uCurrent max current limitation doesn't seem correct

[thereza]

Hi!

I recently ordered a uCurrent (i just wasted a day debugging a problem that went away when I unplugged my HP 34401A (for a current measurement)).  However, I want to measure currents up to 1A and the specifications only go to 300mA for the device. 

In looking over the circuit, you should be able to measure +- 1.5A (limited by the max output voltage of U1, which claims to be rail to rail, so 1.5V).   I was wondering where the 300mA limit comes from?  at 1.5A, i calculate a power dissipation of .03W which R1 should tolerate..

I was also wondering if you could comment on the need for R12/R9 -- I assume they are for protection, but not sure of what...

Thanks!
Reza

p.s. the photo capcha sucks on this site. 

[EEVblog]

The Captcha goes away after a couple of posts.

The current limit is the contact rating for the switch.
R9/R10 are for potential stability with capacitive loads and some protection - just in case.

[thereza]

thanks for the prompt reply.  So I can short SW1 with some jumpers to increase the current capability (and lock it in mA mode) and get 1.5A through it?  Too bad you didn't use a higher load-capable switch in the design. 

Thanks!
Reza

p.s. i keep failing the capcha.   the g looks like a 9

[eevblogfan]

hey

why don't you use logick gate fets and use the same switch so you can use it for all ranges ?

p.s: you already got micro volt resolution cepable multimeter , why don't you just use simple shunt resistor ?