserting a resistor with a small known resistance value is a simple solution, but it will lead to additional power loss.

Alternative solution, avoiding additional power dissipation, is to select two points in the metal routing, along the direction of the current flow, and measure a voltage difference between these two points. This voltage difference will be proportional to current. You can find the proportionality coefficient (i.e. effective resistance between these two points, corresponding to current density distribution for operating condition) either from test structures and measurements, or from simulation of the current flow in your metal interconnect system. Depending on the complexity of the metal layout, you can estimate the resistance between the two points analytically ("by hand"), or you might have to use a field solver in the case of complex layouts.

#### daltonvono

##### Newbie level 5
current sensing

For high currents, you can use a Hall Efect sensor. See www.alegromicro.com

#### kender

Re: current sensing

App notes on current sensing. https://www.diodes.com/_files/products_appnote_pdfs/zetex/an39.pdf
Here's a another interesting one about magnetoresistive sensors:https://www.diodes.com/_files/products_appnote_pdfs/zetex/an20.pdf. E.g. ZMC05 and ZMC20 current sensors.
Allegro Hall-effect sensors, which were already mentioned above: https://www.allegromicro.com/en/Products/Categories/Sensors/currentsensor.asp

What kind of current do you have:
- AC or DC? If AC, what's the frequency?
- Do you need to know instantaneous current? rms?
- Do you want to measure current, or just detect when it's above some threshold?
- What's your expected range of amps?
- What's the voltage at the point where you want to detect current?

### ringo888

Points: 2

#### ringo888

##### Member level 1
Re: current sensing

Thanks guys for your responses much appreciated, The app note links look very interesting.

Kender:
No there was no specific measurement just a general question, i'd ideally want to have a current sensing limit that would then switch a FET or BJT trans that would then go to a micro, something like anything greater than 1A. any suggestions on circuits?

Cheers Ringo888

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