Hello
I am trying to design boost converter with input 12v and output 24V,5A.I applied 50khz 50%duty cycle pan.but I did not obtained required output.Please check attached schematic and suggest me the solution.

 

What does "I did not obtained required output" mean exactly? It is not a very helpful description of the problem.

 

You need a recovery diode across C1,2 to capture the Negative pulse..

 

What does "I did not obtained required output" mean exactly? It is not a very helpful description of the problem.

Output voltage is 17V and input voltage drops to 5v from 12v.

 

input voltage drops to 5v from 12v.

You need a 12V supply with a higher current cpability.

 

You need a recovery diode across C1,2 to capture the Negative pulse..

What negative pulse?


Here's the schematic orientated properly.

 

Hello,

What are you using for the input voltage?
When you want 5 Amp on the output at double voltage, the input current will be at least the double of the output current.
I would expect an input current of about 12 Amps, adding some extra for the efficiency loss.

Bertus

 

What negative pulse?


Here's the schematic orientated properly.

View attachment 194727

From L1 left side, when Q1 turns off the right side will give a positive pulse through D1,and the left side will go negative, so it should have a recovery diode... Yes??

I'm sure you can prove it on the LT spice,
you wizzard.. ...

 

From L1 left side, when Q1 turns off the right side will give a positive pulse through D1,and the left side will go negative, so it should have a recovery diode... Yes??

Yes and no.
The left side will tend to go negative but is prevented from going significantly negative by C1 and C2 (assuming they are of sufficient capacity).

 

What size is the inductor? 40nH? 40uH? 40mH?

 

I'm constantly surprised by people that try to work with or get into electronics, *NEVER* understanding the relationship between current, voltage, and impedance as described by Ohm's law. People always seem to think that these 3 elements somehow operate independently of one another, and then when something does meet up, they can't understand why.

If input voltage drops, it's because load is drawing too much current. In this case, the boost converter itself is a load, and it is sacrificing voltage to try to make current (and it can't). Input does not have enough current.

Boost & buck converters must always be designed with an input voltage, output voltage, and load-current being supported consideration.

If you want to make your own boost converter, I recommend using the ubiquitous MC34063A.



The following component values (as referenced in the schematic above) will allow for input variation to 10.8VDC. It operates at 50kHz, 12VDC input, 24VDC output @ 5A. Since you're raising voltage, at a significant output current ability, you have to use a lot of current on the front end to achieve both:

cT: 455pF
Rsc: 0.0142 Ohms
Lmin: 5.102uH
cO: 51.161uF
R2: 18200 Ohms
R: 180 Ohms
R1: 1000 Ohms

Your peak input current (Ipk) will be 23.17A- make sure the Schottky can handle this. It will use 278.07W of power.

I've just done the math. It's possible some or all of the components, including the IC won't thermally handle that- check the datasheet to be sure.

 

WARNING: the very first calculation you should make when designing ANY DC-DC converter, or any DC-AC inverter is the power balance. In simple terms

POWER OUT will always be LESS THAN, POWER IN; sometimes it will be MUCH less than. Failure to heed this maxim is the road to electronic perdition.​

​

READ IT, KNOW IT, NEVER FORGET IT!!

Yes I know I'm yelling, but what choice do I have.

 

24V/5A is a bit beyond the ability of the MC34063. The step-up example in the data sheet only does 175 mA at 28V. 5A may be possible if you add an external power transistor. But that chip is an excellent starting point for playing with switching regulators; Motorola provided practical examples complete with PCB layouts that are ideal for making prototype boards using manual techniques. And the 34063 (or clones) can be found inside just about every old car cellphone charger.