question about step up booster DC/DC?

[horzonbluz]

inductorless booster

Hello, my friends.
I'm a newer to DC/DC, and i have very easy question about DC/DC.
What's the start up voltage of booster DC/DC?

 

[VVV]

I don't know if you are referring to a particular chip, but in general, the startup voltage is the minimum voltage at which the circuit will begin to operate (when the voltage is INCREASED from zero).
After the circuit begins to operate, you may, in most cases, reduce the input voltage below that value, and the circuit will continue to operate, due to built-in hysteresis, down to a lower voltage, the turn-off voltage or UVLO (under voltage lockout, if that feature is present).

 

[horzonbluz]

What's the input voltage that you have said?
Is it the power supply of the DC/DC circuits or other power supply?

 

[sunking]

it depond on you system. If the system is only one power supply, then the input voltage is it. But if there are two or more, most is the power supply which connect the output stage.

 

[VVV]

If you are referring to a chip only, then it is its supply voltage. If you are referring to the system, then it is the supply voltage of the entire system, such as the DC/DC.

 

[horzonbluz]

Ok! That's great help to me.
And i have an other question about the booster DC/DC.
What decide the load ability of booster DC/DC?
I test a booster DC/DC circuits. I let the power supply form 0v to 2V,
It works well when it has no load and the Vout voltage can step up.
But it does not work when i give it a 3.3K resistor load that the Vout voltage
can't step up. Why this happen?

 

[VVV]

First of all , what type of boost do you use? Inductor-based or inductorless?

This is a case of poor load regulation. It means the boost cannot source the required current. Please post more info, perhaps schematic, maybe I can offer some thoughts.

 

[horzonbluz]

My booster DC/DC is an Inductor-based step up DC/DC converter. It can work
from 0.9V start up voltage, output a 3.3V voltage and driver a 3.3K load.
When the Vin from 0V to 2.0V, the current has a max current 500mA, this is to say it need a power MOS that can source 500mA at least. But now it can't do that.
How to adapt the power MOS?

 

[VVV]

Something is terribly wrong with it, because the output current is only 1mA, so I cannot understand how the input current is 500mA at 2V, but the output sags at only 1mA.

Can you post the schematic or indicate which IC you use?

 

[Verba]

normaly DC/DC inductor based converters start up at 0.8-0.9V.
Start up circuit brings the output to 1.5-2V and then the control circ. is switched on.
In your case looks like your inductance is too large, try to decrease it and may be increace output capacitance