On 2022/10/06 7:50 a.m., John Larkin wrote:> On Wed, 5 Oct 2022 23:24:26 -0700, John Robertson <jrr@flippers.com> > wrote: > >> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) >> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K >> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL >> controller. > > That's not clear. Got a schematic?Yes: https://www.flippers.com/images/delet/74LS138_Lamp_Driver.png Think going to a 7445 sub-board will be best way around this. It was the designer who made an error on using the 138 and I am simply trying to rescue 5 populated boards...blame the Scottish side of my family! John :-#)#> > > >> >> Problem is of course, that R2 puts the ~20VDC to the TTL output gate on >> a 74LS138. >> >> Trying to solve this without a driver transistor. The circuit is for a >> 1ms ~20V strobe pulse repeated every ten ms. >> >> I thought of putting a 10ufd cap in series with R2, but don't like >> electrolytics as they fail after a few thousand hours. >> >> Possible to use a 15V or so Zener Diode, but the Vbb is not regulated so >> that won't work reliably. >> >> Anyone have a single component in mind that will essentially emulate >> (isolate) an Open-Collector output for the 138? >> >> Thanks! >> >> John :-#)#-- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."
Emulating Open-Collector operation with TTL 74LS138...
Started by ●October 6, 2022
Reply by ●October 6, 20222022-10-06
Reply by ●October 6, 20222022-10-06
John Robertson wrote:> On 2022/10/06 4:41 a.m., Phil Hobbs wrote: >> John Robertson wrote: >>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) >>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K >>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL >>> controller. >>> >>> Problem is of course, that R2 puts the ~20VDC to the TTL output gate >>> on a 74LS138. >>> >>> Trying to solve this without a driver transistor. The circuit is for >>> a 1ms ~20V strobe pulse repeated every ten ms. >>> >>> I thought of putting a 10ufd cap in series with R2, but don't like >>> electrolytics as they fail after a few thousand hours. >>> >>> Possible to use a 15V or so Zener Diode, but the Vbb is not regulated >>> so that won't work reliably. >>> >>> Anyone have a single component in mind that will essentially emulate >>> (isolate) an Open-Collector output for the 138? >>> >>> Thanks! >>> >>> John :-#)# >>> >> Switch it to a 139 and use a 2N7002? >> >> Cheers >> >> Phil Hobbs >> > > Well, this is to fix 5 x PCBs we are stuck with at the moment, next run > will fix the drives - either 7445s or 138 with P-Channel MOSFETs and > drivers. > > Circuit I am trying to fix with fewest components - one x two legged > device preferred per 138 output: > > https://www.flippers.com/images/delete/74LS138_Lamp_Driver.png > > VLAMP is roughly 20VDC. > > Thanks, > > John :-#)#The MOSFET cascode thing is pretty good actually, if you put a diode to the supply or want to live dangerously and rely on the ESD protection to discharge the gate. If it's a matter of using the boards or tossing them, there's not much to lose by using barefoot FETs. 2N7000s are still around IIRC, and they're TO-92. There are multiple-section devices such as the Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●October 6, 20222022-10-06
torsdag den 6. oktober 2022 kl. 18.51.13 UTC+2 skrev Phil Hobbs:> John Robertson wrote: > > On 2022/10/06 4:41 a.m., Phil Hobbs wrote: > >> John Robertson wrote: > >>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) > >>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K > >>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL > >>> controller. > >>> > >>> Problem is of course, that R2 puts the ~20VDC to the TTL output gate > >>> on a 74LS138. > >>> > >>> Trying to solve this without a driver transistor. The circuit is for > >>> a 1ms ~20V strobe pulse repeated every ten ms. > >>> > >>> I thought of putting a 10ufd cap in series with R2, but don't like > >>> electrolytics as they fail after a few thousand hours. > >>> > >>> Possible to use a 15V or so Zener Diode, but the Vbb is not regulated > >>> so that won't work reliably. > >>> > >>> Anyone have a single component in mind that will essentially emulate > >>> (isolate) an Open-Collector output for the 138? > >>> > >>> Thanks! > >>> > >>> John :-#)# > >>> > >> Switch it to a 139 and use a 2N7002? > >> > >> Cheers > >> > >> Phil Hobbs > >> > > > > Well, this is to fix 5 x PCBs we are stuck with at the moment, next run > > will fix the drives - either 7445s or 138 with P-Channel MOSFETs and > > drivers. > > > > Circuit I am trying to fix with fewest components - one x two legged > > device preferred per 138 output: > > > > https://www.flippers.com/images/delete/74LS138_Lamp_Driver.png > > > > VLAMP is roughly 20VDC. > > > > Thanks, > > > > John :-#)# > The MOSFET cascode thing is pretty good actually, if you put a diode to > the supply or want to live dangerously and rely on the ESD protection to > discharge the gate. If it's a matter of using the boards or tossing > them, there's not much to lose by using barefoot FETs. >'138 is push-pull, though very wimpy high side
Reply by ●October 6, 20222022-10-06
On Thursday, October 6, 2022 at 12:44:21 PM UTC-4, John Robertson wrote:> On 2022/10/06 7:50 a.m., John Larkin wrote: > > On Wed, 5 Oct 2022 23:24:26 -0700, John Robertson <j...@flippers.com> > > wrote: > > > >> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) > >> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K > >> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL > >> controller. > > > > That's not clear. Got a schematic? > Yes: > > https://www.flippers.com/images/delet/74LS138_Lamp_Driver.png > > Think going to a 7445 sub-board will be best way around this. It was the > designer who made an error on using the 138 and I am simply trying to > rescue 5 populated boards...blame the Scottish side of my family!I still think you can make the capacitor idea work. It would need a cap and a pullup resistor for each output. Or you could use a Schottky diode to +5V instead of the resistor. That would make the recovery time shorter after a pulse and protect the 138 output. -- Rick C. ++ Get 1,000 miles of free Supercharging ++ Tesla referral code - https://ts.la/richard11209
Reply by ●October 6, 20222022-10-06
Lasse Langwadt Christensen wrote:> torsdag den 6. oktober 2022 kl. 18.51.13 UTC+2 skrev Phil Hobbs: >> John Robertson wrote: >>> On 2022/10/06 4:41 a.m., Phil Hobbs wrote: >>>> John Robertson wrote: >>>>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) >>>>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K >>>>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL >>>>> controller. >>>>> >>>>> Problem is of course, that R2 puts the ~20VDC to the TTL output gate >>>>> on a 74LS138. >>>>> >>>>> Trying to solve this without a driver transistor. The circuit is for >>>>> a 1ms ~20V strobe pulse repeated every ten ms. >>>>> >>>>> I thought of putting a 10ufd cap in series with R2, but don't like >>>>> electrolytics as they fail after a few thousand hours. >>>>> >>>>> Possible to use a 15V or so Zener Diode, but the Vbb is not regulated >>>>> so that won't work reliably. >>>>> >>>>> Anyone have a single component in mind that will essentially emulate >>>>> (isolate) an Open-Collector output for the 138? >>>>> >>>>> Thanks! >>>>> >>>>> John :-#)# >>>>> >>>> Switch it to a 139 and use a 2N7002? >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>> >>> Well, this is to fix 5 x PCBs we are stuck with at the moment, next run >>> will fix the drives - either 7445s or 138 with P-Channel MOSFETs and >>> drivers. >>> >>> Circuit I am trying to fix with fewest components - one x two legged >>> device preferred per 138 output: >>> >>> https://www.flippers.com/images/delete/74LS138_Lamp_Driver.png >>> >>> VLAMP is roughly 20VDC. >>> >>> Thanks, >>> >>> John :-#)# >> The MOSFET cascode thing is pretty good actually, if you put a diode to >> the supply or want to live dangerously and rely on the ESD protection to >> discharge the gate. If it's a matter of using the boards or tossing >> them, there's not much to lose by using barefoot FETs. >> > > '138 is push-pull, though very wimpy high side >Sure, but anything above +4ish reverse-biases the upper output transistor. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●October 6, 20222022-10-06
torsdag den 6. oktober 2022 kl. 20.04.09 UTC+2 skrev Phil Hobbs:> Lasse Langwadt Christensen wrote: > > torsdag den 6. oktober 2022 kl. 18.51.13 UTC+2 skrev Phil Hobbs: > >> John Robertson wrote: > >>> On 2022/10/06 4:41 a.m., Phil Hobbs wrote: > >>>> John Robertson wrote: > >>>>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) > >>>>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K > >>>>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL > >>>>> controller. > >>>>> > >>>>> Problem is of course, that R2 puts the ~20VDC to the TTL output gate > >>>>> on a 74LS138. > >>>>> > >>>>> Trying to solve this without a driver transistor. The circuit is for > >>>>> a 1ms ~20V strobe pulse repeated every ten ms. > >>>>> > >>>>> I thought of putting a 10ufd cap in series with R2, but don't like > >>>>> electrolytics as they fail after a few thousand hours. > >>>>> > >>>>> Possible to use a 15V or so Zener Diode, but the Vbb is not regulated > >>>>> so that won't work reliably. > >>>>> > >>>>> Anyone have a single component in mind that will essentially emulate > >>>>> (isolate) an Open-Collector output for the 138? > >>>>> > >>>>> Thanks! > >>>>> > >>>>> John :-#)# > >>>>> > >>>> Switch it to a 139 and use a 2N7002? > >>>> > >>>> Cheers > >>>> > >>>> Phil Hobbs > >>>> > >>> > >>> Well, this is to fix 5 x PCBs we are stuck with at the moment, next run > >>> will fix the drives - either 7445s or 138 with P-Channel MOSFETs and > >>> drivers. > >>> > >>> Circuit I am trying to fix with fewest components - one x two legged > >>> device preferred per 138 output: > >>> > >>> https://www.flippers.com/images/delete/74LS138_Lamp_Driver.png > >>> > >>> VLAMP is roughly 20VDC. > >>> > >>> Thanks, > >>> > >>> John :-#)# > >> The MOSFET cascode thing is pretty good actually, if you put a diode to > >> the supply or want to live dangerously and rely on the ESD protection to > >> discharge the gate. If it's a matter of using the boards or tossing > >> them, there's not much to lose by using barefoot FETs. > >> > > > > '138 is push-pull, though very wimpy high side > > > Sure, but anything above +4ish reverse-biases the upper output transistor. > Cheerswith the upper transistor on does it ever get there?
Reply by ●October 6, 20222022-10-06
Lasse Langwadt Christensen wrote:> torsdag den 6. oktober 2022 kl. 20.04.09 UTC+2 skrev Phil Hobbs: >> Lasse Langwadt Christensen wrote: >>> torsdag den 6. oktober 2022 kl. 18.51.13 UTC+2 skrev Phil Hobbs: >>>> John Robertson wrote: >>>>> On 2022/10/06 4:41 a.m., Phil Hobbs wrote: >>>>>> John Robertson wrote: >>>>>>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) >>>>>>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K >>>>>>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL >>>>>>> controller. >>>>>>> >>>>>>> Problem is of course, that R2 puts the ~20VDC to the TTL output gate >>>>>>> on a 74LS138. >>>>>>> >>>>>>> Trying to solve this without a driver transistor. The circuit is for >>>>>>> a 1ms ~20V strobe pulse repeated every ten ms. >>>>>>> >>>>>>> I thought of putting a 10ufd cap in series with R2, but don't like >>>>>>> electrolytics as they fail after a few thousand hours. >>>>>>> >>>>>>> Possible to use a 15V or so Zener Diode, but the Vbb is not regulated >>>>>>> so that won't work reliably. >>>>>>> >>>>>>> Anyone have a single component in mind that will essentially emulate >>>>>>> (isolate) an Open-Collector output for the 138? >>>>>>> >>>>>>> Thanks! >>>>>>> >>>>>>> John :-#)# >>>>>>> >>>>>> Switch it to a 139 and use a 2N7002? >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>>> >>>>> >>>>> Well, this is to fix 5 x PCBs we are stuck with at the moment, next run >>>>> will fix the drives - either 7445s or 138 with P-Channel MOSFETs and >>>>> drivers. >>>>> >>>>> Circuit I am trying to fix with fewest components - one x two legged >>>>> device preferred per 138 output: >>>>> >>>>> https://www.flippers.com/images/delete/74LS138_Lamp_Driver.png >>>>> >>>>> VLAMP is roughly 20VDC. >>>>> >>>>> Thanks, >>>>> >>>>> John :-#)# >>>> The MOSFET cascode thing is pretty good actually, if you put a diode to >>>> the supply or want to live dangerously and rely on the ESD protection to >>>> discharge the gate. If it's a matter of using the boards or tossing >>>> them, there's not much to lose by using barefoot FETs. >>>> >>> >>> '138 is push-pull, though very wimpy high side >>> >> Sure, but anything above +4ish reverse-biases the upper output transistor. >> Cheers > > with the upper transistor on does it ever get there? > >Sure, it's an NPN emitter. If it were a NFET, it would be fine. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●October 6, 20222022-10-06
On Thu, 6 Oct 2022 09:44:13 -0700, John Robertson <jrr@flippers.com> wrote:>On 2022/10/06 7:50 a.m., John Larkin wrote: >> On Wed, 5 Oct 2022 23:24:26 -0700, John Robertson <jrr@flippers.com> >> wrote: >> >>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) >>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K >>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL >>> controller. >> >> That's not clear. Got a schematic? > >Yes: > >https://www.flippers.com/images/delet/74LS138_Lamp_Driver.png404 error.
Reply by ●October 6, 20222022-10-06
On 2022/10/06 12:41 p.m., John Larkin wrote:> On Thu, 6 Oct 2022 09:44:13 -0700, John Robertson <jrr@flippers.com> > wrote: > >> On 2022/10/06 7:50 a.m., John Larkin wrote: >>> On Wed, 5 Oct 2022 23:24:26 -0700, John Robertson <jrr@flippers.com> >>> wrote: >>> >>>> Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) >>>> emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K >>>> resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL >>>> controller. >>> >>> That's not clear. Got a schematic? >> >> Yes: >> >> https://www.flippers.com/images/delet/74LS138_Lamp_Driver.png > > > 404 error. >sorry: https://www.flippers.com/images/delete/74LS138_Lamp_Driver.png Currently wire wrapping up a board to jam a 7445 in place of the 138. John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."
Reply by ●October 6, 20222022-10-06
torsdag den 6. oktober 2022 kl. 18.35.18 UTC+2 skrev Ricky:> On Thursday, October 6, 2022 at 12:17:08 PM UTC-4, lang...@fonz.dk wrote: > > torsdag den 6. oktober 2022 kl. 17.51.16 UTC+2 skrev Fred Bloggs: > > > On Thursday, October 6, 2022 at 11:37:46 AM UTC-4, lang...@fonz.dk wrote: > > > > torsdag den 6. oktober 2022 kl. 17.29.21 UTC+2 skrev Fred Bloggs: > > > > > On Thursday, October 6, 2022 at 2:24:33 AM UTC-4, John Robertson wrote: > > > > > > Have a circuit that needs repair. Uses a TIP125 (NPN, Darlington) > > > > > > emitter tied to Vbb (~20VDC). Collector to load, then to ground. 1K > > > > > > resistor (R1) pullup on Base to Vbb, and a second 1KR (R2) to the TTL > > > > > > controller. > > > > > > > > > > > > Problem is of course, that R2 puts the ~20VDC to the TTL output gate on > > > > > > a 74LS138. > > > > > > > > > > > > Trying to solve this without a driver transistor. The circuit is for a > > > > > > 1ms ~20V strobe pulse repeated every ten ms. > > > > > > > > > > > > I thought of putting a 10ufd cap in series with R2, but don't like > > > > > > electrolytics as they fail after a few thousand hours. > > > > > > > > > > > > Possible to use a 15V or so Zener Diode, but the Vbb is not regulated so > > > > > > that won't work reliably. > > > > > > > > > > > > Anyone have a single component in mind that will essentially emulate > > > > > > (isolate) an Open-Collector output for the 138? > > > > > The TIP125 is a complementary dual. > > > > it is? https://www.onsemi.com/pdf/datasheet/tip120-d.pdf > > > Yeah it is. See Figure 1. All of that is in that TO-220 looking package. > > and the three missing legs are where? > > > > TIP120, TIP121, TIP122 (NPN); is the right drawing > > > > TIP125, TIP126, TIP127 (PNP); is the left drawing > It would seem a combination of a high side PNP driver and a low side NPN level shifter would be a useful, single package device. Is there a reason why this is hard to make on a single die? >what package would you put it in? you'd need more than 3 pins I think the closest is arrays like UDN2981
