short circuit current of boost converter

[mehmet1990]

Hi.
I must design a power inductor for a DC - DC boost converter and i have to learn the "max peak to peak short circuit current" of my converter to calculate the inductor size, air gap vs. But i cannot. What is exactly short circuit current in a boost converter and how can calculate it before design my circuit. If anyone can say a few words to help me i will be grateful. Thank you.

 

[crutschow]

The short circuit current needs to be limited by a current-limit circuit in the design. Otherwise the short circuit current is only limited by the impedance of the internal components and will likely go to damaging levels.

 

[dougy83]

The basic boost converter (shown below) doesn't effectively limit the current if the output voltage is less than the input voltage (which includes the output short-circuited).

The short-circuit current can be estimated using the following equation.

 

[MrAl]

Hi,

That's a good point, where if the switch stays open the current is just the current through the inductor diode and load.

But it really depends on the topology, because in one case it can go the other way where the switch is on all the time so there is no output current and all the current goes through the inductor to ground. That's because a basic boost would try to increase the switch 'on' time in order to satisfy the output voltage requirement which would be near zero with a shorted output. In fact, once the resistance on the output gets too low the basic converter would actually lower the voltage more and more because it would end up on the far end of the switching period which means there is never enough time to discharge the inductor enough to raise the output voltage.
In this case the output current would be low but the input current would be extremely high. So really in order ot make a good estimate we'd have to see the entire design. Of course if there was current limit built into the circuit that's even better.

 

[ronsimpson]

Mehmat1990,
Can you send a schematic of you circuit?
I need to know: input voltage, output voltage, inductance, switching frequency, output current, etc
I probably can determine at what current level the PWM will give up voltage regulating.