24V to 12V about 8-10amps converter

[Wizpic]

I Have looked around and not found much information what I'm looking for, I've seen plenty of 12V to 24V versions though

I'm after a schematic or info to build one, I need to drop 24V input (29V max) to 12V(13.8V to allow for volt drop) about 8-10amps output

What would be the best way to do it, It must also be robust desgin

any ideas ?

wizpic

[pickit2]

I would look at any 12v bench power supply and build from the smoothing caps on, C1 pwrsup.gif,
C1 could be lower value say 470uF if from DC power. you could power U1 via diode from + of C1.
You could also remove Q4 and Q5 and resistors R11,12,15,16 as you only need 10Amp.

http://www.elecfree.com/electronic/138v-25amp-power-supply-with-lm7232n6776/

[Wizpic]

I did think of doing that way but this may become a comercial product, If I can sort it out well I say comercial product I'm only designing it hopefully

I'm just seeing if I could do it and try it

[DTiziano]

I think that a buck switching power supply is a must for this application.
Did you check the Linear technology application notes?
You may found some interesting ideas.
At pag. 30 of the linked document, there is a switching preregulator followed by a linear one.
Not efficient as a classical switching but has lower noise.
But there are many other solutions.

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1021,P1222,D4123

[Wizpic]

I've had a quick look through that can't see 24v to 12v but I shall read through more in depth but it has give me some ideas how it can be achieved I persume that the V out and the V in can be altered by changing the values, I shall have to pick a desing and down load the data sheet for that chip

[sohel]

hola. sir.

I know u r most senior member (also with my respect). if u dont mind i will help u

 r u talking about smps, battery charger, constant v/a? which topology u want digital or analog pwm with feedback.

[Wizpic]

I want to drop a 24-28V input to 13.8V ouput around about 8-10amps, This will be used in short busrts and all day, It may be inuse for 2 minuutes then nothing for 5 minutes then again for 2 minutues, it would be like this all day for 8-10hrs

I suppose it it a SMPS, I was thinking of using a pic chip to control it or in some way, I will be using a PIc to detect the voltage in and out and shut it found if to much voltage/current is found also use it for an usto switch system between 12 and 24V system

I shal be able to take care of the second part when I did a serach i was calling it a converter found a bit more out when I put a buck step down conveter, Any advise or help would help 

Thanks for your respect, I would be grateful for your help

[tAhm1D]

Hi,
Please find herewith an easy but efficient smps circuit, which I think will fulfill the  most senior member's requirement. I used the circuit and it is very reliable. All the required data is provided as attachment. For tailor made control purpose, one can use  Micro controller along with this circuit.

[Wizpic]

That's a great article and I shall enjoy reading trhough it,  hopefully this should do the trcik

I'm off to source the parts and get PCB made

[tAhm1D]

I think that a buck switching power supply is a must for this application.
Did you check the Linear technology application notes?
You may found some interesting ideas.
At pag. 30 of the linked document, there is a switching preregulator followed by a linear one.
Not efficient as a classical switching but has lower noise.
But there are many other solutions.

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1021,P1222,D4123

Hi DTiziano,
The AN of Linear Tech is very thought provoking and useful. But,for practical application, one should be very careful. In page 30 of the AN, the mentioned Linear regulator LT1083 is of 7.5A max and LT350A is of 3A capacity which will not fulfill the 10A requirement. One more thing in choosing the Linear Regulators- They are inefficient as the efficiency is very low and so they dissipate huge heat and hence large heatsink is required. It is preferable to use total smps for better efficiency.

[suzuki]

Sir,
Please have a look at this link, 3-24V in,peak efficiency 95%,output voltage 0.8v to 80% Vin, 8A output current.

http://www.fairchildsemi.com/ds/FA/FAN2108.pdf

Regards

[tAhm1D]

Hi suzuki,
I found the link is interesting and downloaded the Fan2108 datasheet. The ic seems to be very useful but it is SMDtype,which is not possible to use on my part. Do you have any idea whether it is available in DIP package? If it is available in DIP package, it can be conveniently use in low power Battery Charging.

[kayvee]

It does look an interesting part indeed.  I would doubt, however, that it is available as a leaded part, as the thermal bond pads on the underside of the packaging would be required for the part to function as designed.

[Walkura]

Good evening Wizpic .

I wanted to show you a few datasheets concerning pic-based buck inverters .
Although they are for driving leds or chargers it might be a starting point .
Further i would like to advice the books of Pressman and Marty Brown .
With combining the datasheets and the formula's from those books your almost there .
(except for the dirty hands and cold sweat)
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en012124
http://www.microchip.com/Stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en027652
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en025786
The books i uploaded on rapidshare and are in the following post .
http://www.sonsivri.com/forum/index.php?topic=12417.0
When you have a bit closer look at the datasheets and then compare it to lets say a 384*(3844 or 3840)or any other "current mode pwm controller"  its basicly the same game .
Personaly i prefer external mosfet ,when i make mistakes its easy and cheap to replace
When you want it to be in Pic processor its in itself no problem ,as you could see the setup and regulation is almost identical .
Just make the pic to generate the pwm according to the feedback and in the books you can find all calculations you need for the inductor & mosfets needed .
Have fun and be carefull .

Good luck .

[Wizpic]

Some great links there Walkura, I shal beare your thoughts in mind , I shall do some more reserach

Walkura you will have to drop me a e-mail I lost yours

nice to hear from you

wizpic

[sohel]

please download from microchip, it will handy for u.

Switch Mode Power Supply (SMPS) Topologies (Part I) (AN1114)

Switch Mode Power Supply (SMPS) Topologies (Part II) (AN1207)