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

 

Why do you need to charge a cap up to such a high voltage?

 

Hello,

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

Bertus

 

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.