Could you please explain in more detail what you mean by "driving" the capacitive load. Are you trying to limit the current? If so, to what value. Or are you trying to charge the capacitor as quickly as possible?I am trying to drive an high capacitive load with a P-Mosfet.
That would apply near 100V to Vgs which would zap the MOSFET.R35 it too high.... try something like 100 Ohms
What issue? More specifically, what is it that this circuit is supposed to do and what are the constraints? How fast does the capacitor need to be charged (and what constitutes "being charged")?Hi,
I am trying to drive an high capacitive load with a P-Mosfet.
I added a PTC to limit the current, but it doesn't seen to be working. The mosfet is often killed.
Can anybody help and provide a 'simple' solution to this issue please ?
Here is the schematics.
Thanks !!
yes, I'd like to limit the current. 1 to 5A max will be OK.Could you please explain in more detail what you mean by "driving" the capacitive load. Are you trying to limit the current? If so, to what value. Or are you trying to charge the capacitor as quickly as possible?
Yes, I understand that now.The PTC is too slow to provide any protection for this circuit.
It would appear that you are greatly exceeding the safe-area operation for Q3 (Figure 7 in the data sheet).
You could add a resistor in series with the MOSFET to reduce the peak current.
How fast do you need to charge the capacitor?
What is the input signal?
What issue? More specifically, what is it that this circuit is supposed to do and what are the constraints? How fast does the capacitor need to be charged (and what constitutes "being charged")?
How frequently is this being pulsed?
How wide is the pulse?
The transistor (at least the Vishay one I found) has an absolute max drain-source voltage rating of 100 V, so you are asking it to work right at its absolute max rating. Not good engineering.
It has a max drain current of 1 A (at room temperature) and a static on-resistance of less than an ohm, so you are initially asking it to conduct as much as 100 A briefly when the max pulsed drain current is 8 A (and it is likely well below that for the power you are asking it to dissipate during the pulse).
You might put a series resistor inline with the transistor to limit the current to something reasonable, though with 100 Ω load resistance, you can't put too much before you really start decreasing the voltage that the cap can be charged to. If necessary, you could put a second FET across this resistor that shorts it out after the capacitor voltage has risen above a certain amount.
You say that the input voltage can be "up to" 100 V. What can it be "down to"?
What does the Power-Source consist of ?To design a workable Circuit requires ALL the information that You can come up with.
And, of course, You want it to fit on a Circuit-Board the size of a Quarter.
The N-FET should be replaced with a Voltage-Regulator and an Op-Amp, or similar.
1)
What does the Power-Source consist of ?
Why does it's Voltage vary ?, is it a Solar-Panel ?
What is it's absolute-maximum Voltage ?
What is it's minimum-Voltage ?
2)
Is this Circuit going inside of an Aluminum-Box that could be used for a Transistor-Heat-Sink ?
3)
What is the minimum-Voltage required to insure that the Inverter operates correctly ?
What is the maximum-Input-Voltage of the Inverter ?
4)
What Turns-On the Gate of the N-FET ?
Any other information may be important as well.
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sorry, but I don't understand.What prevents current being taken from the capacitor for the load BEFORE the capacitor has finished charging?
You have a load attached to the capacitor (represented by a 100Ω resistor). What prevents this load taking current whilst the capacitor is still in the process of being charged, which you say can take as long as a second?sorry, but I don't understand.
nothing, but it's just a simulation of DC/DC with lights ON.You have a load attached to the capacitor (represented by a 100Ω resistor). What prevents this load taking current whilst the capacitor is still in the process of being charged, which you say can take as long as a second?
it's a simulation of the DC/DC input/filter capacitor.Whats the purpose of the 500uF capacitor?
it could be an idea, but my PCB is way to small to put a relay (especially a 100V relay).What prevents current being taken from the capacitor for the load BEFORE the capacitor has finished charging?
This is often achieved by a resistor and a relay, so that the capacitor charges through a resistor and the relay shorts out the resistor when the capacitor has charged to be close enough to the supply voltage to prevent a huge current spike.
Its unlikely a DC/DC converter would be as large as that... have you measured the inrush current on representative DC/DC converters?it's a simulation of the DC/DC input/filter capacitor.
i've opened some DC/DC 100V input / 12V 10-20A ouput, there are either 100uF or 220uF.Its unlikely a DC/DC converter would be as large as that... have you measured the inrush current on representative DC/DC converters?
by Jake Hertz
by Aaron Carman
by Aaron Carman