On 28 Sep 2019 01:57:35 -0700, Winfield Hill <winfieldhill@yahoo.com> wrote:>John Larkin wrote... >> >> On 27 Sep 2019, bloggs.fredbloggs.fred@gmail.com wrote: >>> On September 26, 2019, John Larkin wrote: >>>> >>>> I have a 48 volt power supply and I want to drive a >>>> lot of relays and uPs and FPGAs and stuff, so I >>>> figured I'd knock it down to 12 volts first. >>> >>> Isn't that 12V TVS cutting things close? >> >> A 12 volt TVS doesn't conduct at 12 volts. More like 14. >> >> If the reg fails, it would push 48 volts into 7 PC boards >> that are all expecting 12. I could include the TVS and >> maybe an 0805 series resistor as sacrifial parts, to >> localize the flames. > > To protect those parts, use an SCR shutdown with a fuse.Wow, I haven't done a crowbar in decades. It used to be popular. In theory, a crowbar SCR needs a fancy gate driver chip, not just a zener into the gate. I'm assuming that a hunky (600 watt) TVS will fail hard shorted, enough to take out a resistor in the 48V switcher input. If I use a crowbar and a fuse, it will have to come home as an RMA anyhow, if the fuse blows. (I should test some 1 ohm 0805 resistors for their behavior as fuses. I can use my exploder rig. May as well blow up some TVSs too... see how much energy it takes to open them up.) We've had bad experiences with surface-mount fuses, so if we crowbar we'd go with an MDL 5mm or 3AG in a socket on the board. The switcher failure would be a low probability event, so protecting against over-voltage on the 12 volt rail is purely optional. If a box fails, it will come back for repair and the control board (where the 48-12 switcher lives) will need to be repaired. The TVS would just limit damage downstream, especially on the other 6 boards that get the shared +12. We don't usually over-voltage protect the smaller switchers, like the 3.3 and 1 volt supplies. We do check their output voltages. -- John Larkin Highland Technology, Inc lunatic fringe electronics
stonehenge regulator
Started by ●September 26, 2019
Reply by ●September 28, 20192019-09-28
Reply by ●September 28, 20192019-09-28
jlarkin@highlandsniptechnology.com wrote...> > We've had bad experiences with surface-mount fuses, so if we > crowbar we'd go with an MDL 5mm or 3AG in a socket on the board.The idea of an SCR is to create really high fault currents, so an appropriate low-value 0805 resistor should blow out. If your input is fused, ideally the resistor would go first. The customer could make a repair, if they were brave enough.> ... The TVS would just limit damage downstream ...Exactly, my worry is the TVS, with its very high dissipation, could fail. Maybe it would fail shorted, but maybe not. An SCR running at 1V is safer. If you really want to be safe, use the serious fail-safe circuit Paul devised: https://www.dropbox.com/s/a33pelolwzrdv37/9x.7_crowbar.pdf?dl=1 -- Thanks, - Win
Reply by ●September 28, 20192019-09-28
On 28 Sep 2019 09:24:38 -0700, Winfield Hill <winfieldhill@yahoo.com> wrote:>jlarkin@highlandsniptechnology.com wrote... >> >> We've had bad experiences with surface-mount fuses, so if we >> crowbar we'd go with an MDL 5mm or 3AG in a socket on the board. > > The idea of an SCR is to create really high fault currents, > so an appropriate low-value 0805 resistor should blow out. > If your input is fused, ideally the resistor would go first. > The customer could make a repair, if they were brave enough. > >> ... The TVS would just limit damage downstream ... > > Exactly, my worry is the TVS, with its very high dissipation, > could fail. Maybe it would fail shorted, but maybe not. An > SCR running at 1V is safer. If you really want to be safe, > use the serious fail-safe circuit Paul devised: > >https://www.dropbox.com/s/a33pelolwzrdv37/9x.7_crowbar.pdf?dl=1Way too complex to protect against a low-probability event. I was just explaining to the kids that life is risky. It doesn't make sense to add weeks or months of engineering to reduce risk a tiny amount. Done is better than perfect. Done can be sold. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 28, 20192019-09-28
jlarkin@highlandsniptechnology.com wrote...> > On 28 Sep 2019, Winfield Hill wrote: > >>> ... The TVS would just limit damage downstream ... >> >> Exactly, my worry is the TVS, with its very high dissipation, >> could fail. Maybe it would fail shorted, but maybe not. An >> SCR running at 1V is safer. If you really want to be safe, >> use the serious fail-safe circuit Paul devised: >> >>https://www.dropbox.com/s/a33pelolwzrdv37/9x.7_crowbar.pdf?dl=1 > > Way too complex to protect against a low-probability event.It was protecting $8k of electronic PCBs. I thought the impact in your case would be pretty dramatic as well. A portion of the circuit might be sufficient. -- Thanks, - Win
Reply by ●September 28, 20192019-09-28
On Saturday, September 28, 2019 at 1:57:03 PM UTC-4, Winfield Hill wrote:> jlarkin@highlandsniptechnology.com wrote...> > On 28 Sep 2019, Winfield Hill wrote:> >>> ... The TVS would just limit damage downstream ...> >> Exactly, my worry is the TVS, with its very high dissipation, > >> could fail. Maybe it would fail shorted, but maybe not. An > >> SCR running at 1V is safer. If you really want to be safe, > >> use the serious fail-safe circuit Paul devised:> >>https://www.dropbox.com/s/a33pelolwzrdv37/9x.7_crowbar.pdf?dl=1> > Way too complex to protect against a low-probability event.> It was protecting $8k of electronic PCBs. I thought > the impact in your case would be pretty dramatic as > well. A portion of the circuit might be sufficient.> Thanks, > - WinHere's a much simpler method. Replace the switch with a TL431. Watch the wrap. Version 4 SHEET 1 1608 1700 WIRE 624 -208 -80 -208 WIRE 880 -208 624 -208 WIRE 880 -160 880 -208 WIRE 624 -144 624 -208 WIRE 768 -144 720 -144 WIRE 816 -144 768 -144 WIRE 832 -144 816 -144 WIRE 768 -80 768 -144 WIRE -80 -48 -80 -208 WIRE -32 -48 -80 -48 WIRE 112 -48 -32 -48 WIRE 176 -48 112 -48 WIRE 320 -48 256 -48 WIRE 384 -48 320 -48 WIRE 464 -48 384 -48 WIRE 608 -48 544 -48 WIRE 672 -48 672 -80 WIRE 672 -48 608 -48 WIRE -80 -32 -80 -48 WIRE 112 -32 112 -48 WIRE 880 -32 880 -64 WIRE 960 -32 880 -32 WIRE 976 -32 960 -32 WIRE 880 0 880 -32 WIRE 768 16 768 0 WIRE 320 48 320 -48 WIRE -80 64 -80 48 WIRE 112 64 112 48 WIRE 208 64 112 64 WIRE 272 64 208 64 WIRE 112 96 112 64 WIRE 880 96 880 80 WIRE 272 112 256 112 WIRE 256 128 256 112 WIRE 112 192 112 176 WIRE 320 192 320 128 FLAG -80 64 0 FLAG 320 192 0 FLAG -32 -48 Vin FLAG 112 192 0 FLAG 608 -48 Q1B FLAG 768 16 0 FLAG 880 96 0 FLAG 816 -144 M1G FLAG 960 -32 Vout FLAG 256 128 0 FLAG 208 64 R1R3 FLAG 384 -48 R2R4 SYMBOL voltage -80 -48 R0 WINDOW 39 0 0 Left 2 WINDOW 3 -54 150 Left 2 SYMATTR Value PULSE(0 50 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 160 -32 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 96 -48 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 96 80 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 720 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 89 64 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N5401 SYMBOL res 560 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 832 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 752 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 864 -16 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 320 144 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 TEXT 128 -288 Left 2 !.tran 0 1m 0 1u TEXT 128 -320 Left 2 ;'Overvoltage Protection TEXT 72 288 Left 2 !.model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=100 Bf=132.1 Ne=1.375 \n+Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 Nc=2 Isc=0 Ikr=0 Rc=1.6 Cjc=17.63p \n+Mjc=.5312 Vjc=.75 Fc=.5 Cje=73.39p Mje=.3777 Vje=.75 Tr=1.476n Tf=641.9p \n+Itf=0 Vtf=0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild) TEXT 72 424 Left 2 !.model Si7489DP VDMOS(Rg=3 Rd=31.2m Rs=1m Vto=-2.4 mtriode=2.2 Kp=35 \n+lambda=0.1 Cgdmax=6n Cgdmin=10p A=1 Cgs=4n cjo=200p M=.3 VJ=.9 Is=3.6p \n+Rb=5.5m mfg=Siliconix ksubthres=.1 Vds=-100 Ron=34m Qg=106n pchan) TEXT 72 248 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0)
Reply by ●September 28, 20192019-09-28
On Saturday, September 28, 2019 at 12:24:56 PM UTC-4, Winfield Hill wrote:> jlarkin@highlandsniptechnology.com wrote... > > > > We've had bad experiences with surface-mount fuses, so if we > > crowbar we'd go with an MDL 5mm or 3AG in a socket on the board. > > The idea of an SCR is to create really high fault currents, > so an appropriate low-value 0805 resistor should blow out. > If your input is fused, ideally the resistor would go first. > The customer could make a repair, if they were brave enough. > > > ... The TVS would just limit damage downstream ... > > Exactly, my worry is the TVS, with its very high dissipation, > could fail. Maybe it would fail shorted, but maybe not. An > SCR running at 1V is safer. If you really want to be safe, > use the serious fail-safe circuit Paul devised: > > https://www.dropbox.com/s/a33pelolwzrdv37/9x.7_crowbar.pdf?dl=1It gets even more complicated when you have a bipolar supply and the load is damaged if the supply goes out of balance. Last one I did used the Motorola MC3423 self- contained overvoltage sense and SCR driver, which is about as complicated as your circuit. IIRC the application literature of the time stressed care must be taken to ensure the duration of the gate drive gets past the I2t threshold of activating the protection device. For the mechanical stuff like breakers and fuses, you need something like 100x peak overcurrent or more to get the trip in us-ms time frame, and that can't always happen. If that can't happen, then you need to stretch the t in the I2t via the gate drive. Looks like it's still available from Rochester. https://www.onsemi.com/pub/Collateral/MC3423-D.PDF Dunno if they upgraded to a better IC or someone else came in and stole their business.> > > -- > Thanks, > - Win
Reply by ●September 28, 20192019-09-28
On Friday, September 27, 2019 at 5:29:33 PM UTC-4, John Larkin wrote:> On Fri, 27 Sep 2019 13:47:45 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Thursday, September 26, 2019 at 5:56:15 PM UTC-4, John Larkin wrote: > >> I have a 48 volt power supply and I want to drive a lot of relays and > >> uPs and FPGAs and stuff, so I figured I'd knock it down to 12 volts > >> first. > >> > >> We have LM2567HV-ADJ in stock, a 52 KHz Simple Switcher probably > >> designed by druids during the last ice age. Figured I'd breadboard the > >> reg just for fun. A boy gets tired of typing all day. > >> > >> https://www.dropbox.com/sh/ajtqs7c1nswfhey/AABi7r0gchljjrxka4aHZItfa?dl=0 > >> > >> > >> Works pretty well, actually. Nothing gets very warm at 1 amp out. > >> > >> Yes, that unshielded drum core will spray field everywhere, but then I > >> am simulating alternators. > > > >Isn't that 12V TVS cutting things close? > > A 12 volt TVS doesn't conduct at 12 volts. More like 14. > > If the reg fails, it would push 48 volts into 7 PC boards that are all > expecting 12. I could include the TVS and maybe an 0805 series > resistor as sacrifial parts, to localize the flames.LOL- localize the flames.... I wonder with your hefty relay drive, how the switcher responds to a sudden discontinuation of current loading. Will the series inductor overvoltage for a while conducting through the TVS? I think so. That would be worth running through a sim.
Reply by ●September 28, 20192019-09-28
On Sat, 28 Sep 2019 14:53:01 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Friday, September 27, 2019 at 5:29:33 PM UTC-4, John Larkin wrote: >> On Fri, 27 Sep 2019 13:47:45 -0700 (PDT), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >> >On Thursday, September 26, 2019 at 5:56:15 PM UTC-4, John Larkin wrote: >> >> I have a 48 volt power supply and I want to drive a lot of relays and >> >> uPs and FPGAs and stuff, so I figured I'd knock it down to 12 volts >> >> first. >> >> >> >> We have LM2567HV-ADJ in stock, a 52 KHz Simple Switcher probably >> >> designed by druids during the last ice age. Figured I'd breadboard the >> >> reg just for fun. A boy gets tired of typing all day. >> >> >> >> https://www.dropbox.com/sh/ajtqs7c1nswfhey/AABi7r0gchljjrxka4aHZItfa?dl=0 >> >> >> >> >> >> Works pretty well, actually. Nothing gets very warm at 1 amp out. >> >> >> >> Yes, that unshielded drum core will spray field everywhere, but then I >> >> am simulating alternators. >> > >> >Isn't that 12V TVS cutting things close? >> >> A 12 volt TVS doesn't conduct at 12 volts. More like 14. >> >> If the reg fails, it would push 48 volts into 7 PC boards that are all >> expecting 12. I could include the TVS and maybe an 0805 series >> resistor as sacrifial parts, to localize the flames. > >LOL- localize the flames.... >I wonder with your hefty relay drive, how the switcher responds to a sudden discontinuation of current loading. Will the series inductor overvoltage for a while conducting through the TVS? I think so. That would be worth running through a sim.Done that sim, at least enough to demonstrate that the energy in the inductor could pull the +12 up pretty good. I don't have an LT Spice model for the LM2567, which is why I did the little breadboard. Yes, one reason to have the TVS is to clamp overshoots in the case of sudden unloading of the 12 volt buss. But in this particular case, a bit of overshoot won't do any harm. The +12 is driving relays and 2nd-level switchers that can stand 32 volts in. So the TVS basically protects against a hard switcher failure. When we have bipolar supplies, we add a big schottky to ground so a supply can't be pulled through to its opposite polarity, which can cause all sorts of problems. It looks like this entire system can be all-positive power supplies. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 28, 20192019-09-28
On Saturday, September 28, 2019 at 4:40:18 PM UTC-4, Steve Wilson wrote:> On Saturday, September 28, 2019 at 1:57:03 PM UTC-4, Winfield Hill wrote: > > jlarkin@highlandsniptechnology.com wrote... > > > > On 28 Sep 2019, Winfield Hill wrote: > > > >>> ... The TVS would just limit damage downstream ... > > > >> Exactly, my worry is the TVS, with its very high dissipation, > > >> could fail. Maybe it would fail shorted, but maybe not. An > > >> SCR running at 1V is safer. If you really want to be safe, > > >> use the serious fail-safe circuit Paul devised: > > > >>https://www.dropbox.com/s/a33pelolwzrdv37/9x.7_crowbar.pdf?dl=1 > > > > Way too complex to protect against a low-probability event. > > > It was protecting $8k of electronic PCBs. I thought > > the impact in your case would be pretty dramatic as > > well. A portion of the circuit might be sufficient. > > > Thanks, > > - WinThe previous version allowed the input to exceed the 36V maximum of the TL431. Here's the fix. Watch the wrap. Version 4 SHEET 1 1608 1700 WIRE 144 -208 -80 -208 WIRE 384 -208 144 -208 WIRE 688 -208 384 -208 WIRE 944 -208 688 -208 WIRE 144 -160 144 -208 WIRE 384 -160 384 -208 WIRE 944 -160 944 -208 WIRE 688 -144 688 -208 WIRE 832 -144 784 -144 WIRE 880 -144 832 -144 WIRE 896 -144 880 -144 WIRE 832 -80 832 -144 WIRE -80 -48 -80 -208 WIRE -32 -48 -80 -48 WIRE 16 -48 -32 -48 WIRE 144 -48 144 -80 WIRE 240 -48 144 -48 WIRE 384 -48 384 -80 WIRE 448 -48 384 -48 WIRE 528 -48 448 -48 WIRE 672 -48 608 -48 WIRE 736 -48 736 -80 WIRE 736 -48 672 -48 WIRE -80 -32 -80 -48 WIRE 16 -32 16 -48 WIRE 144 -32 144 -48 WIRE 944 -32 944 -64 WIRE 1024 -32 944 -32 WIRE 1040 -32 1024 -32 WIRE 240 0 240 -48 WIRE 304 0 240 0 WIRE 320 0 304 0 WIRE 944 0 944 -32 WIRE 832 16 832 0 WIRE -80 64 -80 48 WIRE 144 64 144 48 WIRE 384 80 384 48 WIRE 384 96 384 80 WIRE 944 96 944 80 WIRE 16 112 16 48 WIRE 48 112 16 112 WIRE 336 112 48 112 WIRE 16 144 16 112 WIRE 336 160 320 160 WIRE 320 176 320 160 WIRE 384 192 384 176 WIRE 16 240 16 224 FLAG -80 64 0 FLAG 384 192 0 FLAG -32 -48 Vin FLAG 16 240 0 FLAG 672 -48 Q1B FLAG 832 16 0 FLAG 944 96 0 FLAG 880 -144 M1G FLAG 1024 -32 Vout FLAG 320 176 0 FLAG 48 112 R1R3 FLAG 448 -48 R2R4 FLAG 144 64 0 FLAG 304 0 Q2B FLAG 384 80 Q2E SYMBOL voltage -80 -48 R0 WINDOW 39 0 0 Left 2 WINDOW 3 3 -182 Left 2 SYMATTR Value PULSE(0 50 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 368 -176 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 0 -48 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 0 128 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 784 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 89 64 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N5401 SYMBOL res 624 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 896 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 816 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 928 -16 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 384 192 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 SYMBOL npn 320 -48 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 128 -176 R0 SYMATTR InstName R7 SYMATTR Value 10K SYMBOL res 128 -48 R0 SYMATTR InstName R8 SYMATTR Value 10k TEXT 128 -288 Left 2 !.tran 0 1m 0 1u TEXT 128 -320 Left 2 ;'Overvoltage Protection TEXT 72 368 Left 2 !.model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=100 Bf=132.1 Ne=1.375 \n+Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 Nc=2 Isc=0 Ikr=0 Rc=1.6 Cjc=17.63p \n+Mjc=.5312 Vjc=.75 Fc=.5 Cje=73.39p Mje=.3777 Vje=.75 Tr=1.476n Tf=641.9p \n+Itf=0 Vtf=0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild) TEXT 72 504 Left 2 !.model Si7489DP VDMOS(Rg=3 Rd=31.2m Rs=1m Vto=-2.4 mtriode=2.2 Kp=35 \n+lambda=0.1 Cgdmax=6n Cgdmin=10p A=1 Cgs=4n cjo=200p M=.3 VJ=.9 Is=3.6p \n+Rb=5.5m mfg=Siliconix ksubthres=.1 Vds=-100 Ron=34m Qg=106n pchan) TEXT 72 328 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0) TEXT 456 136 Left 2 ;Replace the switch with a TL431
Reply by ●September 28, 20192019-09-28
On Saturday, September 28, 2019 at 6:19:36 PM UTC-4, jla...@highlandsniptechnology.com wrote:> On Sat, 28 Sep 2019 14:53:01 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Friday, September 27, 2019 at 5:29:33 PM UTC-4, John Larkin wrote: > >> On Fri, 27 Sep 2019 13:47:45 -0700 (PDT), > >> bloggs.fredbloggs.fred@gmail.com wrote: > >> > >> >On Thursday, September 26, 2019 at 5:56:15 PM UTC-4, John Larkin wrote: > >> >> I have a 48 volt power supply and I want to drive a lot of relays and > >> >> uPs and FPGAs and stuff, so I figured I'd knock it down to 12 volts > >> >> first. > >> >> > >> >> We have LM2567HV-ADJ in stock, a 52 KHz Simple Switcher probably > >> >> designed by druids during the last ice age. Figured I'd breadboard the > >> >> reg just for fun. A boy gets tired of typing all day. > >> >> > >> >> https://www.dropbox.com/sh/ajtqs7c1nswfhey/AABi7r0gchljjrxka4aHZItfa?dl=0 > >> >> > >> >> > >> >> Works pretty well, actually. Nothing gets very warm at 1 amp out. > >> >> > >> >> Yes, that unshielded drum core will spray field everywhere, but then I > >> >> am simulating alternators. > >> > > >> >Isn't that 12V TVS cutting things close? > >> > >> A 12 volt TVS doesn't conduct at 12 volts. More like 14. > >> > >> If the reg fails, it would push 48 volts into 7 PC boards that are all > >> expecting 12. I could include the TVS and maybe an 0805 series > >> resistor as sacrifial parts, to localize the flames. > > > >LOL- localize the flames.... > >I wonder with your hefty relay drive, how the switcher responds to a sudden discontinuation of current loading. Will the series inductor overvoltage for a while conducting through the TVS? I think so. That would be worth running through a sim. > > > Done that sim, at least enough to demonstrate that the energy in the > inductor could pull the +12 up pretty good. I don't have an LT Spice > model for the LM2567, which is why I did the little breadboard. > > Yes, one reason to have the TVS is to clamp overshoots in the case of > sudden unloading of the 12 volt buss. But in this particular case, a > bit of overshoot won't do any harm. The +12 is driving relays and > 2nd-level switchers that can stand 32 volts in. So the TVS basically > protects against a hard switcher failure.Also eliminates any possibility of avalanche breakdown of the coil driver turning off, although almost any output capacitance should buy enough time to prevent that too. There shouldn't be secondary breakdown for a driver turning on.> > When we have bipolar supplies, we add a big schottky to ground so a > supply can't be pulled through to its opposite polarity, which can > cause all sorts of problems. > > It looks like this entire system can be all-positive power supplies. > > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
