# Tag Info

## Hot answers tagged mosfet

4

If you are using the IRLB8721 simply because it's what is in your component drawer then you can simply parallel multiple devices. While current sharing will not be exact between devices, the power dissipation will reduce with the square of the current flow through each device. For example if the RDS(on) achieved is close to 16 mOhms with your current 5V ...

4

Let's see how bad this looks... According to the datasheet Vds max = 30V, what is much higher than 11.1V, so you are good in this regard. Let's check the power dissipation @ Id=20A. According to Fig. 12 of the datasheet, the Rdson degrades significantly when Vgs=5V instead of 10V. For Tj=125˚C (worst case), Rdson=16mΩ. So the power dissipated will be 0.016*...

3

If the module you bought contains a real LTC3780, you do not need any downstream protection for it, as it is already short circuit protected. If the chip on there is made of chinesium, and you do not trust it, you can try and hack the board to regulate the inrush current changing the cap connected to the SS pin. Limiting the inrush current will surely also ...

2

The top one is possibly a TPS3809K33DBVT supply voltage supervisor (2.93V), suitable for a typical 3.3V microcontroller. The bottom one is almost certainly a 16MHz crystal, given the small NP0 capacitors on either side.

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Will it work at 11.2V? Yes because when its's working the Vds is still only <0.1V and Vds max is 30V =BVdss when it is off. How do you know if the FET will work? Here, It can if you have a really good heatsink or you can invert the driver with an NPN and use the >=10V gate rated voltage RdsOn rises 50% at Vgs=5V from the rated value at Vgs= 10V for ...

2

NOTICE the behavior at Vt only guarantees 250uA thru the drain. You need Gvate to be much greater than 2.4 volts. Are there curves? The 3rd line (spec) up from bottom, in the 2nd table, shows 30amps AT 25 degree Centigrade CASE TEMPERATURE with 10 volts on the gate. The 2nd line (spec) up makes promises about 4.5 volts. Thus 3.3 volts on gate is risky ...

2

Indeed $V_{GS}$ should not exceed the maximum rating of 20 V. That 2.4 V is the maximum threshold voltage, so some devices may have a threshold voltage of 2.4 V. If you'd then apply a $V_{GS}$ = 2.5 V the "overdrive" would be only 2.5 V - 2.4 V = 0.1 V which isn't a lot. The MOSFET will probably not turn on fully. What I usually do is apply a $V_{GS}$...

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The irlb8721 data sheet says the max continuous drain current at T=25 Celsius is 62A for Vgs=10V. Of course, your load component(s) needs to be able to take that current as well.

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KVL is invariant in the absence of changing magnetic fields (see @Jonk's comment). KCL is just invariant (as long as you account for charge injection phenomenon like corona discharge). So, yes, you can use KVL around a transistor. If it helps, just relabel the terminals as "point A", "point B", etc. If you know the voltage from point A to point B, and ...

1

I won't say a blanket "yes," since I'm not totally sure what you are asking. Looking at your examples, though: Yes, if you know $V_{sd}$ and $V_{dg}$, you can easily calculate $V_{sg}$ as you describe. To check the signs, expand each of the terms $V_{xy}$ into $(V_x - V_y)$. This gives: V_{sg} = V_s - V_g = (V_s - V_d) + (V_d - V_g) = V_{sd} + ...

1

The FET is turned on when VBUS is not present. If you had only a diode, current could flow only from the battery through the diode and into your circuit. Using this approach, current can flow in both directions. You can attach a battery charging circuit of the correct voltage to the "JST LIPO INPUT" and run the board and charge the battery without ...

1

The FET comes with a "free" body diode (due to its construction) so it has to be connected this way. If it was the other way around, then current would flow through the body diode from VBUS (presumably +5V) into VBAT (it's a LiPo, so 4.2V max), which would overcharge the battery in an uncontrolled and probably spectacular way (ie, boom). In fact, the FET ...

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