I don't have Multisim. Could you post a screen shot of the schematic?
help with multisim circuit
- 7th February 2012 06:48 PM #1lokeycmos
help with multisim circuit
so im trying to design a simple trickel charger for a 4.8v 7.95Ah NiMH battery pack powered by a wall wart. im shooting for 5v at about 200mA. im doing this on multisim first to work out any bugs. it doesnt seem to wanna work the way i want it. im using 2 LM317 regulators. one as an adjustable voltage regulator and the second as a current regulator.one thing i dont get is, the LM317 constant current is sposed to keep constant current at whatever load, but its not working that way. ive been playing around with different value pots and resistors. any help or advice is appreciated!
- 7th February 2012 07:51 PM #2ronv 0
- 7th February 2012 08:27 PM #3lokeycmos here ya go
Originally Posted by ronv 
0
- 7th February 2012 11:44 PM #4audioguru
The resistors in your LM317 voltage regulator are far too high. The resistor from the OUT pin to the ADJ pin should be 120 ohms and for the regulation to be 7.1V then the resistor to ground should be 560 ohms.
During charging, the current regulator regulates the current. When the battery is fully charged at about 5.6V then the input of the current regulator will be about 7.1V.
You have R1 completely destroying the current regulation so remove it.
Why is your input voltage (18V) much too high?
Where is the battery?
I don't think Multisim knows anything about an LM317 and neither do you.0Uncle $crooge
- 7th February 2012 11:56 PM #5lokeycmos I was doing lots of playing around with lots of different values of input voltages and resistors. this is just where i left off. thats why im asking for help. im using a variable resistor on the bottom right of the schematic as my "load" Originally Posted by audioguru 0
- 8th February 2012 12:52 AM #6audioguru Then I guess you did not look at the detailed datasheet for the LM317. It shows many examples for the more expensive LM117 that uses a 240 ohm resistor. The LM317 is less expensive and needs a 120 ohm resistor to keep the output voltage from rising (as told in the datasheet) without a 10mA load current. The calculations for the resistors are shown in the datasheet and are extremely simple so you do not need to "play around". Originally Posted by lokeycmos
Now your thread is on ANOTHER website. I won't bother with it.0Uncle $crooge
| Tags |
|
| Similar Threads | ||||
| Thread | Starter | Forum | Replies | Last Post |
| help with digital circuit | samcheetah | General Electronics Chat | 7 | 16th March 2004, 04:07 PM |
| Newbie help with reading circuit please | marchache | General Electronics Chat | 6 | 2nd March 2004, 07:27 AM |
| help with electronic circuit project | megavolt | Electronic Projects Design/Ideas/Reviews | 13 | 4th February 2004, 02:27 AM |
| Need some help with a circuit and don't know where to begin! | Zandor_Vorkov | Electronic Projects Design/Ideas/Reviews | 6 | 9th December 2003, 01:03 PM |
| Need help with relay circuit | rwroth | General Electronics Chat | 11 | 28th October 2003, 05:26 AM |