Hi,
I am in the process of building a biploar stepper motor driver, which uses IRF540 MOSFETS for the high and low side switching. The current limiting mechanism is based on figure 4.11 from the "!Jones on stepping motors" we page at this address : http://www.cs.uiowa.edu/~jones/step/current.html.
I say based on it, because I have a slightly different arrangement for the voltage sensing - I use an IRC540 current sensing MOSFET instead of a resistor. I also have a Microchip PIC driving 2 * DACs to provide the reference voltages for the comparators and the logic is all 4000 series with a VCC of 12v.
I originally had 4000 series chips with a Vcc of 12v driving the gates of the MOSFETs. This gave me problems because when I did the design I hadn't realised the problem of driving high side MOSFETS in a bridge - (I am a beginner at electronics and have learnt everything the hard way over the last couple of months working on this design - so please be gentle with me
Anyway - to the nub of my problem. I have all the logic working to provide the logic level signals for driving the MOSFETS, but am having very little success in driving the high side.
Looking at the outputs of the logic gates which provide the switching signal to the MOSFETS on a 'scope, they seem to be switching at about 420KHz - which seems to be a lot faster than the norm (which I believe is about 20KhZ).
I have the ouputs from the logic gates going to an IR2304 half bridge driver, which I would have thought would solve my problem by providing a high enough current to drive the MOSFET gates with a floating high side drive - but it does not work - even though reading an application note from International Rectifier suggests that the IR2304 will work up to the 100's KHz frequency range.
So down to my questions :
1. Has anybody any experience they could share with me on using the IR2304 in this way?
2. The IR2304 is a "bootstrap mode" driver - I have been unable to find an explanation of what this means - can anyone help?
3. I have heard that this type of "bootstrap" driver will not work unless there is switching going on (i.e where the current is permanently switched on) - is this true?
Any help would be much appreciated. I am so close to getting everything to work and I hope this is the last hurdle.
Best Regards
Pete
I am in the process of building a biploar stepper motor driver, which uses IRF540 MOSFETS for the high and low side switching. The current limiting mechanism is based on figure 4.11 from the "!Jones on stepping motors" we page at this address : http://www.cs.uiowa.edu/~jones/step/current.html.
I say based on it, because I have a slightly different arrangement for the voltage sensing - I use an IRC540 current sensing MOSFET instead of a resistor. I also have a Microchip PIC driving 2 * DACs to provide the reference voltages for the comparators and the logic is all 4000 series with a VCC of 12v.
I originally had 4000 series chips with a Vcc of 12v driving the gates of the MOSFETs. This gave me problems because when I did the design I hadn't realised the problem of driving high side MOSFETS in a bridge - (I am a beginner at electronics and have learnt everything the hard way over the last couple of months working on this design - so please be gentle with me
Anyway - to the nub of my problem. I have all the logic working to provide the logic level signals for driving the MOSFETS, but am having very little success in driving the high side.
Looking at the outputs of the logic gates which provide the switching signal to the MOSFETS on a 'scope, they seem to be switching at about 420KHz - which seems to be a lot faster than the norm (which I believe is about 20KhZ).
I have the ouputs from the logic gates going to an IR2304 half bridge driver, which I would have thought would solve my problem by providing a high enough current to drive the MOSFET gates with a floating high side drive - but it does not work - even though reading an application note from International Rectifier suggests that the IR2304 will work up to the 100's KHz frequency range.
So down to my questions :
1. Has anybody any experience they could share with me on using the IR2304 in this way?
2. The IR2304 is a "bootstrap mode" driver - I have been unable to find an explanation of what this means - can anyone help?
3. I have heard that this type of "bootstrap" driver will not work unless there is switching going on (i.e where the current is permanently switched on) - is this true?
Any help would be much appreciated. I am so close to getting everything to work and I hope this is the last hurdle.
Best Regards
Pete