RussianKid
New Member
Hi!
I am currently researching H-Bridges to drive bipolar stepper motor using a PIC (PIC18F2550 to be precise). Since this is in the context of a CNC machine/milling machine conversion, the drive system has to be quite (very) powerful (60V maximum, at variable currents - 12A maximum).
I have done and prototyped most of the parts of this, however, there is one thing I do not quite understand. As far as I understand, a normal H-Bridge is as in the 'Normal H Bridge.jpg' attachment, however, especially in applications involving MOSFETs, I have increasingly encountered H Bridges where the transistors (or MOSFETs) are all the same polarity (the 'Abnormal H Bridge.pdf' attachment exemplifies one such application). That is by no means an isolated example, as the same is found in RC car electronic speed controls.
More specifically, I do not understand how the transistor/MOSFET to the emitter/source of which the load is connected can switch on/off: surely if the vast majority of the voltage drop occurs on the load, then the potential difference between the emitter/source and the base/drain disappears, thus stopping the transistor/MOSFET from opening? (the simplified version is demonstrated in Simplified.jpg).
I am specifically interested in how H Bridges which all use the same polarity work, as my chosen MOSFET source OnSemi has N Channel MOSFETs with a minimal internal resistance of 9.5 mΩ, but P Channel of 80 mΩ, hence, using an N Channel MOSFET is not only cheaper, but also reduces heating during operation. The data sheet of the specific MOSFET I have in mind is also attached.
Thanks in advance, and sorry for the long post!
Alex
I am currently researching H-Bridges to drive bipolar stepper motor using a PIC (PIC18F2550 to be precise). Since this is in the context of a CNC machine/milling machine conversion, the drive system has to be quite (very) powerful (60V maximum, at variable currents - 12A maximum).
I have done and prototyped most of the parts of this, however, there is one thing I do not quite understand. As far as I understand, a normal H-Bridge is as in the 'Normal H Bridge.jpg' attachment, however, especially in applications involving MOSFETs, I have increasingly encountered H Bridges where the transistors (or MOSFETs) are all the same polarity (the 'Abnormal H Bridge.pdf' attachment exemplifies one such application). That is by no means an isolated example, as the same is found in RC car electronic speed controls.
More specifically, I do not understand how the transistor/MOSFET to the emitter/source of which the load is connected can switch on/off: surely if the vast majority of the voltage drop occurs on the load, then the potential difference between the emitter/source and the base/drain disappears, thus stopping the transistor/MOSFET from opening? (the simplified version is demonstrated in Simplified.jpg).
I am specifically interested in how H Bridges which all use the same polarity work, as my chosen MOSFET source OnSemi has N Channel MOSFETs with a minimal internal resistance of 9.5 mΩ, but P Channel of 80 mΩ, hence, using an N Channel MOSFET is not only cheaper, but also reduces heating during operation. The data sheet of the specific MOSFET I have in mind is also attached.
Thanks in advance, and sorry for the long post!
Alex