This project was developed in the course of the contactless electrostatic grippers. In order to be able to control the individual gripper zones, it must be possible to supply them with a variable voltage between 0V and 1000V. The necessary current is almost zero, since only the individual gripper electodes have to be charged. In the later gripper design, the circuit sits between the microcontroller and the gripper.
- Variable voltage between 0 and 1000V
- external supply with 1000V DC
- linear voltage regulation
- Input: PWM signal with 3.3V and variable duty cycle
- cut-off frequency 1kHz
- as cheap and simple as possible
Basis is a half bridge circuit with driver "FAN73912mx". This can withstand up to 1200V, but is not isolated, so all GND potentials must be connected. The rest of the circuit is based on the driver's refernce design with a bootstrap circuit to switch the mosfets. Finally, the output is filtered through an RC gate to remove the PWM signal and provide a DC voltage. The switching frequency is 20kHz. The design is certainly not optimal but it does what it should and is perfectly adequate for the application.
The finished circuit board is made so that several can be stacked on top of each other and the supply lines can be looped through.
 |
 |
| single half bridge | stacked half bridges |
The quiescent current is about 3 mA at 1000V and 20 kHz. The minimum voltage resolution depends on the PWM resolution and is e.g. with a 12 bit signal about 0.244 V.
The voltage can be controlled linearly as desired:
