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I used to be an industry expert on MOSFET/IGBT a long time ago [...]I could design one pretty fast but gone are the days of discrete electronics that I used to design the bootstrapped drivers of the top 2 n-channel MOSFETs of the H-bridge.
I searched eBay hoping to get to an IC based full H-Driver but could only get to A3986SLDT and this thing is kind of overpriced. I will appreciate if someone can suggest a cheaper alternative. Thanks!!
I completely agree that many pros use p-channel BJTs for H-bridges because that is a simple and proven solution.
I understand all the advantages of doing that but with p and n channel BJTs efficient utilization of a 6V system can be ruled out.
eBay is not and probably never be the source of parts for pros but whenever I do a generic search on data sheets and application notes for a H-bridge driver, I am stuck with useless crap on websites like datasheetcatalog, alldatasheet, datasheetarchive besides others (5 years ago I remember hitting much better info on Google but it is not that simple any more I believe) so had tried a few searches on eBay that did seem to get me somewhere - I therefore welcome any suggestions in this regard.
This is a relatively inexpensive motor driver that does not use darlington pair transitors. I still do not like it since it uses p-channel MOSFETs not the best of design decisions. I will keep looking and updating improved versions as I am able to find/design them....
IN4001 diodes shown in the design are kind of hillarious to me for they are not fast recovery schottkey ones... these can be dropped since MOSFETs come with a built in free-wheeling diode...
there are design flaws but the idea is very workable.
Other one I noticed is that the zener is 15V but the regulated voltage that they produce is 12V.....!!
About the perception of a transistor, any 3 terminal device that transfers resistance is a transistor but the similarity ends there. MOSFET and IGBT are much more sensitive (especially for static electricity), have a positive temperature coeffecient and international rectifiers made them into Hexagonal structures calling them Hexfets to be able to reduce Rds to the level of milliohms. MOSFETs can pack 10s of watts into a TO-220 pack compared to a few watts by BjTs. BjTs always drop a good fraction of a volt as Vce at saturation for currents ranging a few amperes, this can be anywhere from 0.2-0.5V as discussed above. Transistors are generally slow and Cbe for a BjT is not as significant as the Cgs of a MOSFET (terminologies hold good for n-channel/n-p-n). Additionally while MOSFET is a voltage device (cos Igs = 0, transistor is primarily a current device, and therefore gain is measured in terms of current in the former, it is measured in terms of voltage gain for MOSFETs)So to the untrained eye, a MOSFET in a typical TO-220 pack will look the same as a darlington in the same package.... but for a good designer that similarity ends with PCB layout design. Even the heat sink design in terms of degree kelvin/watt is different for both.So while a hobbist buys the standard products and puts them together, a designer has to look more from the first principles. I realize that there has been a lot of talk and no real work on this thread.... however if someone is keen on making a point, they are more than welcome to comment on alternatives like the thyristors or SCRs, full and half H-bridge, synchronous and asynchronous commutation techniques instead of merely the 'spell checks' and probably also reduce the 'muscle flex'. I do not say that out of rage but because i have seen that individual provide great advice on this and other threads and also get a just a bit emotional which has no place in robotics since a robot with emotions has not been created as yet
I think we discuss only technical here-ambcorp- you should take out the "expert" thing- that is the only fault I see- if you are expert give more help-soren- your comments means no one talk like their mind- they should first think... what will soren think? Oh I am afraid this is not like by soren- soren if you have this problem please stop answering all question. Not only this one here...
I am new but I will talk what my mind think not what other member want me think-