steev Posted February 28, 2006 Report Share Posted February 28, 2006 hello alliam trying to design a voltage regulator ckt which gives output of 3V and 500-700ma of output current.input is from a led-acid battery rated as 12v-2.5Ahon net i found below circuit which is for battery charger.circuit no-4http://agendawiki.com/cgi-bin/aw.pl?ChargingCircuitsbut regrading this voltage regulation some one saidThe biggest problem I see is that the efficiency of such a scheme would be terrible. Assuming the full 700ma of current drawn from the battery, the linear regulator would dissipate 6.3 watts while only 2.1 watts would go into the 3 volt load. The overall efficiency would only be 25%. A switching regulator would give you more like 85% efficiency. There are lots of switching regulator designs posted with 3v and 3.3v outputs.and he shown me this linkhttp://www.rowan.sensation.net.au/electronics/stepdown.htmland another one suggested L200 based voltage regulator.iam really confused between these.can u help me. Quote Link to comment Share on other sites More sharing options...
ante Posted February 28, 2006 Report Share Posted February 28, 2006 Hi steev,This is definitely a switch regulator application. I think you should go for the MAX 724 / 726 that is simple and reliable. With only a few external parts, high efficiency and low quiescent current it’s a good choice. Quote Link to comment Share on other sites More sharing options...
steev Posted March 2, 2006 Author Report Share Posted March 2, 2006 thanks anteiam also planning to design switching regulator only.but most them are using inductors.is there any inductorless regulator.(as i want to keep it as simple as possible)and i am unable to find schematic for MAX724iam new to these circuits.can u help me with the circuit diagram.(i need to control (lead acid battery)12v 2.5amp to 3v 200-500mah)thanks once againsteev Quote Link to comment Share on other sites More sharing options...
ante Posted March 2, 2006 Report Share Posted March 2, 2006 Hi steev,http://pdfserv.maxim-ic.com/en/ds/MAX724-MAX726.pdfOn the first page of this data sheet you will find a circuit “Typical Operating Circuit”, you need to change the resistor values of the two resistors in the voltage divider to get the desired output voltage.If you can’t find the MAX724 perhaps you could get the LT1074 that is almost identical. Here : http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1033,P1005The circuit you see here is very simple and I can’t see why a small inductor would be a problem. ;) Quote Link to comment Share on other sites More sharing options...
steev Posted March 2, 2006 Author Report Share Posted March 2, 2006 thanks ante ur too good man.one more help i needed here.iam connecting this power supply (3v 200ma from a 12v 2.5A lead acid battery) to a RF transmitter.is it okimean as this circuit uses inductor this might effect the RF.so what is ur openion.is it ok to go with MAX724 or LT1074or linear type regulators imean lm317,L200 etc Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 3, 2006 Report Share Posted March 3, 2006 A 3V transmitter won't draw much more than only 20mA, an FM stereo one about 30mA. Use an LM317 linear regulator. Quote Link to comment Share on other sites More sharing options...
steev Posted March 3, 2006 Author Report Share Posted March 3, 2006 then how can i limit the current if i use lm317 regulator.as the source current is 2.5amp and transmitter draws 20-30ma(as u said).i think current shld be limited or else it might destroy my small transmitter.2.5amp to 30ma Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 3, 2006 Report Share Posted March 3, 2006 Steev,An electronic circuit takes only as much current as it needs. The transmitter won't draw more than 20-30mA unless you short its power supply wires.Your battery is probably rated for 2.5A/Hrs, not just 2.5A. So it can probably provide 25A for a few minutes to a short or very low resistance. Quote Link to comment Share on other sites More sharing options...
y01jpowell Posted March 3, 2006 Report Share Posted March 3, 2006 NO ;D :D >:( :o ??? ::) Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 3, 2006 Report Share Posted March 3, 2006 NO ;D :D >:( :o ??? ::)No what?The battery is a lead-acid type that has an extremely low internal resistance, so it can supply many amps of current to a short or very low resistance.The transmitter operates from only 3V so its current is very low. If the transmitter operated from 100V or more then its current would be much higher. Quote Link to comment Share on other sites More sharing options...
steev Posted March 3, 2006 Author Report Share Posted March 3, 2006 thanks audio gurui got it.it takes exactly the amount needed.so i'll try lm317(as amount of current used is very low.i hope chip will stay coll.but i'll still use a heatsink)on more thing abt the step down dc-dc converter.it uses(most of them) inductors.so u think this cause any effect on the circuit we r connecting at the output.imean if the output is to a fm transmitter.... Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 4, 2006 Report Share Posted March 4, 2006 so i'll try lm317(as amount of current used is very low.i hope chip will stay coll.but i'll still use a heatsink)An LM317 won't get warm powering a 3V transmitter from 12V.Please post the schematic of the transmitter. What are you going to use it for? Have you tried it?the step down dc-dc converter.it uses(most of them) inductors.so u think this cause any effect on the circuit we r connecting at the output.imean Quote Link to comment Share on other sites More sharing options...
steev Posted March 4, 2006 Author Report Share Posted March 4, 2006 this looks ok to me.i'll replace R1 and R2 with 120,18Ohms resistors.(no VR1).then i think i'll get 3v output.what wattage do i need for those resistors?The LM317 is a linear voltage regulator. It is not a switching DC to DC converter.yes i know that.iam talking abt those maxim dc-dc converter chips. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 4, 2006 Report Share Posted March 4, 2006 The resistors in the LM317 circuit have hardly any current in them so their power is also very low. I think a 3V LM317 circuit should be like this: Quote Link to comment Share on other sites More sharing options...
steev Posted March 4, 2006 Author Report Share Posted March 4, 2006 thanks for the schematic.do this ckt need any overvoltage protection.imean diode across the output. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 4, 2006 Report Share Posted March 4, 2006 Your transmitter isn't going to be a generator so the LM317 doesn't need a protection diode. Quote Link to comment Share on other sites More sharing options...
steev Posted March 4, 2006 Author Report Share Posted March 4, 2006 thanks audio guru and ANTE.u both helped me a lot thanks once again. :)i don't want to start another thread for my friends quiry.so iam posting here only.i hope u will solve his problem also.he is working on a ckt which drives 6 LED remotely.imean using a RF transmitter(35Mz) and receiver.function is like when transmitter pressed on 6 LED's mounted on receiver side will glow.receiver uses 3AA cells and transmitter 2AA.he connected 6 LED's in paraller.so as voltage is above 3v.they r glowing with enough brightness.now the thing is they consuming power(current) quickly.so he want to know is it possible to boost current like voltage using some charge pumps.so that the LED's can be driven for long time.i'll be waiting for u r repliesthanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 4, 2006 Report Share Posted March 4, 2006 Each LED might draw 20mA to 25mA. Therefore 6 will draw up to 150mA which is a lot of current for AA cells. The current would be less if the LEDs were in series or if they are blinking like in my Ultra-bright Chaser projects. Quote Link to comment Share on other sites More sharing options...
steev Posted March 5, 2006 Author Report Share Posted March 5, 2006 series means more voltage.thats why we choosed parallel connection.so is it possible to boost current? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 5, 2006 Report Share Posted March 5, 2006 series means more voltage.thats why we choosed parallel connection.so is it possible to boost current?Use bigger battery cells, C or D cells instead of little AA cells. Quote Link to comment Share on other sites More sharing options...
steev Posted March 5, 2006 Author Report Share Posted March 5, 2006 i got some max 660 chips (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1140)so can we use this chip to make the circuit work for long times.like http://www.mitedu.freeserve.co.uk/Circuits/Misc/ledtorch.htm Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 5, 2006 Report Share Posted March 5, 2006 The MAX660 is a high current voltage doubler.With a brand new 3V battery powering three 3.6V white LEDs through the three 1N4148 diodes, the light will be extremely bright and the battery's current will be very high for a few minutes if the LEDs don't fail due to over-current. Then the brightness will decrease as the battery voltage runs down since the MAX660 doesn't have a voltage regulator.The circuit doesn't save any current. The battery won't last long. Quote Link to comment Share on other sites More sharing options...
steev Posted March 5, 2006 Author Report Share Posted March 5, 2006 u said some thing abt flasher.will it saves current.while searching for a max600 based flasher i found thishttp://www.laserfaq.org/sam/samschem.htm#schmsc5bwhat do u say abt it.and pls post ur flasher schematic too.thanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 5, 2006 Report Share Posted March 5, 2006 Why do you need 6 LEDs?A single ultra-bright white, blue or green LED will shine down the street or across the street at night.If you reduce the current then the battery will last a long time but the light won't be bright.You can use a Cmos gate IC to make a fast oscillator to blink an LED and a slow oscillator to make a long pause in the blinking. The Cmos gates can drive a transistor to give plenty of current to the LED for it to be bright, and since it doesn't draw current when it is between blinks then the battery lasts a long time. Quote Link to comment Share on other sites More sharing options...
steev Posted March 8, 2006 Author Report Share Posted March 8, 2006 hi againwe can't use more voltage here as the receiver is rated at 3.6v only.so we decided to go with parallel connection(we found a good high current battery pack).so can u show me a circuit which can flash 5(we decreased the number) LED's with appx. 0.5sec timing gap.and one more thing is size of circuit.we almost ran out of space.so pls show us some small circuit. Quote Link to comment Share on other sites More sharing options...
login
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.