H-Bridge high side floating supply

[niclatrique]

I'm in the process of designing my first DIY stepper driver. I plan tu use IR2104 with N-channel fets(IRF540). The thing is, I need a floating power supply to provide a continous 12V higher than the supply voltage to continously drive the high side. I've seen AN-978 from IRFhttp://www.irf.com/technical-info/appnotes/an-978.pdf on page 13 it shows a 555 timer arranged as voltage doubler. A zener/resistor is used as a floating supply for the 555. I would like to find a better way to provide a floating supply of 12V like the zener/resistor network does but with a higher efficiency and current capabality.

If someone has an idea...

Thanks

Nic

[NC Cams]

IR has a high side fet driver that includes its own charge pump. Perfect for driving the high side fets in an H bridge, especially if you use logic level fets - they run fine at Vgs=10vdc..

TI had some small switch mode power supply (SMPS) IC's (TL482 or 483 something like that) at one time which would do what you ask - however, the 555 doubler is much cheaper and easier to come by.

This IC was used in a lot of the mosfet style electronic speed controls that were the vogue in R/C cars and such. You could easily generate 12 or even 20vdc with it based on the divider network that you used.

[niclatrique]

Well, the IR2104 has a high side built in driver which is good for voltages up to 600V but that principle of charge pump works fine under constant on/off cycles of the power fet. If I keep the high side fet switched on for a long period of time, the capacitor cannot sustain the gate current for an indefinite time.

My real problem is how do I overcome this problem ?

Any suggstion ?

thanks

Nic

[pastera]

You can use an isolated DC/DC converter but it's going to cost a lot more than a 555 and a few discretes!

Do you have other components you want to power or are you concerned you will have issues?

As far as use in a stepper driver, if the supply voltage is higher than the rated voltage the normal chopping action will recharge the bootstrap. If the motor is spinning fast enough not to chop, normal commutation will cause a recharge of the bootstrap.

Aaron

[niclatrique]

Thanks Pastera,

This is what was beginning of thinking. I'll try it out with a L297 first to see how it works without the 555 and the fet driver connected to my scope I'll how it goes.

thanks

[Mariss Freimanis]

The IR2104S top-side MOSFET gate drive power supply uses what's called a boot-strap circuit. Advantage is a very fast response, disadvantage is it does leak-off to being useless in less than a second.

A charge-pump circuit uses an oscillator driving a DC isolation capacitor that gets rectified to produce a DC voltage. Advantage is a continuous DC voltage, disadvantage is a very slow response time.

You will need both circuits, boot-strap and charge-pump to do what you need. This gets a little complex. Think real about your circuit and see if it can't afford a 95% duty-cycle to let just a boot-strap circuit do the work.

Mariss