Help needed on boost converter circuit

[masa]

Hi, newb here and need help on a DC-DC boost converter circuit
The input is a varying 11v-14v and I need a regulated 16v to 18
output
The switching frequency isn't critical, but the pulsed output curren
needs to handle a peak of 15A

Can anyone suggest a suitable IC and perhaps provide some insight int
a workable circuit

thanks

 

[martin griffith]

On Sat, 17 Sep 2005 11:36:02 -0500, in sci.electronics.design

Hi, newb here and need help on a DC-DC boost converter circuit.
The input is a varying 11v-14v and I need a regulated 16v to 18v
output.
The switching frequency isn't critical, but the pulsed output current
needs to handle a peak of 15A.

Can anyone suggest a suitable IC and perhaps provide some insight into
a workable circuit?

thanks!

LTspice free from www.linear.com suggests LT1270A


martin

 

[martin griffith]

LTspice free from www.linear.com suggests LT1270A


martin

ooops, misread 15 A for 5A
sorry


martin

 

[Joerg]

Hello Masa,

Hi, newb here and need help on a DC-DC boost converter circuit.
The input is a varying 11v-14v and I need a regulated 16v to 18v
output.
The switching frequency isn't critical, but the pulsed output current
needs to handle a peak of 15A.

Can anyone suggest a suitable IC and perhaps provide some insight into
a workable circuit?

Many chips state a limit of 10A, for example the LM3478. But since you
only have to add 7V (or slightly above 100W) worst case you could ask
National whether it'll work. IIRC the main reason why they place such
limits is the gate capacitance of the FET it has to drive.

Else, look at the former Unitrode UC chips. Now at TI and there are some
excellent application notes, almost cookbook style.

Regards, Joerg

 

[Ken Smith]

Hi, newb here and need help on a DC-DC boost converter circuit.
The input is a varying 11v-14v and I need a regulated 16v to 18v
output.
The switching frequency isn't critical, but the pulsed output current
needs to handle a peak of 15A.

Can anyone suggest a suitable IC and perhaps provide some insight into
a workable circuit?

How long are the pulses on the output? Can you use a large capacitor to
handle them so that the regulator only needs to provide the average
current?

At these currents, you may be better off with a PWM chip and power MOSFET.
Although it is more parts, it allows you to keep the 15A currents away
from the ground of the PWM chip.

Go get a copy of switcher cad from Linears web site. It is very helpful
for checking out your design before you commit it to real parts.

You need to perform some calculations:

We are boosting 11V to 18V so the inductor has 11V on it during the on
time and 7V during the off time.

For the smallest inductor, you want the current in the inductor to just
stop before the switch turns on again. This means that the peak
current must be:

Ip = 2 * 15A * (Ton + Toff)/Toff

But:

Ton = Toff * 11V / 7V

So:

Ip = 30A * (Toff * 11/7 + Toff)/Toff

Ip = 30A * 18/7 = 77A


This is likely to be the biggest problem in the whole design. You need an
inductor that is good for a fair bit more than 77A and is also good at the
switching frequency. I'd look for this from www.rencousa.com or
www.coilcraft.com.

 

[kell]

Hi, newb here and need help on a DC-DC boost converter circuit.
The input is a varying 11v-14v and I need a regulated 16v to 18v
output.
The switching frequency isn't critical, but the pulsed output current
needs to handle a peak of 15A.

Can anyone suggest a suitable IC and perhaps provide some insight into
a workable circuit?

thanks!

11 to 14 volts... Sounds like you're putting this thing in a car.
I would suggest, instead of pulling 270 watts through a switcher, take
power directly from the car battery (if that's what it is) and build a
switcher with an isolated output to provide the extra 7 volts you need.
Use the switcher's output in series with the battery.
That way you only have to build a 105 watt switcher instead of a 270
watt switcher.
If it was me I'd use the SG3525 chip. Drive a transformer with a
center-tapped primary in push-pull. The data sheet for that chip kind
of s***ks, though. You might find example circuits by going to
www.fieldlines.com and doing a search. Don't forget to ground pin 10!

 

[masa]

Thanks for all the advice and links everyone
Kell, yes this is going into a car - it will boost the voltage goin
to the coils to say 16v regulated instead of the fluctuating 12v
I'll look into the suggestions and see what I can find
thank

 

[Rich Grise]

Thanks for all the advice and links everyone!
Kell, yes this is going into a car - it will boost the voltage going
to the coils to say 16v regulated instead of the fluctuating 12v.
I'll look into the suggestions and see what I can find.

By "coils", do you mean "ignition coils" or "spark coils"? If so,
then it sounds like all that you're looking for is a spark booster
of some kind, in which case this is almost exactly the wrong
approach.

I'd seriously suggest looking up a local performance shop and
ask them what they'd recommend for a hotter spark.

Good Luck!
Rich

 

[JeffM]

it sounds like all that you're looking for is a spark booster

...in which case this is almost exactly the wrong approach.
I'd seriously suggest looking up a local performance shop
and ask them what they'd recommend for a hotter spark.
Rich Grise

Yup.
http://www.google.com/search?q=capacitive-discharge-ignition