I need help!!!! (Designing a power supply)

power supply tip142 -amplifier

Hi, first time poster here.

I'm after some ideas or known circuits that would be capable of providing 7-8v @ ~15A from a 12v SLA Battery.

It's for a project for my rc car, i want to drive the rotostart for the engine from a 12v battery contained in a pit box.

I've measured the amperage of the motor in the rotostart at the specs are approx.

Start current = 8A
Continious current = 4-5A
Stall/Slow down current = ~15A

Thanks in advance for any help or guidance i've been on google for days looking for inspiration...

Cheers

James

psu lt1083

Dear,

At first step i can suggest this:

Use a high current linear Regulator ---> LT1083 7.5A + A high current Transistor

for Current Boost.(for examples : TIPxxx Series)

second solution is a switching regulator,but i can't suggest any regulator now.

third is use a compact DC-DC Converter BOX. For some examples goto

Phoenix Contact Website,They have attractive products.(www.phoenixcontact.com)

Good Luck.

Hi

Thanks for you help memarian.

Just need a bit more now if anyone can help.

I can get hold of the LT1085 and the TIP142 (Is this suitable).

If possible would someone be able to provide a basic circuit i can then expand on. Mainly the basic layout for these two components above and any more that may be needed to get some sort of working circuit.

Thanks for your help so far

James

Dear,

this a sample schematic for a linear regulator.

The voltage across R1 Turn on Q1 B-E junction and Transistor Turned on.

For calculation of R1 Resistor,When you want to turn on Q1,(at desired Regulator current)

you should calculate according the equation,For example if maximum current of regulator is 3A,and
you want to turn on Q1 @ 2.5 A,and after that Q1 provide current,

Veb(on)=2.5A*R1,if Veb(on)=1.4(for usuall Darlington transistors)-->R=1.4/2.5

and R=0.56ohms.

at this configuration,the Power dissipation is most important factor and it is:

Pdiss(total)=(Vout-Vin)*(Imax-Ireg(Q1-on))+Ireg(Q1-on)*(Vout-Vin)+R1*(Ireg(Q1-on))^2

In this Equation the First term is For T1,Second is for U1 and third is for R1.

At this state you must have a good heatsink.

TIP142 is a NPN Transistor,For this Config you need a PNP(Darlington is better)

Transistor.

Good Luck.

Dear,

PNP high current Darlington transistor:

TIP135,TIP136,TIP137 : 12A(peak),8A(CW),70W(max),first 60v,second 80v,third 100v

MJ4030,MJ4031,MJ4032 : 20A(Peak),16A(CW),150W,1st 60v,2nd 80v,3rd 100v

about my previous post : Be Careful about PNP Darlingtons,some PNP darlingtons

needs Veb upto 2~3 Volts to turn on.

Good Luck

Dear,

See this Link (Linear Technologoly High Current Switching Regulators):

https://www.linear.com/pc/viewCategory.do?navId=H0,C1,C1003,C1042,C1032,C1092

They have Regulators up to 20A and more.(Such as LTC1775,LT3800) but their circuits are more complex than a linear regulator.

Good Luck.

Thanks very much for your help memarian.

This is exactally the information i needed, and more.

I'll post on here what i get done.

Thanks again

A very happy James