# Control logic for Mosfet

#### lesdox7

Joined Apr 3, 2024
10
Hello,

I'm working on an energy harvesting circuit known as an in-house harvesting circuit (cc-ih) and would appreciate some guidance on implementing it in Simscape within Simulink.

Circuit Description: The circuit is designed to harvest energy using the following key components and process:

1. AC Source and Rectifier: An AC voltage source feeds into a full-wave bridge rectifier consisting of four diodes. This setup converts the AC input into a DC output.
2. Capacitor Charging: The rectified voltage charges a capacitor, which stores the harvested energy.
3. Voltage Monitoring: A voltage sensor monitors the voltage across the capacitor.
4. Control Logic with MOSFET Switching:
• The control logic monitors the capacitor voltage.
• Once the voltage reaches a threshold of 2.4V, a MOSFET is triggered to connect, allowing the capacitor to discharge through a resistor (acting as a load).
• The MOSFET is turned off when the voltage falls below the threshold, allowing the capacitor to recharge.
The problem i am facing is that i am stack at how to create that contro logic for the mosfet. I tried relational operatios combined with constant and logical operators and the voltage wasnt the one expected. i wasnt seeing the capacitor charging and discharging. So i wanted to ask help, if somebody could guide me what blocks to use for the control logic and how to implement it in simscape. My current implementaion(the control logic is missing) is this one:

#### LowQCab

Joined Nov 6, 2012
4,199
1) How is this Circuit supposed to "harvest" "Energy" ?, "Energy" from what source ?

2) Where, and by what means, will the "Energy" be stored for later use ?

3) What does the word "Energy" mean ?
( Energy must usually be converted into a useful form, a process that always involves definite losses )
( In this case, I suspect that the word "Energy" is being heavily misused and is nothing but a "Buzz-Word" )

4) What does the word "Power" mean ?
( Power is Energy that is already in a useful form, and may be measured as Horsepower or Kilowatts )
( There are, of course, quite a few other terms that may be used in the measurement of Power,
most are convertible to each other via various simple Math-Formulas ).

This Circuit looks like an excellent way to instantly destroy a FET.
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#### lesdox7

Joined Apr 3, 2024
10
1) How is this Circuit supposed to "harvest" "Energy" ?, "Energy" from what source ?

2) Where, and by what means, will the "Energy" be stored for later use ?

3) What does the word "Energy" mean ?
( Energy must usually be converted into a useful form, a process that always involves definite losses )
( In this case, I suspect that the word "Energy" is being heavily misused and is nothing but a "Buzz-Word" )

4) What does the word "Power" mean ?
( Power is Energy that is already in a useful form, and may be measured as Horsepower or Kilowatts )
( There are, of course, quite a few other terms that may be used in the measurement of Power,
most are convertible to each other via various simple Math-Formulas ).

This Circuit looks like an excellent way to instantly destroy a FET.
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.
.
this is a short desciption of the circuit becuase i didnt want to give you a full paper to read. the circuit is described in page 7 of the pdf . its the in house circuit cc-ih. if you dont wont to really read that page, i can try to answer. (also i am not sure what i implemented is right, if i was sure i wouldnt be asking here).1) The circuit is designed to harvest energy from an AC source, such as vibrations converted to electricity via piezoelectric materials, or from ambient electromagnetic fields. The rectifier converts this AC input into DC power, which is then used for charging the capacitor. 2) The energy harvested from the AC source is stored in the capacitor. The questions 3, 4 i dont really think have much to do with what i am askign

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#### LowQCab

Joined Nov 6, 2012
4,199
What product do You expect to achieve with less than 1-miliwatt of Power ?
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#### lesdox7

Joined Apr 3, 2024
10
my friend this is all theoritical. my teaccher just told me to implement this circuit from the pdf using simscape electrical in simulink. so i just have to select the correct blocks and implement the control logic so that the mosfet turn on and off based on the threshold votlages so that the capacitor charges and discharges in the correct way. i really must not give so attetiont to the theoretical part as i am just asked to implement a model in simscape. thanks in advance!

#### LowQCab

Joined Nov 6, 2012
4,199
You will need Four "Active-Ideal-Diodes", ( Full-Wave-Active-Rectifier-Circuits ),
these can also be hand-assembled from Four Op-Amps and Eight Generic-Diodes.
The Outputs of the Active-Rectifiers must have a ~1K-Resistor before the Capacitor.

Use a ~1uF Film-Capacitor to store the accumulated Voltage.

A Photo-Voltaic-Gate-Driver can be used for isolating the FET from the Micro-Controller-Output,
or, instead of a Micro-Controller, You can use a simple 7555-Timer to short the Capacitor on a schedule.

There is no point in measuring the Discharge-Current of the Capacitor,
just measure the Voltage-Increase over a pre-set Time-Period, reset, repeat.

If the Time-Periods seem too short, simply increase the size of the Capacitor.
You may also increase the Resistance of the Output-Resistors.

Your present Circuit provides no Over-Voltage-Protection for any of the Components,
so be sure to at least include a TVS on the Input.
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