Hi,


i searched the forum for constant current circuits but didn't extactly found what i needed.

the circuit should operate as low as 1v (max 5v) and the output current 1ma.

Precision is important.

Current regulator diodes are a possibility (are the j505 recommended?) but a cheaper alternative would be great.


Thanks!

 

What about a J113 fet circuit?

 

Did you consider this type of circuit?
http://pdfserv.maximintegrated.com/en/an/AN4404.pdf

 

What is your supply voltage?
Does the load need to be grounded?

 

How precise does the current have to be?
The 1 volt minimum requirement is a tough one. The J505 needs as much as 2.1 volts to regulate.

Even the amazing LM10 op-amp/reference needs about 1.2 volts to operate... And the LM10 is little pricey at $2 to $3 each.

 

LM334, adjustable current source, max. out - 10 mA, input V - 2-20 V.

 

Thank you for all the suggestions so far!

I thought that the j505 worked as low as 1v (need to check the datasheet again)

isn't there current regulator diodes fit for this? (the gain of space is a big plus)

supply voltage 3v to 6v

precision is important but 1ma to 1.15ma is ok.

note that i test soil and water so the output/electrodes are submerged/buried.

 

the circuit should operate as low as 1v (max 5v) and the output current 1ma.

jfets would be a good choice here. Setting precise current output is tough with those guys, however.

 

See

 

Bordodynov,

This looks good, thank you! (isn't there an alternative for the 2sd2704k?)

I'll probably try this and also go for 2.5 - 3v with j505 (cheaper than the LM10).

 

alternative for the 2sd2704k (hfe=820-2700) is transistor with high gain (hfe>400). for example BC547C.
alternative BCV61C - DMMT5551, BCV62C -DMMT5401