Post by thread:[EE]: Power MOSFET driver

Hello, inspired by the recent thread about "Switching low voltage AC", I'm returning to the development of a solid state relay using MOSFETs. I'm trying various configurations of MOSFET drivers, but what I really need is a schmitt trigger with some mA capabilities. A schmitt trigger can be done with an op-amp, but the slew-rate of the opamps I know can swing to GND and VCC is very slow. Any sugestions? Thank you very much, Brusque ----------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Researcher and Developer Blumenau - SC - Brazil Say NO to HTML mail http://www.citronics.com.br ----------------------------------------------------------------- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Tue, 26 Feb 2002 10:02:57 -0300, you wrote: >Hello, > > inspired by the recent thread about "Switching low voltage AC", I'm >returning to the development of a solid state relay using MOSFETs. > > I'm trying various configurations of MOSFET drivers, but what I really >need is a schmitt trigger with some mA capabilities. A schmitt trigger can >be done with an op-amp, but the slew-rate of the opamps I know can swing to >GND and VCC is very slow. > > Any sugestions? Use a comparator instead of an op-amp. op-amps do not make good comparators in many cases. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

cmos : CD4093 ttl : 7413 or equivalents comparators: LM393, LM111 discrete : two transistors The slew rate does not count too much because any schmitd trigger designed with operational amplifiers use the comparator structure ( positive feedback ) which increase the slew rate. Vasile On Tue, 26 Feb 2002, Edson Brusque wrote: {Quote hidden}> Hello, > > inspired by the recent thread about "Switching low voltage AC", I'm > returning to the development of a solid state relay using MOSFETs. > > I'm trying various configurations of MOSFET drivers, but what I really > need is a schmitt trigger with some mA capabilities. A schmitt trigger can > be done with an op-amp, but the slew-rate of the opamps I know can swing to > GND and VCC is very slow. > > Any sugestions? > > Thank you very much, > > Brusque > > ----------------------------------------------------------------- > Edson Brusque C.I.Tronics Lighting Designers Ltda > Researcher and Developer Blumenau - SC - Brazil > Say NO to HTML mail http://www.citronics.com.br > ----------------------------------------------------------------- > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hello Mike and Vasile, >Use a comparator instead of an op-amp. op-amps do not make good >comparators in many cases. what I don't like about the comparators is the open-collector outputs. As I'm implementing an auxiliary power supply with resistor-zener regulation, I have to stay low current. > cmos : CD4093 Very good sugestion! I'll this today. > ttl : 7413 or equivalents Vmm, only 5V I suppose. I need 10V minimum. > comparators: LM393, LM111 Open collector. > discrete : two transistors I've thought of using a pair of TO-92 MOSFETs (BSS100/BSS110) to implement a driver that could help to sink/source current to the high power MOSFETs gates. I've learned today that Fairchild makes some optocouplers (MOC5007/8/9) with schmitt trigger outputs that could have VCC as high as 16V. I would like to try these ones, but they're open collector too... Thank you very much, Brusque ----------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Researcher and Developer Blumenau - SC - Brazil Say NO to HTML mail http://www.citronics.com.br ----------------------------------------------------------------- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

ICL7667 http://www.intersil.com/Data/FN/FN2/FN2853/FN2853.pdf Schmitt, fast, and can also level shift from 5V to 12V. I've used it with PWM and 80A FETs, love it -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Tue, 26 Feb 2002, Edson Brusque wrote: > >Use a comparator instead of an op-amp. op-amps do not make good > >comparators in many cases. The greatest mistake that many people do, is unknowing the extraordinare advantage of an operational amplifier used as comparator against a classic open colector comparator, OA will have a smallest offset and the slew rate can be increased by supressing any lad and/or lag capacitor correction. In fact any phase correction must be avoid when OA is used as comparator. Whith this rule any fast OA become the best comparator. A good example of how to don't design a comparator is the internal f62x structure which have an offset greater than many common operationals and required some histeresys for a nice switching. best, Vasile -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Hello Jinx, > ICL7667 > www.intersil.com/Data/FN/FN2/FN2853/FN2853.pdf > Schmitt, fast, and can also level shift from 5V to 12V. I've > used it with PWM and 80A FETs, love it very interesting chip. I've requested some samples. I'm trying to find a similar chip with no-inverted output but haven't found any. Thanks, Brusque ----------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Researcher and Developer Blumenau - SC - Brazil Say NO to HTML mail http://www.citronics.com.br ----------------------------------------------------------------- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Brusque, Check out MICROCHIP's (TELCOM SEMI.) MOSFET drivers. www.microchip.com/1010/pline/analog/anicateg/power/pwrmang/mosfet/ind ex.htm I have used them before and they work very well!! Steve Steven Kosmerchock Radio Frequency Systems Phoenix, Arizona USA (WORK) http://www.rfsamericas.com http://www.geocities.com/researchtriangle/lab/6584 "Great spirits have always encountered violent oppposition from mediocre minds."--A.Einstein {Original Message removed}

> > ICL7667 > similar chip with no-inverted output but haven't found any. I never did either. I put a 74ACT132 gate (NAND Schmitt) in front of the 7667 to keep logic levels true =============================================== I've often wondered about why Schmitts are only available as inverters. If you look at the internal block diagram of a 4093 for instance you see it goes NAND >> non-inverting Schmitt >> inverter >> inverter If they left off the last inverter you'd have a non-inverting Schmitt Does anyone have an idea why they can't do this, given that the flow diagram shows a non-inverting Schmitt gate exists on the chip ? -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.