Using a MOSFET and comparator together as a switch

In summary, the speaker is seeking advice on using a MOSFET and comparator in a solar charger to prevent overcharging of batteries. They need a comparator with an internal reference voltage of 5.5V and a MOSFET rated for 100 mA. A solution is suggested using a standard voltage comparator and a separate voltage regulator, with resistors to achieve the desired voltage. The speaker is also reminded to include hysteresis in the comparator's positive feedback to avoid noise issues. Alternatively, they could use a voltage regulator set at the desired cutoff voltage to stop charging when the battery reaches a certain voltage.
  • #1
Shinnog
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Hello all, I was advised to use a MOSFET and a comparator together in a solar charger that I am building to stop the solar panel from charging the batteries when full. Seems logical, right? The only problem is I've never used MOSFETs or comparators, so I'm not really sure how to. I need a comparator with an internal reference voltage of 5.5V and a MOSFET rated for 100 ma. I looked around and found a MOSFET but I couldn't find a comparator with an internal reference voltage... does anyone know where I could find one? And once I do find one how to hook it all up?
 
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  • #2
You should use a standard voltage comparator along with a separate 3-terminal voltage regulator like the Motorola MC7806 (see
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-21/DSA-405486.pdf
and use two resistors (voltage divider) to get 5.5 volts.
 
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  • #3
Be sure to put a couple hundred millivolts of hysteresis into your positive feedback on the comparator, to avoid noise switching and buzzing.
 
  • #4
You want to stop charging when the battery reaches a certain voltage? Just charge the battery with the output of a voltage regulator set at that cutoff voltage. It'll cut off the current when the battery voltage reaches the output voltage.
 

What is a MOSFET and comparator switch?

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and comparator switch is a circuit that uses a MOSFET and a comparator to control the flow of current through a load. The MOSFET acts as a switch, while the comparator compares two input voltages and outputs a high or low signal to control the MOSFET.

What are the advantages of using a MOSFET and comparator switch?

Using a MOSFET and comparator switch offers several advantages over traditional mechanical switches, such as faster switching speed, lower power consumption, and higher reliability. It also allows for more precise control of the current flow.

How do you connect a MOSFET and comparator together as a switch?

To connect a MOSFET and comparator together as a switch, the output of the comparator is connected to the gate of the MOSFET. The source of the MOSFET is connected to the ground, and the drain is connected to the load. The comparator's two input voltages are connected to the desired control signals, such as a temperature sensor or a microcontroller.

What are some common applications of a MOSFET and comparator switch?

A MOSFET and comparator switch can be used in a variety of applications, such as in power supplies, motor control, battery charging, and lighting control. It is also commonly used in electronic devices that require precise and efficient control of current flow.

What are some potential issues to consider when using a MOSFET and comparator switch?

One potential issue to consider is the voltage tolerance of the MOSFET. If the input voltage to the comparator is too high, it can damage the MOSFET. Additionally, the comparator's output may need to be buffered to ensure the MOSFET is fully turned on or off. It is also important to consider the load's voltage and current requirements to select an appropriate MOSFET and comparator for the application.

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