boostinductor
I have a circuit that boost voltage from 12V to 120V, the problem is the current in inductor is too big, around 5A, the circuit and the simulation in LTSpice is like this
the red line is the current, and the blue line is the voltage across zener diode, i just want to the big voltage without much current. how can i limit the current for around 1A? it is okey for the voltage to have a longer settling time
thank you
I noticed that all your mosfets are N-channel.
It would be easier to use P-channel mosfets for M2 and M3, since the Vgs is more stable than for NMOS.
I think the behavior you're seeing in the waveforms is because Vgs is varying with the current through R1.
From http://www.learn-c.com/experiment7.htm:
There is a bit of a problem when a MOSFET is used for Switch A or Switch B. The Drain is connected to the V+ for the motor and the Source to the motor. If the gate is then made to be 2 volts greater than the Source, the MOSFET will turn on. When that happens however, the voltage at the Source will increase until the gate is no longer 2 volts greater than the Source and the MOSFET will turn off. Another voltage source is needed that is always greater than Motor V+ by at least 2 volts.
TLRD: your calculations are fine. I got myself confused by checking them against a different calculator that targeted DCM not CCM. I'm not gonna change the stuff below because Arsenal replied to it, and it might also be useful to you to compare the two modes.
Your inductor looks an order of magnitude too big vs what I get at https://learn.adafruit.com/diy-boost-calc/the-calculator
And it does look like your inductor is far too big:
@Arsenal N.B.: I figured out the difference between these two calculators. The adafruit one gives you a DCM (discountinous current mode) solution, whereas TI's gives a CCM solution.
Which one is preferable depends on various factors. Basically at high output currents you want CCM to lower the losses and stresses on the components, but DCM has better transient response. A lot more about that can be read here, including a side-by-side power efficiency calculation example.
Best Answer
The problem is for higher current at startup is due to charging of output cap C1 which is usually called as inrush current. This inrush current will last longer till the output cap charges to input voltage level. Once output reaches input voltage level diode blocks it.
This type of problem will exist in "Hot plugging" system like battery.
Inrush can be approximately calculate by
Ipeak = Vin * sqrt(Cout/L)
approximate pulse time can be calculated by
Tpulse = Pi * sqrt(L * Cout)
There are two ways to solve this problem practically
1) Passive inrush current limiter
2) Active inrush current limiter
Passive inrush current limiter
This system includes Resistor (approx around 10 to 20 Ohm depends on practical application)
Resistor uses is of Thermistor (Resistance will drop due to rise of temperature which is due to current) type. This has its own disadvantage, resistor will get heat up lot since whole load current will pass through R1 & R2
Active Current Limiter
This includes Switch S1 in addition to R1&R2. S1 may be mechanical relay or any power electronics switch like Mosfet, SSR along with its control circuit.
This will serve the purpose but will include additional cost and complexity.
If there is any control over input voltage from previous stage can be solved. For simulation purpose try programmable input voltage source.