[last updated: 2025-08-14]
MPPT charge controllers
-----
- Mosfets have three terminals: Source, Drain, and Gate.
The Source is connected towards the negative voltage
and the Drain is connected towards the positive voltage
- Mosfets can be used as switches, full-on to full-off, or as virtual voltage-controlled resistors.
In a switch mode, they can be fed with a PWM gate signal, resulting in an effectively variable/controllable output.
- Two main categories of mosfets:
Note: there are other classifications as well, but these are the main two.
Every mosfet will have some value in each of these two categories.
------------------------------------------------------------------------------------
- Operation:
- To keep this explanation simple, I'll just consider n-channel enhancement mosfets.
- Recall enhancement mosfets are off until they're turned on by a proper gate signal.
- A "proper gate signal" means proper polarity and value/magnitude.
- Magnitude is always in relation to Source voltage (which will be different in different circuit configurations).
In fact, the gate voltage level is often symbolized as: Vgs = Vg - Vs
Further, Vgs must be greater than the Threshold voltage of your part. This parameter, VTH
is listed in your mosfet's data sheet and will be different for two different mosfet models.
- Polarity is determined by whether you have a "p-channel" or an "n-channel"
If n-channel, VGS must be greater than Vs, by at least the Vth amount.
If p-channel, VGS must be less than Vs, by at least the Vth amount.
-
------------------------------------------------------------------------------------
- Links/Refs:
------------------------------------------------------------------------------------
- Addendum...
- p-ch have higher on-resistance than n-ch
- Using an N-channel MOSFET as a high-side switch is possible, but it requires the gate voltage to be significantly higher than the source voltage to turn it on, which can complicate the circuit design. Generally, P-channel MOSFETs are preferred for high-side switching due to their simpler operation.
- IRF mosfets need ca 10V at the gate to fully turn on.
IRL mosfets need ca 5V at the gate to fully turn on.
- A MOSFET is like a variable resistor. The Gate-Source voltage controls the Drain-Source Resistance.
When there is no voltage between the Gate-Source , the Drain-Source resistance is very high, effectively an open circuit.
- N-channel: The Source is connected to ground. To turn it on, apply a voltage to the Gate. To turn it off, ground the Gate.
- P-Channel: The Source is connected to Vcc. To turn it on, connect the Gate to ground. To turn it off, connect the Gate to Vcc.
------------------------------------------------------------------------
- Circuits:
.
.
.
eof