MOSFET Driver for Boost Converter Design: A Look into IRF8707PBF and MAX4420

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In summary, MOSFET driver plays an essential role in the design of boost converters, providing the necessary gate drive signals to control the switching of MOSFETs. Two popular options are the IRF8707PBF and MAX4420, both offering high efficiency and reliability. The IRF8707PBF is a low-side driver with low input and output capacitance, making it suitable for high-frequency applications. On the other hand, the MAX4420 is a high-side driver with a wide input voltage range and built-in protection features. Both drivers have their advantages and can be chosen based on the specific needs of the boost converter design.
  • #1
gnurf
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Dear Oracle,

I'm designing a boost converter where the input is a current limited (~500mA) voltage source that varies from 3.5V to 6V. The output (load) varies from 7V to 9V. I intend to drive a MOSFET, IRF8707PBF [1] from IR, with a 250kHz PWM control signal via Maxim's driver IC MAX4420 [2].

Do you see any unforeseen mis-happenings in your crystal ball, if I chose to mate the two devices at the given frequency and voltages?

Other comments/questions on driving MOSFET's or on the boost topology in general are welcomed.


[1] https://ec.irf.com/v6/en/US/adirect/ir?cmd=catSearchFrame&domSendTo=byID&domProductQueryName=irf7807apbf
[2] http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1486
 
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  • #2
gnurf said:
Dear Oracle,

I'm designing a boost converter where the input is a current limited (~500mA) voltage source that varies from 3.5V to 6V. The output (load) varies from 7V to 9V. I intend to drive a MOSFET, IRF8707PBF [1] from IR, with a 250kHz PWM control signal via Maxim's driver IC MAX4420 [2].

Do you see any unforeseen mis-happenings in your crystal ball, if I chose to mate the two devices at the given frequency and voltages?

Other comments/questions on driving MOSFET's or on the boost topology in general are welcomed.


[1] https://ec.irf.com/v6/en/US/adirect/ir?cmd=catSearchFrame&domSendTo=byID&domProductQueryName=irf7807apbf
[2] http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1486

Why is your output voltage going to vary? Or do you mean that you are going to make the output adjustable?
 
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  • #3
berkeman said:
Why is your output voltage going to vary? Or do you mean that you are going to make the output adjustable?

It's the power stage of a maximum power point tracking solar cell to lithium-ion battery charger -- i.e., the output is the battery voltage with a (float voltage) Vmax =~8.2V, (and not 9V as I said in the OP). I'll sense the output current from the converter and battery voltage into a uC ADC and implement a software MPPT algorithm that will generate the PWM output to the mosfet driver. I'm thinking a state machine with a MPPT constant (max) current state, and a constant voltage state where I'll move away from the MPP as necessary, as a start. Having said that, placing a uC in the feedback loop muddies the already murky waters for me, so I'm struck with bursts of confusion from time to time..

I was just looking to bounce some ideas of someone with a little more than my non-existing experience. Thanks.
 
  • #4
What made you choose 250kHz for the switching frequency. Have you considered the trade-off's of going higher/lower?
 
  • #5
If your source voltage is 3.5V, that won't be enough to turn your mosfet completely on. Looking at the datasheet, you need at least 4.5V on the gate to completely turn the mosfet on. It will work, but you will be loosing a lot of power at low input voltages, especially if your battery is low and drawing a lot of current.
 
  • #6
uart said:
What made you choose 250kHz for the switching frequency. Have you considered the trade-off's of going higher/lower?

I need the system to be fairly small while still being efficient. Basically I've tried to squeeze the frequency down as much as possible to minimize switching losses, while at the same time not letting the inductor and capacitor occupy too much pcb real estate. By using the expression for Lmin (see page 11, http://focus.ti.com/lit/an/slva061/slva061.pdf" ) with fsw = 250kHz, I've decided to go with a 82uH (torodial for less EMI?) inductor in an attempt to gain some foothold somewhere from where I can proceed.

famousken said:
If your source voltage is 3.5V, that won't be enough to turn your mosfet completely on. Looking at the datasheet, you need at least 4.5V on the gate to completely turn the mosfet on. It will work, but you will be loosing a lot of power at low input voltages, especially if your battery is low and drawing a lot of current.

Yes, maybe http://www.national.com/pf/LM/LM5112.html#Overview" from National is a better choice. Similar switching speeds and current consumption at 250kHz from what I can see.


Thanks for the questions/comments. It helps, so don't be shy now! :)
 
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  • #7
I just realized the Output Resistance is higher on the LM chip than the one from Maxim (30 ohm vs 1.5 ohm), but I was prepared to place (as a saftey measure) a small resistor on the gate input anyway to dampen any ringing oscillations that might occur.

As long as fsw is relatively low at 250kHz, the bigger Rout of LM5112 should not pose a big problem, right?
 

Related to MOSFET Driver for Boost Converter Design: A Look into IRF8707PBF and MAX4420

1. What is a MOSFET and what is its function in a circuit?

A MOSFET (metal-oxide-semiconductor field-effect transistor) is a type of semiconductor device that is commonly used as a switch or amplifier in electronic circuits. It works by controlling the flow of current between its source and drain terminals through the use of an electric field.

2. What is a driver and how does it work with a MOSFET?

A driver is an electronic circuit that is used to control the operation of a MOSFET. It provides the necessary voltage and current to the MOSFET's gate terminal, allowing it to switch on and off according to the input signal.

3. Can I use any MOSFET with any driver?

No, it is important to select a MOSFET and driver that are compatible with each other. This includes considering factors such as voltage, current, and switching speed requirements.

4. What are the advantages of using a MOSFET and driver combination in a circuit?

MOSFETs and drivers are commonly used in power electronics applications because they offer low power consumption, high efficiency, and fast switching speeds. They also have a high input impedance, making them easy to drive with low-power signals.

5. How do I ensure the reliability of my MOSFET and driver circuit?

To ensure the reliability of your circuit, it is important to use high-quality components from reputable manufacturers and follow proper design guidelines. It is also recommended to perform thorough testing and monitoring during the development and operation of the circuit.

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