It's a good idea to isolate the PIC from the power electronics as much as possible. You can use any any opto you want provided itmeets the switching requirements you have. In my Electronic Speed Control (6-30V, 100A), I approached it from the other direction - I isolated the PIC from the "master" side (PIC was a slave to it, driving FETs). The PIC derived it's power from the batteries which ran the motor, but through an LC circuit which blocked the switching noise. The PIC and FETs shared a common ground, used a MIC4427 to drive the FETs. V+ went into an inductor etched onto the PCB, into a big cap C1 (220uF). Other side of C1 went into a 5V LDO regulator, which had 1.0uF and 0.1uF on its outputs. These fed the PIC, which had one pin driving the 4427 (both inputs) with a pull-down for fail-safe. C1 also fed a 12V regulator which provide gate drive voltage to the FETs (through the 4427), which had a 22ohm resistor on the gate to control slew. I had to design around several things: 75 MHz AM radio receiver which didn't need any more interference, 60 Hz refresh rate of digital data from radio, Variable "frequency" pulse-position-modulated data (standard RC data), 4 MHz oscillator on the PIC, 3 kHz PWM frequency to the motor. Works well! Andy Nicholas Irias on 06/27/2000 11:25:06 AM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: (bcc: Andrew Kunz/TDI_NOTES) Subject: [EE]: Optical isolation for FET driver? I am using a pair of Micrel 5022 half-h-bridge drivers to drive large FETs for motor control (20 amp x 24 volt application), and am wondering what the appropriate level of isolation is to prevent glitching on the PIC that will be providing the input signals to the Micrel 5022s. Micrel says that the ground for the 5022 driver should be connected to signal ground rather than the power ground, and that Vcc should be connected to the motor power supply, which is to be decoupled with a 10uF capacitor. I assume that the decoupling capacitor is connected to the motor power supply ground rather than to the signal ground. My concern with Micrel's recommendation is that I will create some sort of ground loop or otherwise get noise into the PIC through the signal leads. Would it be adviseable to use optical isolation on the input signals, with a separate 5v regulator to create power the optical isolator?