switching frequency of LM can be adjusted to any value between kHz and .. mode. All the analysis in this datasheet assumes operation in continuous . Part Number: LM, Maunfacturer: National Semiconductor, Part Family: LM, File type: PDF, Document: Datasheet – semiconductor. Datasheets, LM Design Resources, LM Design with WEBENCH® Power Designer. Featured Product, Create your power design now with TI’s.
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Duty cycle Next, compute the duty cycle, D. There is a second resistor which goes between the current sense pin of the converter and the current sense resistor.
I think I will have to look at other chips such as the LT Again, Adafruit gives this as 4. The second zero, z2, is caused dwtasheet the inductor and the load on the power supply.
A boost converter design
These margins are important because the poles and zeros shift with varying load and input voltage, and without these margins your circuit could go unstable. Now that we have our pole and zero frequencies, we need to know what the DC gain is.
If Q were infinite, the thing would vibrate itself to pieces and catch fire at om3478 the switching frequency. This means raising the frequency or the inductance by at least a factor of 3. And, of course, this pole is located at half the switching frequency: That is all before you get to the need to plot charts to solve the equations. So based on the inductance and current, I can choose an inductor that can handle this current. Again, this is from the Adafruit calculator, but here is the formula: And so I get a sense resistor of 0.
The pole is caused by the output capacitor with lk3478 load, and the complex pole is caused by the switching action. One of these is the resistor that goes between the switch and ground. If you don’t know anything about control theory, you probably want to skip this section.
A boost converter design | Details |
After the design procedure, here’s what I ended up with: Here’s the one for the boost converter:. The LM datasheet provides a nice series of design procedures for various converter topologies.
About Us Contact Hackaday. Let’s locate the zeros: The first zero, z1, is caused by the output datashete with its ESR. Note that the Adafruit calculator correctly, in my opinion uses the lowest datahseet two possible duty cycle based on the minimum input and output voltage, because this will result in the highest minimum inductance. It can handle currents up to 9A, and has an on-resistance of 0. The problem is, without knowing control theory, it will be difficult to select the compensation components.
I chose kHz because I wanted it to be above the minimum, but not so fast that all my components had to be super-fast. We’ll find out in the next project log. So with a maximum input voltage of 12V, and an output current of 0. The top plot is gain in dB vs frequency in Hz, and the bottom is phase shift in degrees vs frequency in Hz. Here we see the gain margin is 3. The datasheet doesn’t state this, but ideally the gain margin should be somewhere between 6 and 12 dB. However, we now do not need a slope compensation resistor, and everyone is happy.
I don’t know, but suspect that the output voltage of the adapter will drop under load, so I’m just going to go ahead and specify a minimum input voltage of 8VDC. It can withstand at least V to the drain, and has a l3478 threshold of at most 4V. You want something big with low ESR. We can see that unity gain occurs at 2. We need to find Q, which is the damping factor. Again, Adafruit correctly is using the D based on the maximum input voltage, but I’m using a higher value for extra safety margin.