Adjustable Constant Current Source

[bjwong]

Hi.

I'm designing and implementing a NiCAD battery charger for fun. So far, I have my LM317 outputting approximately 1.2 A in a constant current source configuration. My question is how do I modify it to be an adjustable constant current source (say through my microcontroller) so that once the batteries' voltage plateaus then I start trickle charging and not damage my batteries? Thanks.

 

[bjwong]

I realized that I haven't attached a circuit schematic. The circuit I used it the constant current source straight from the LM317 datasheet. I'm leaving this open for interpretation; hopefully, we'll see some interesting circuits .

 

[IRstuff]

The 5A constant current source shown in the National LM317 datasheet already has an adjustment for current

TTFN

 

[bjwong]

The schematic shows the current to be adjusted through a potentiometer. I wish to adjust the current by way of microcontroller (for example through a DAC).

 

[IRstuff]

Just replace the potentiometer with a digital pot

TTFN

 

[electricuwe]

Do not make things more difficult than they are !

Use a circuit for voltage regulator (voltage set for trickle charging) with current limit (current limit set to desired charge current).

If you want a more sophisticated charging algorithm try to find special ICs, some containing even a microcontroller, designed for that purpose.

 

[cbarn24050]

Hi, you should not trickle charge nicads, once they are charged turn the charger OFF.

 

[callicospfx]

The DAC will work and so will an ADC to monitor your circuit. Yeah, it's pretty complicated for an LM circuit but if it's for fun, then have at it!

DC


Doug Calli
Callico Special Effects