Is it even possible? How can it be achieved? I built an H bridge using 4 NPN IRF520 transistors but my multimeter reads 2.2v even though the power supply is a 9v battery !
I would be very grateful if you could help me
Thanks.
Is it even possible? How can it be achieved? I built an H bridge using 4 NPN IRF520 transistors but my multimeter reads 2.2v even though the power supply is a 9v battery !
I would be very grateful if you could help me
Thanks.
I have not seen any working H-Bridge when the high-side and low-side transistors were all NPN or PNP. I think you need PNP on the high side and NPN on the low side.
See:
See particularly articles 7, 8 and 12 about low-side and high-side switching.
I'd agree for bipolar... For MOSFET H-bridges all-n-channel is common however, but special circuitry is in place to generate gate voltages
higher than the supply for the top MOSFETS.
Here's a bipolar H-bridge suggestion:
This actual circuit I've used with surface mount NPN/PNP superbeta transistor pairs for the switches, which
have very low Vsat, and a clever trick of using a small surface mount bridge rectifier to provide all 4
free-wheeling diodes in one go.
You must be careful not to drive both inputs high at the same time! Some means of monitoring over-current
would be a wise addition.
Is it even possible?
Yes. Pretty much any combination of PNP/NPN can be made to work.
IRF520 is an n-channel mosfet, not an npn transistor.
dc42:
IRF520 is an n-channel mosfet, not an npn transistor.
Fine, but how does that make any difference? Can I build my own h bridge using 4 IRF520? Maybe using two of these and two transistors?
It appears that an h bridge can be built because I actually have done so, the problem is that there is a considerable voltage drop that would cause heat and energy waste so it definitely is not the way to go.
Can I build my own h bridge using 4 IRF520? Maybe using two of these and two transistors?
I think h-bridges using all NPN MOSFETs use a bootstrap circuit to keep the upstream MOSFET gate voltage higher than the h-bridge supply voltage. If you are thinking of making a DIY MOSFET h-bridge, then the below discussion might be of interest to you. Lots of inexpensive h-bridges now on ebay.
also I don't think IRF 520 is even logic level
dhenry:
Is it even possible?
Yes. Pretty much any combination of PNP/NPN can be made to work.
I, for one, would be interested in seeing an All NPN H-Bridge circuit. Can you point to one or draw one?
Below is a bootstrap setup for a high side MOSFET.
zoomkat:
Below is a bootstrap setup for a high side MOSFET.
Note that that bootstrap circuit imposes two restrictions on the H-bridge: