High Voltage, Highside MOSFET switch using Bootstrap Driver

Discussion in 'The Projects Forum' started by mil112, Sep 28, 2010.

  1. mil112

    Thread Starter New Member

    Sep 28, 2010
    2
    0
    Purpose:

    I want to use the high side, high voltage switch to charge a capacitor to 200V then open the switch and leave the capacitor charged.

    Attachments:

    A schematic and 4 plots

    Current progress:

    I am using the FAN7390 Gate Driver for this application. The schematic of my system is attached with the latest component values (they change based on operating frequency.)

    The best response I have had is shown in plot 1. Most of the time the output is a perfect square wave, but occasionally the rise time becomes limited. I am not sure why. The component values in this case were:

    RB = 5 ohm
    CB = 470 nF
    R1 = 5 ohm
    R2 = 1 Mohm
    R5 = 50 ohm
    load = 1 Mohm

    I have been unable to repeat the results in plot 1. Typically the results are as shown in plot 2 (at 4kHz). Where the rise time is limited for some reason. the components in this case were:

    RB = 5 ohm
    CB = 100 nF
    R1 = 5 ohm
    R2 = 1 Mohm
    R5 = 50 ohm
    Load = 1 Mohm

    Plot 3 indicates my actual application where I need to charge a capacitor and leave it charged. In this case the slow rise time is limiting my frequency. the components in this case are:

    RB = 5 ohm
    CB = 20 nF
    R1 = 1 ohm
    R2 = 10 kohm
    R5 = 50 ohm
    Load = 4 nF

    CB was reduced because at higher CB the voltage would drop about 50V when the control signal goes to zero.
    certain R2 and R5 values can cause vout to drop close to zero then recharge slowly when vin goes to 5V.

    A situation where the components are not ideal is shown in plot 4. These fluctuations are unacceptable. the components were:

    RB = 5 ohm
    CB = 60 nF
    R1 = 1 ohm
    R2 = 10 kohm
    R5 = 50 ohm
    Load = 4 nF

    Question:

    I have changed many of the components but the rise time does not seem to be effected. Does anyone know what components in this circuit will alter the rise time? I would like to switch at >10kHz and fully charge the capacitor (to 200V) at each switching event. Any other ideas that could fix my problem?

    Thanks in advance for any help!

    Mike
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Why do you need to charge a cap up to such a high voltage?
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    Why do you need such a high voltage?
    What is used as actuator? (do you have specs for that)

    Bertus
     
  4. mil112

    Thread Starter New Member

    Sep 28, 2010
    2
    0
    Thanks for the responses.

    The actuator is a piezoelectric actuator. Electrically it can be approximated as a capacitor. The high voltage is necessary to cause deflection of the actuator. My circuit is intended to address an array of actuators using a single supply.
     
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