i have toroidal inductor and i want to use it in dc-dc buck converter but i don't know its value , how to measure it ?
what would happen if i use this coil schaffner RB series 3 mhhttp://sa.rsdelivers.com/product/sch...h/7690578.aspx in 17-9 volt buck converter 55 watt ? will it be ok or should i use smaller inductance ? also could i use any type of inductors or just toroidal coil ferrite core?
how to calculate the inductance needed for buck converter?

 

You can measure the inductance by applying a pulse of DC and measuring the rate the current increases with time (by measuring the voltage across a small resistor in series with the inductor). This requires an oscilloscope for the measurement.

The amount of inductance you need depends upon the particular converter configuration you choose. That data sheet for the buck converter controller you want to use will tell you how to calculate the inductance required.

The inductor doesn't have to be toroidal but it should have a high frequency core such as ferrite.

 

would you propose a company to buy from it ?

 

Coilcraft is one that has a large assortment of inductors.

 

would you propose a company to buy from it ?

Pulse Engineering makes great inductors for SMPS

 

toroidal inductor isn't available in my area is there any other type could be used ?

 

toroidal inductor isn't available in my area is there any other type could be used ?

To help resolve this guessing game, what type of inductors are available in your area?

What is your area?

 

What is your area?

EGYPT is my area

 

EGYPT is my area

That wasn't my question -- What type of inductors are available in your area? What suppliers are available to you?

 

finally i found this coilhttp://www.digikey.com/product-detail/en/PE-92108KNL/553-1553-ND/2266125 but i need 500 uH ,100KhZ ,7Amp . i couldn't find any other suppliers

 

Your inductance value seems to be too high for your requirements. Here's an inductor calculator you can use.

 

these are my requirements and i think it is normal , the output of the calculator was close to the value i bought 100uh .my
input power is 55watt if i set v out to 9 volt and load current 3.6 amp to suite the inductor i bought the output power will be 3.6*9=32.4 watt however input power was55 w so did i miss any thing, i think that i should modify the current to be 7 amp consequently i will parallel to inductors

 

these are my requirements and i think it is normal , the output of the calculator was close to the value i bought 100uh .my
input power is 55watt if i set v out to 9 volt and load current 3.6 amp to suite the inductor i bought the output power will be 3.6*9=32.4 watt however input power was55 w so did i miss any thing, i think that i should modify the current to be 7 amp consequently i will parallel to inductors

In post #10 you said 500μH so that's why I questioned the value.

Here's a 7A 100μH inductor.

 

I want to make it suits my toroidal 100uH,3.6A could i do that or i won't feel difference in output as input will be 3A,17V

 

It's the output current, not the input current that determines the required current rating of the inductor.

 

so i could use this toroidal to get 3.6 Amp and the output voltage should be 55/3.6=15.2 as 7A is not available.

 

i used the attached circuit with atmega 8 to drive dc buck converter and it was working very well , then i increased the input voltage on the drain to 20v and the input current was 4 A (from a power supply ) suddenly the output on Ho of IR2112 was zero when i removed the converter the output on Ho was 7.6 v dc constant when the volt on drain Vd was 9.6 . and when i connected power resistor to the source of the mosfet Ho was zero ,did i lost the driver ?
also I noticed that when I increased Vd to 20 volt the output on IR2112( Ho) increased too ,the pwm was amplified to 25 v on the Mosfet gate how could the IRfz48 mosfet survive while Vgs from (10-20 v )?

 

Since there is not inductor in the circuit I assume this is just a test of the switch(?). What is the value of R5?

Sounds like you may have lost the driver, but I don't see why it would have failed.

The transistor gate to ground voltage will be high but the bootstrap voltage between the transistor gate and source is less (which is the critical voltage).

 

there was inductor when the driver was working then it stopped so i simplified the circuit to know what happened . R5 is ranging from 4 to 10 ohm i don't remember exactly its value when i raised the input voltage to 20 V , i don't know why does the voltage on Ho raised when i raised the drain voltage . i guess that the driver has been damaged but why ??

 

Was there a free-wheeling diode from the MOSFET inductor interface to ground. I don't see such a diode in your circuit. Without that there can be high voltages induced into the circuitry.