Hello everyone,
I am trying to make a 1/2 to 3/4 HP DC drive for my CNC machine. I decided not to buy because I would rather know how to fix it and want to be able to contribute the project to others.
I made a schematic and attached it. It is merely a concept schematic of how I am thinking of doing the drive. I would really appreciate anyone's critiques about the concept itself. I will explain the circuit's 'operation' from left to right.
So, the input comes in from a 120VAC source (isolated) through a 6-8A fuse. The main bulk capacitor(s) will have a very low resistance FET on the return path to negative. This FET will be picked so that it possesses a lot of gate charge, and more will be added to the base. I need to calculate this circuit, but the idea is to use the linear curve of the FET to absorb inrush.
A 15V supply will be derived from the mains through an integrated solution, namely an ST micro Viper IC. I am using an app schematic, so no worries there.
The middle stage is for line detection. A microcontroller will strobe the line every second very briefly by turning on a fet that drives an optoisolator LED (to reduce resistor power dissipation). It looks for the signal on the other end, if the line voltage is there, then it will detect it and start charging the bulk capacitors. Darn, just noticed I am missing some bleed resistors..
The final stage is a simple PWM circuit. The OPTO Gate drive is an integrated 2A optoisolated gate driver IC, I just didnt have the symbol. The mosfet in parallel with the motor acts as a low-resistance diode.
Am I missing anything? I haven't ever done anything this high voltage and potentially lethal. Oh, nobody build this circuit! It is just a concept and is not safe.
Steve
I am trying to make a 1/2 to 3/4 HP DC drive for my CNC machine. I decided not to buy because I would rather know how to fix it and want to be able to contribute the project to others.
I made a schematic and attached it. It is merely a concept schematic of how I am thinking of doing the drive. I would really appreciate anyone's critiques about the concept itself. I will explain the circuit's 'operation' from left to right.
So, the input comes in from a 120VAC source (isolated) through a 6-8A fuse. The main bulk capacitor(s) will have a very low resistance FET on the return path to negative. This FET will be picked so that it possesses a lot of gate charge, and more will be added to the base. I need to calculate this circuit, but the idea is to use the linear curve of the FET to absorb inrush.
A 15V supply will be derived from the mains through an integrated solution, namely an ST micro Viper IC. I am using an app schematic, so no worries there.
The middle stage is for line detection. A microcontroller will strobe the line every second very briefly by turning on a fet that drives an optoisolator LED (to reduce resistor power dissipation). It looks for the signal on the other end, if the line voltage is there, then it will detect it and start charging the bulk capacitors. Darn, just noticed I am missing some bleed resistors..
The final stage is a simple PWM circuit. The OPTO Gate drive is an integrated 2A optoisolated gate driver IC, I just didnt have the symbol. The mosfet in parallel with the motor acts as a low-resistance diode.
Am I missing anything? I haven't ever done anything this high voltage and potentially lethal. Oh, nobody build this circuit! It is just a concept and is not safe.
Steve