meaning of L680 in LM2576

[furqankaimkhani]

There is mention of the L680 inductor in the LM2576 datasheet. Figure 3 on page 9 of (http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS011476.PDF).

While in a diagram, they show 100uH inductor. Its mentioned that this L680 mean 680uH. Can anyone pls put light on need of this induxtor here. What if i dont use inductor here?

 

[FoxyRick]

The chart is showing you the maximum input voltage vs. maximum load current curves for each of a range of inductances. Paragraph 1 on page 8 details how to use your maximum voltage and current to choose the inductor value from that chart. Plot your max V and max I on the chart, and the inductance is shown in the region between the lines.

You must choose an appropriate inductor for your situation. The use a 100µH inductor in the circuit diagrams is just an example.

What if i dont use inductor here?

You must, it's a switching regulator. It uses the inductor to store portions of energy in its magnetic field, and then releases the energy into the output capacitor. By controlling how much energy is allowed into the inductor (by controlling the switching), the device can regulate the voltage.

 

[manishanand14]

Hello furqankaimkhani !

While in a diagram, they show 100uH inductor. Its mentioned that this L680 mean 680uH. Can anyone pls put light on need of this inductor here. What if i dont use inductor here?

LT2576 has a 52 kHz fixed frequency internal oscillator.

Inductor used is a part of LC low pass filter.
The circuit will work without a filter but with very high ripple content which is undesirable.

 

[FoxyRick]

manishanand14, you are giving bad advice.

The circuit will not operate correctly without an inductor, it is designed to use an inductor.
The inductor value is not fixed by the oscillator frequency.
The inductor value must be changed according to the chart, as the datasheet itself says!

 

[maxseeley]

Hello furqankaimkhani !



LT2576 has a 52 kHz fixed frequency internal oscillator.

Inductor used is a part of LC low pass filter.
The circuit will work without a filter but with very high ripple content which is undesirable.
Also the value of inductor depends upon the internal oscillator frequency which is 52KHz.
So better don't change the inductor value as a filter circuit design depends entirely on the frequency of operation.

This circuit would not function without an inductor.

The internal oscillator frequency is one variable that determines the characteristics of the inductor - the others being Vin, Vout, and Iout.

 

[manishanand14]

Hello Friends!

If I am wrong please correct me.

The circuit will not operate correctly without an inductor, it is designed to use an inductor.

I think the circuit will work with bad performance as ripple content will be very high.Also what I know is ,that a buck converter can work without a filter circuit with compromised performance.

The inductor value is not fixed by the oscillator frequency.
The inductor value must be changed according to the chart, as the datasheet itself says!

Also can you please explain me the reason for this.

 

[FoxyRick]

If I am wrong please correct me.

I just did ;-)

I think the circuit will work with bad performance as ripple content will be very high.

The chip regulates the output by feedback - how will it cope if the inductor is not present and the feedback is an erratic, switching waveform? It won't cope. It's not simply a case of having high ripple. It might max out, it might shut down, it will not operate correctly.

Also can you please explain me the reason for this.

I suggest you read the datasheet. We are looking at a switching power supply with feedback regulation, not a simple filter.

 

[alexan_e]

I think the circuit will work with bad performance as ripple content will be very high.

Even if it does work as you say , what is the point of a regulator that introduces a very high ripple?
So what do we define as a working circuit?

I'm not sure what you suggest, the datasheet recommends to use inductor values based on the table they provide for optimum performance, do you disagree with the manufacturer recommendation?

 

[manishanand14]

Dear alexan_e!

Even if it does work as you say , what is the point of a regulator that introduces a very high ripple?
So what do we define as a working circuit?

I completely agree.

 

[alexan_e]

Dear alexan_e!


I completely agree.

I'm completely confused now... 8-O

 

[maxseeley]

Please read the following application note:

**broken link removed**