Hello, I've discovered logic-level mosfets, and am using an Arduino to drive a small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N as the power mosfet. Would a mosfet-driver be recommended to switch that mosfet on and off more quickly? Or is a logic-level mosfet already designed to efficiently turn on and off with the weak logic level signal? Thanks, Michael
mosfet driver needed for logic-level mosfets?
Started by ●May 15, 2017
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:> Hello, > > I've discovered logic-level mosfets, and am using an Arduino to drive a > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N > as the power mosfet. > > Would a mosfet-driver be recommended to switch that mosfet on and off > more quickly? Or is a logic-level mosfet already designed to > efficiently turn on and off with the weak logic level signal?You need to do some (gasp!) engineering. You need to know how quickly the FET needs to turn on and off, you need to know the FET's total gate charge, and you need to know how much current the processor pins can supply. For slow-enough PWM, no, you don't need a driver. Otherwise, yes, you do -- and you want to be careful to get a driver that has close to rail-rail output. Some of the oldy-goldie ones have bipolar drive sections with considerable (up to 1.5V) drop from supply voltage to gate drive. So -- even more engineering. -- www.wescottdesign.com
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:> Hello, > > I've discovered logic-level mosfets, and am using an Arduino to drive a > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N > as the power mosfet. > > Would a mosfet-driver be recommended to switch that mosfet on and off > more quickly? Or is a logic-level mosfet already designed to > efficiently turn on and off with the weak logic level signal?Given that you are also asking about BJT vs. FET, note that in order to switch at it's fastest, a BJT needs a base driver that can push charge in quickly and actively pull it out quickly. The difference in recovery from saturation when you pull the base below ground vs. when you just pull it _to_ ground can be dramatic. And don't use a grotty old TIP31 if you want speed -- Zetex developed some pretty impressive modern BJTs before they got bought by Diodes, Inc., and turned into a cash cow. Those transistors are still sold, and have some pretty impressive HFE_sat and VCE_sat numbers. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Reply by ●May 15, 20172017-05-15
On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:> On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: > > > Hello, > > > > I've discovered logic-level mosfets, and am using an Arduino to drive a > > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N > > as the power mosfet. > > > > Would a mosfet-driver be recommended to switch that mosfet on and off > > more quickly? Or is a logic-level mosfet already designed to > > efficiently turn on and off with the weak logic level signal? > > Given that you are also asking about BJT vs. FET, note that in order to > switch at it's fastest, a BJT needs a base driver that can push charge in > quickly and actively pull it out quickly. The difference in recovery > from saturation when you pull the base below ground vs. when you just > pull it _to_ ground can be dramatic. > > And don't use a grotty old TIP31 if you want speed -- Zetex developed > some pretty impressive modern BJTs before they got bought by Diodes, > Inc., and turned into a cash cow. Those transistors are still sold, and > have some pretty impressive HFE_sat and VCE_sat numbers. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > > I'm looking for work -- see my website!Ok, thanks for the information. You've given me lots to think about. For higher-speed switching of BJTs, you recommend yanking the base to *below* ground, then? Which EE classes are these topics discussed in? Can you recommend a book or two? Thanks, Michael
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote:>On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote: >> On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: >> >> > Hello, >> > >> > I've discovered logic-level mosfets, and am using an Arduino to drive a >> > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N >> > as the power mosfet. >> > >> > Would a mosfet-driver be recommended to switch that mosfet on and off >> > more quickly? Or is a logic-level mosfet already designed to >> > efficiently turn on and off with the weak logic level signal? >> >> Given that you are also asking about BJT vs. FET, note that in order to >> switch at it's fastest, a BJT needs a base driver that can push charge in >> quickly and actively pull it out quickly. The difference in recovery >> from saturation when you pull the base below ground vs. when you just >> pull it _to_ ground can be dramatic. >> >> And don't use a grotty old TIP31 if you want speed -- Zetex developed >> some pretty impressive modern BJTs before they got bought by Diodes, >> Inc., and turned into a cash cow. Those transistors are still sold, and >> have some pretty impressive HFE_sat and VCE_sat numbers. >> >> -- >> >> Tim Wescott >> Wescott Design Services >> http://www.wescottdesign.com >> >> I'm looking for work -- see my website! > > >Ok, thanks for the information. You've given me lots to think about. > >For higher-speed switching of BJTs, you recommend yanking the base to *below* ground, then?Yes. But not too far... ~3V maximum to avoid VBE breakdown.> >Which EE classes are these topics discussed in? Can you recommend a book or two? > >Thanks, > >Michael...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Thinking outside the box... producing elegant solutions. "It is not in doing what you like, but in liking what you do that is the secret of happiness." -James Barrie
Reply by ●May 15, 20172017-05-15
On Monday, May 15, 2017 at 11:58:39 AM UTC-7, Jim Thompson wrote:> On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote: > > >On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote: > >> On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: > >> > >> > Hello, > >> > > >> > I've discovered logic-level mosfets, and am using an Arduino to drive a > >> > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N > >> > as the power mosfet. > >> > > >> > Would a mosfet-driver be recommended to switch that mosfet on and off > >> > more quickly? Or is a logic-level mosfet already designed to > >> > efficiently turn on and off with the weak logic level signal? > >> > >> Given that you are also asking about BJT vs. FET, note that in order to > >> switch at it's fastest, a BJT needs a base driver that can push charge in > >> quickly and actively pull it out quickly. The difference in recovery > >> from saturation when you pull the base below ground vs. when you just > >> pull it _to_ ground can be dramatic. > >> > >> And don't use a grotty old TIP31 if you want speed -- Zetex developed > >> some pretty impressive modern BJTs before they got bought by Diodes, > >> Inc., and turned into a cash cow. Those transistors are still sold, and > >> have some pretty impressive HFE_sat and VCE_sat numbers. > >> > >> -- > >> > >> Tim Wescott > >> Wescott Design Services > >> http://www.wescottdesign.com > >> > >> I'm looking for work -- see my website! > > > > > >Ok, thanks for the information. You've given me lots to think about. > > > >For higher-speed switching of BJTs, you recommend yanking the base to *below* ground, then? > > Yes. But not too far... ~3V maximum to avoid VBE breakdown.Oh cool. Thanks. Michael
Reply by ●May 16, 20172017-05-16
On Mon, 15 May 2017 11:58:31 -0700, Jim Thompson wrote:> On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote: > >>On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote: >>> On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: >>> >>> > Hello, >>> > >>> > I've discovered logic-level mosfets, and am using an Arduino to >>> > drive a small 12VDC (about an amp or so) pump motor with PWM, using >>> > an IRLZ34N as the power mosfet. >>> > >>> > Would a mosfet-driver be recommended to switch that mosfet on and >>> > off more quickly? Or is a logic-level mosfet already designed to >>> > efficiently turn on and off with the weak logic level signal? >>> >>> Given that you are also asking about BJT vs. FET, note that in order >>> to switch at it's fastest, a BJT needs a base driver that can push >>> charge in quickly and actively pull it out quickly. The difference in >>> recovery from saturation when you pull the base below ground vs. when >>> you just pull it _to_ ground can be dramatic. >>> >>> And don't use a grotty old TIP31 if you want speed -- Zetex developed >>> some pretty impressive modern BJTs before they got bought by Diodes, >>> Inc., and turned into a cash cow. Those transistors are still sold, >>> and have some pretty impressive HFE_sat and VCE_sat numbers. >>> >>> -- >>> >>> Tim Wescott Wescott Design Services http://www.wescottdesign.com >>> >>> I'm looking for work -- see my website! >> >> >>Ok, thanks for the information. You've given me lots to think about. >> >>For higher-speed switching of BJTs, you recommend yanking the base to >>*below* ground, then? > > Yes. But not too far... ~3V maximum to avoid VBE breakdown.Yea verily.>>Which EE classes are these topics discussed in? Can you recommend a >>book or two?None that I know of, and no, in that order. That doesn't mean that someone else may be more helpful -- just that I don't know. I learned the technique from Zetex applications notes about 20 years ago; I used it in a prototype and never used it again. You can get a nicely controlled negative-going spike at the leading edge of your base drive with an RC network from your driver, or, if you want nice behavior over a wider range of duty cycles, a resistor-diode-cap network. It's all complercated and I can't remember the details and by God I hope there are still app notes floating around. The basic idea is that if you just pull the base to ground then the residual charges that are in the base making it conduct have to recombine, and you have to wait. If you yank them out by force then -- they're not there any more. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Reply by ●May 16, 20172017-05-16
On Mon, 15 May 2017 12:02:39 -0700 (PDT), mrdarrett@gmail.com wrote:>On Monday, May 15, 2017 at 11:58:39 AM UTC-7, Jim Thompson wrote: >> On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote: >> >> >On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote: >> >> On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: >> >> >> >> > Hello, >> >> > >> >> > I've discovered logic-level mosfets, and am using an Arduino to drive a >> >> > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N >> >> > as the power mosfet. >> >> > >> >> > Would a mosfet-driver be recommended to switch that mosfet on and off >> >> > more quickly? Or is a logic-level mosfet already designed to >> >> > efficiently turn on and off with the weak logic level signal? >> >> >> >> Given that you are also asking about BJT vs. FET, note that in order to >> >> switch at it's fastest, a BJT needs a base driver that can push charge in >> >> quickly and actively pull it out quickly. The difference in recovery >> >> from saturation when you pull the base below ground vs. when you just >> >> pull it _to_ ground can be dramatic. >> >> >> >> And don't use a grotty old TIP31 if you want speed -- Zetex developed >> >> some pretty impressive modern BJTs before they got bought by Diodes, >> >> Inc., and turned into a cash cow. Those transistors are still sold, and >> >> have some pretty impressive HFE_sat and VCE_sat numbers. >> >> >> >> -- >> >> >> >> Tim Wescott >> >> Wescott Design Services >> >> http://www.wescottdesign.com >> >> >> >> I'm looking for work -- see my website! >> > >> > >> >Ok, thanks for the information. You've given me lots to think about. >> > >> >For higher-speed switching of BJTs, you recommend yanking the base to *below* ground, then? >> >> Yes. But not too far... ~3V maximum to avoid VBE breakdown. > > >Oh cool. Thanks. > >Michaelcircuit is something called the Baker clamp https://en.wikipedia.org/wiki/Baker_clamp
Reply by ●May 16, 20172017-05-16
On Monday, May 15, 2017 at 2:33:12 PM UTC-4, mrda...@gmail.com wrote:> On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote: > > On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: > > > > > Hello, > > > > > > I've discovered logic-level mosfets, and am using an Arduino to drive a > > > small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N > > > as the power mosfet. > > > > > > Would a mosfet-driver be recommended to switch that mosfet on and off > > > more quickly? Or is a logic-level mosfet already designed to > > > efficiently turn on and off with the weak logic level signal? > > > > Given that you are also asking about BJT vs. FET, note that in order to > > switch at it's fastest, a BJT needs a base driver that can push charge in > > quickly and actively pull it out quickly. The difference in recovery > > from saturation when you pull the base below ground vs. when you just > > pull it _to_ ground can be dramatic. > > > > And don't use a grotty old TIP31 if you want speed -- Zetex developed > > some pretty impressive modern BJTs before they got bought by Diodes, > > Inc., and turned into a cash cow. Those transistors are still sold, and > > have some pretty impressive HFE_sat and VCE_sat numbers. > > > > -- > > > > Tim Wescott > > Wescott Design Services > > http://www.wescottdesign.com > > > > I'm looking for work -- see my website! > > > Ok, thanks for the information. You've given me lots to think about. > > For higher-speed switching of BJTs, you recommend yanking the base to *below* ground, then? > > Which EE classes are these topics discussed in? Can you recommend a book or two?"Practical Electronics for Inventors" is a good basic electronics book, (and the price is right.) after that go to AoE3. George H.> > Thanks, > > Michael
Reply by ●May 16, 20172017-05-16
On Monday, May 15, 2017 at 9:59:54 PM UTC-7, Tim Wescott wrote:> On Mon, 15 May 2017 11:58:31 -0700, Jim Thompson wrote: > > > On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote: > > > >>On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote: > >>> On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote: > >>> > >>> > Hello, > >>> > > >>> > I've discovered logic-level mosfets, and am using an Arduino to > >>> > drive a small 12VDC (about an amp or so) pump motor with PWM, using > >>> > an IRLZ34N as the power mosfet. > >>> > > >>> > Would a mosfet-driver be recommended to switch that mosfet on and > >>> > off more quickly? Or is a logic-level mosfet already designed to > >>> > efficiently turn on and off with the weak logic level signal? > >>> > >>> Given that you are also asking about BJT vs. FET, note that in order > >>> to switch at it's fastest, a BJT needs a base driver that can push > >>> charge in quickly and actively pull it out quickly. The difference in > >>> recovery from saturation when you pull the base below ground vs. when > >>> you just pull it _to_ ground can be dramatic. > >>> > >>> And don't use a grotty old TIP31 if you want speed -- Zetex developed > >>> some pretty impressive modern BJTs before they got bought by Diodes, > >>> Inc., and turned into a cash cow. Those transistors are still sold, > >>> and have some pretty impressive HFE_sat and VCE_sat numbers. > >>> > >>> -- > >>> > >>> Tim Wescott Wescott Design Services http://www.wescottdesign.com > >>> > >>> I'm looking for work -- see my website! > >> > >> > >>Ok, thanks for the information. You've given me lots to think about. > >> > >>For higher-speed switching of BJTs, you recommend yanking the base to > >>*below* ground, then? > > > > Yes. But not too far... ~3V maximum to avoid VBE breakdown. > > Yea verily. > > >>Which EE classes are these topics discussed in? Can you recommend a > >>book or two? > > None that I know of, and no, in that order. That doesn't mean that > someone else may be more helpful -- just that I don't know. > > I learned the technique from Zetex applications notes about 20 years ago; > I used it in a prototype and never used it again. > > You can get a nicely controlled negative-going spike at the leading edge > of your base drive with an RC network from your driver, or, if you want > nice behavior over a wider range of duty cycles, a resistor-diode-cap > network. It's all complercated and I can't remember the details and by > God I hope there are still app notes floating around. > > The basic idea is that if you just pull the base to ground then the > residual charges that are in the base making it conduct have to > recombine, and you have to wait. If you yank them out by force then -- > they're not there any more. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > > I'm looking for work -- see my website!Huh. I have to check out Zetex. Thanks. You might have to write another book! I took a peek at your Controls book and I had no idea Scilab was free. A free Matlab clone, huh? Michael
