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Full bridge for driving brushless DC motor

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elste_kg

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Hello!


I have a problem with driving DC motor in full bridge. I use PIC16F873 to control the module. It produces PWM of 1000Hz with duty cycle of 10% up to 60%. My motor works on 160V DC and I put it into a full bridge but when I wanted to start it nothing happened. Upper two transistors (IRF4PC40AF) and their driver ICs (HCPL3150) burned up. I made EXACTLY as stated in scheme provided by microchip and now I don't know what to do.
Anyone who can help me ? Thanks in advance.
 

elste_kg

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Here is the PDF schematic. Connectors B1G stands for Base 1 Upper of IRF, B1D - Base 1 lower for IRF etc...
 

plusminus

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Maybe this link will help: http://electronicdesign.com/Files/29/10130/10130_01.pdf it describes how the bootstrap circuit is working. (especially 'How does the high-side driver support a high-voltage MOSFET? ' )

Be sure there is never an overlap between the high side drive and the low side drive (not even for a short time) you can prevent that by adding a death time between switching from the high to low or vice versa.

Where is R17 connected to? it looks like it is for current limiting, but then is must be connected to the bottom of the low side.

Do you also have the schematic of the power part?
 

Siniša

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Your 16V supply is too low. When you substract drop of voltage across diodes D1 and D2, you come too close to minimum operating voltage of your driver IC (15V). Not to mention that at very end of ON period capacitors might have already exhausted charge from Ec2 and Ec3 and just when its needed to shut down upper transistors you dont have any juice left and they remain open because of gate capacitance of main transistors. Increasing frequency might reduce that problem.
You might also want to double check that there is no leakage path that could bypass D1 and D2 because it sounds looks like you do. If dirty PCB or anything else allows current to flow when those diodes are reverse polarised, both your dirver IC and be junction of main upper transistors would be inversely polarised with 160V.
If you are building just one unit and don't have experience with bootstraping circuits, might save you headache to use small transformer with dual 18-20V secondaries to build couple of independant floating supplies for upper gate drivers. Otherwise, try bootstraping with small main voltage first and look with scope what is happening to gain insight how circuit operates. After you got some confidence with your circuit, go with 160V.
 

elste_kg

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Thank You very much! R17 is used as indicator for over current. It is connected to emitters of lower transistors. The bridge and the motor are wired in standard H-bridge.
The switching sequence is:
First set high one of two direction pins.
Start PWM
(Working period)
Stop PWM
Set low direction pin
Wait 1sec
Set high pin for opposite direction
Start PWM
(Working period)
Stop PWM
Set low direction pin
...
 

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