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#1
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Indicator relay post-mortem.
Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). |
#2
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation |
#3
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). |
#4
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote: "John Larkin" wrote in message .. . On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation |
#5
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message . .. On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! |
#6
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote: "John Larkin" wrote in message .. . On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message ... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators |
#7
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message . .. On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message m... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG The bean-counters at the firm that made it would freak out if the engineers showed them that! |
#8
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Wed, 6 Jun 2012 16:37:47 +0100, "Ian Field"
wrote: "John Larkin" wrote in message .. . On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message ... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message om... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG The bean-counters at the firm that made it would freak out if the engineers showed them that! Yeah, it makes better financial sense to sell something that's a few cents cheaper, and let the buyers deal with the blown fet gates. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators |
#9
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote: On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message . .. On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message m... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG Correction, the main mosfet drain has to move a notch left, before the diode. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation |
#10
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Wed, 6 Jun 2012 16:37:47 +0100, "Ian Field" wrote: "John Larkin" wrote in message . .. On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message m... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:6c7qs797vd7f771hct3n65emcf93iqaktb@4ax. com... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG The bean-counters at the firm that made it would freak out if the engineers showed them that! Yeah, it makes better financial sense to sell something that's a few cents cheaper, and let the buyers deal with the blown fet gates. The relay was date stamped 98 - which is older than the bike I took it off. So it had already been salvaged from elsewhere and fitted to the bike as replacement for whatever went brfore it. As I stated in my original post, I wrongly blamed the relay for intermittent operation which turned out to be a corroded connector hidden under the tank (in my defence; it was much easier to swap the relay than take the tank off). At the end of the day: the astable they've used is cheaper and more reliable than a 555 and all the extra gubbins to keep it safe in the automotive environment. |
#11
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin wrote: On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message ... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message om... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG Correction, the main mosfet drain has to move a notch left, before the diode. Wondered how long it'd take you to notice that. |
#12
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field"
wrote: "John Larkin" wrote in message .. . On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin wrote: On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message m... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:6c7qs797vd7f771hct3n65emcf93iqaktb@4ax. com... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG Correction, the main mosfet drain has to move a notch left, before the diode. Wondered how long it'd take you to notice that. Well thanks for not pummeling me with insults in the interim. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation |
#13
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field" wrote: "John Larkin" wrote in message . .. On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin wrote: On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message om... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:6c7qs797vd7f771hct3n65emcf93iqaktb@4ax .com... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG Correction, the main mosfet drain has to move a notch left, before the diode. Wondered how long it'd take you to notice that. Well thanks for not pummeling me with insults in the interim. That's JF's & JT's job - and most of us have to endure their schoolyard bully act! |
#14
Posted to alt.binaries.schematics.electronic
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Indicator relay post-mortem.
On Wed, 6 Jun 2012 22:46:37 +0100, "Ian Field"
wrote: "John Larkin" wrote in message .. . On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field" wrote: "John Larkin" wrote in message ... On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin wrote: On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:ehlss71ic567t7f63tfsrggp0upabbdfr9@4ax. com... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:6c7qs797vd7f771hct3n65emcf93iqaktb@4a x.com... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG Correction, the main mosfet drain has to move a notch left, before the diode. Wondered how long it'd take you to notice that. Well thanks for not pummeling me with insults in the interim. That's JF's & JT's job - and most of us have to endure their schoolyard bully act! So, we finally have a thread where it's possible, actually possible, that a 555 might be useful, and JF is MIA. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation |
#15
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Indicator relay post-mortem.
"John Larkin" wrote in message ... On Wed, 6 Jun 2012 22:46:37 +0100, "Ian Field" wrote: "John Larkin" wrote in message . .. On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field" wrote: "John Larkin" wrote in message m... On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin wrote: On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:ehlss71ic567t7f63tfsrggp0upabbdfr9@4ax .com... On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field" wrote: "John Larkin" wrote in message news:6c7qs797vd7f771hct3n65emcf93iqaktb@4 ax.com... On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field" wrote: Its a 2-terminal relay for a motorcycle, after adding an earth lead so I could fit a car type; I then discovered that the intermittent operation was due to a corroded connector block hidden under the tank. After breaking up the epoxy potting I found the old relay was blameless. The circuit could probably be adapted for 6V with a logic level MOSFET - but would need 2 in parallel to handle twice the current (don't forget filament cold resistance surge!). Now *that* is an application for a 555! Whoever designed that may have had reservations about putting a 555 into the automotive envirenment - a quick google shows the bipolar 555 as having a 16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the 60V MOSFET is spec'ed for the automotive environment according to the datasheet. Note however the 1kV rating of the 1N4007 they've used to isolate the reservoir from the MOSFET is somewhat superfluous, it only has to withstand the reservoir voltage as any externally applied reverse voltage would be clamped by the MOSFET body diode (maybe they got a better price break on quantity 4007s). The fet gate is only rated for 20 volts, and the diode/cap will peak detect and store any load dump spikes. So some sort of transzorb thing (with a depletion mosfet?!) might be prudent. I'm curious to see a schematic of a depletion MOSFET in that application? At first blush I'm thinking maybe an oscillator driving a negative O/P diode pump to generate the pinch off bias. Wouldn't do much for production costs though! No, I meant that you could use a depletion fet in the load-dump protection part, something like this: https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG Correction, the main mosfet drain has to move a notch left, before the diode. Wondered how long it'd take you to notice that. Well thanks for not pummeling me with insults in the interim. That's JF's & JT's job - and most of us have to endure their schoolyard bully act! So, we finally have a thread where it's possible, actually possible, that a 555 might be useful, and JF is MIA. I'm still not convinced a 555 is the best way to go - I'd put a stopper resistor from the 555 O/P to the gate, then I could add a 16V zener from gate to cathode of the isolating diode. that should nip any cummulative spikes that try to push the reservoir voltage above the limit of Vcc. In the failsafe condition; the indicators would be on longer than they should, but the 555 should be safe enough. |
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