H Bridge, NMOS AND PMOS DRIVER
in [Design]
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From: JosephKK on 12 Aug 2010 23:26 On Thu, 5 Aug 2010 17:33:56 -0700 (PDT), sarah kent <sarah6541(a)gmail.com> wrote: >On Aug 5, 7:09�pm, "Tim Williams" <tmoran...(a)charter.net> wrote: >> "sarah kent" <sarah6...(a)gmail.com> wrote in message >> >> news:afad00db-3e31-493f-bd1e-7650e7abae39(a)k19g2000yqc.googlegroups.com... >> >> > Hello All, >> >> > I am tring to generate a square wave of 100KHz and 200 volts peak to ^^^^^^ >> > peak across a resistor via H- bridge. The current could go upto 30A. >> >> AC only, no DC? �Variable duty cycle? �If so, what kind (balanced ala >> TL494 or differential ala class D audio)? >> >> Especially if the supply is line-operated (maybe this won't be an option >> for your load, I don't have a clue), I like to drive AC-only, balanced-PWM >> loads with a gate drive transformer. �This can be driven directly from a >> TL598 (or UC3525, or...), or your choice of gate driver (as long as it's >> not a complementary emitter follower type). >> >> > I am looking into two following ways to drive the NMOS ( four NMOS >> > transistors ) H - bridge. >> >> > 1. >> >> > a. Using H bridge Drivers HIP4081A. I tried to look for the >> > replacement of HIP4081A but only found A4940 from Allegro microsystems >> > which a little slower than the HIP part regarding rise and fall time. >> >> Do you have a spec for how fast you need to run? �100ns is fine at 100kHz, >> you'll most likely burn more power in conduction than switching. �Anything >> faster is a bonus, but not particularly useful (and could be dangerous, >> due to higher dI/dt forcing improved layout!). >> >> > According to my understanding the Driver chip has to charge the input >> > capacitance of the transistors. I am planning to use NMOS transistor >> > (IRF540). >> >> Whaaa? �Did you read the Vds(max) on that!? �200Vp-p needs a 100V power >> supply. �That means >150V transistors! >> >> > So, according to HIP 4081A data sheet trise = 10nsec at C= 1000pF and >> > if power supply = 50Volts (60% of 50V = 30volts) �, So, I calculated >> > (1000pF x 30V) / 10nsec = 3 Amp. >> >> > The gate to source charging capacitance of IRF540 is 14nC; So, the >> > charging time would be >> >> > (14nC x 30 V) / 3 = 140nsecs. Are my calculations accurate and in >> > right direction? >> >> No, C == A.s, so 14nAs * 30V = 420nVAs == nJ (energy). �Divide by amps >> gets you Vs, which is flux, not time. >> >> Since C == A.s, 14nC / 3A = 4.67ns. �This is less than the rated t_r so it >> will be chip-limited, not capacitance-limited. >> >> > Which proves that the A4940 is a slower part. But how will it effect >> > the voltage waveform across the resistive load. I meant to say what >> > would be the difference between the two waveforms generated by two >> > different driver chips. >> >> Likely the HIP is faster. �You'd use it if you needed to drive >> particularly large FETs particularly fast. �If you don't need the speed, >> don't put down the money for it. �A regular IR2112 is enough for mere >> IRF540s at 100kHz. �Well, a little sluggish for 100k, more like 50k for >> best results, but still not bad. >> >> > 2. The second method is to use four NPN transitors to drive two PMOS >> > transistors (High side) and two NMOS (Low Side) transistors. >> >> No. �Check Vgs(max). �Complementary MOS is impossible over 20V supply >> without extra circuitry, which adds enough complexity that you are better >> off with a driver chip and NMOS (which work better anyway). >> >> > Microcontroller will provide the PWM pulses to control the 2N2222 >> > transistors. You can find the diagram at the following link. >> >> >http://a.imageshack.us/img39/3520/201115.jpg >> >> > I am thinking of using 2N2222A to drive two (IRF540N) but unable to >> > find the PMOS equivalent of IRF540 N. Any suggestions!! Do I need them >> > of the same ratings? >> >> > Please also suggest that H - bridge driver approach is the better >> > approach or the NPN transistors driving the PMOS and NMOS transistors >> > is the good approach. I heard that the NPN driving the PMOS and NMOS >> > is the most efficient way, if yes than how? >> >> > Would 2N222 be able to charge the MOSFETS quickly as HIP4081A. >> >> Nope: >> >> 2N222 >> Low Power, General Purpose, Ge, PNP, 70mW, 15V, 12V, 70mA, 85>C, 400KHz, >> 70, 20T, RCA, TO1 >> >> Neato, it's germanium, 400kHz fT. �:^) >> >> Typoes aside, forget 2N2222 anyway. �Like 2N3055 and LM741, it is ancient >> and best left forgotten, thrown to the gutter, on the road of progress. >> 2N4401/03 are quite reasonable substitutes, and there are numerous others >> with even better performance if you insist on rolling your own gate drive. >> ZTX651 comes to mind, it's even smaller than 2N4401 yet drives 3A peak >> quite easily. �TC4420 and similar are quite popular for big jobs (6A peak, >> good for monster IGBTs). >> >> Tim >> >> -- >> Deep Friar: a very philosophical monk. >> Website:http://webpages.charter.net/dawill/tmoranwms > >Hi, > >Thanks for the reply. > >I have following questions > >1. Why complementary MOSFET scheme can not work with power supply >greater than 20 Volts? >2. Is there a way that I can generate the sine wave of 200 volts peak ^^^^ >to peak at 100KHz with out using H bridge driver or four MOSFETS? > > >Sarah Whoa. What is up with changing the target? At first you wanted a square wave at 100 kHz, now you want a sine wave? Completely different problem. |