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  1. #1
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    Translating a FET drive signal up in voltage

    Hi
    We need to switch some PWM dimming FETs on and off. These FETs sit on top of a 100V rail and the driving micro sits at 0V…therefore we need to translate the drive signal up in voltage.
    We can either use a SI8710 digital isolator, or a IRS25752 bootstrap driver. The IRS25752 looks a hands down winner as its cheaper, smaller, and uses less bias current.

    Can you think of any disadvantages of the IRS25752?

    IRS25752
    https://www.infineon.com/dgdl/irs257...53567b388b2839

    SI8710
    https://media.digikey.com/pdf/Data%2...DFs/Si87xx.pdf

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    Re: Translating a FET drive signal up in voltage

    The bootstrap device won't work for static voltages, if that's a concern...


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    Re: Translating a FET drive signal up in voltage

    Thanks, yes, we will feed it a high side bias supply.



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    Re: Translating a FET drive signal up in voltage

    Both drivers need a power supply on top of the 100V rail in this circuit, thus IRS25752 is the cheaper solution.


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    Re: Translating a FET drive signal up in voltage

    Hi,

    Optocoupler, photoMOS, relais...
    Or some kind of switched capacitor circuit...this may avoid extra power supply.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: Translating a FET drive signal up in voltage

    We should know pwm frequency and load current to decide about appropriate driver circuit.



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    Re: Translating a FET drive signal up in voltage

    pwm frequency is 500Hz. Load is just 2 little sot23 fets being driven on/off



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    Re: Translating a FET drive signal up in voltage

    Simple charge pump creates 107V on top of 100V supply rail. Switched by NPN transistor biased by 5V clock signal at 500 Hz. This results in the load getting 7V DC pulses.

    Click image for larger version. 

Name:	charge pump clk NPN cap applies 107V to load ref'd to 100V supply rail.png 
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ID:	154075

    Duty cycle and component values can be adjusted to produce a wide range of volt levels. The simulation has the resistors carrying a few mA.


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