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Overvoltage and reverse voltage protection
Dear all
I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Richard |
On Sun, 11 Jan 2004 19:44:19 +0800, Richard Hosking
wrote: Dear all I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Richard Rick, one way for reverse protection is to include a bridge recifier in the rigs power line ( internally fitted ), but this causes a drop in available volts. I prefer a diode into a relay coil, with the relay contacts enabling the power when the relay coil is correctly polarised and powered ( also internally fitted ). This enables full volts to the rig and also gives reverse protection, however this is at the cost of further ( and some may say excessive ) drain of the power source. Over voltage should be by fuse and a crowbar circuit. Do a search on crowbar for details. The diode + relay circuit should be obvious to you, I use a 9v relay coil with a 1N4001 in the activation side and a DPDT contact,in parallel, to switch the power. For the power you are talking about a 14pin DIL relay should be adequate. HTH, Mike W, G8NXD qthr |
On Sun, 11 Jan 2004 19:44:19 +0800, Richard Hosking
wrote: Dear all I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Richard Rick, one way for reverse protection is to include a bridge recifier in the rigs power line ( internally fitted ), but this causes a drop in available volts. I prefer a diode into a relay coil, with the relay contacts enabling the power when the relay coil is correctly polarised and powered ( also internally fitted ). This enables full volts to the rig and also gives reverse protection, however this is at the cost of further ( and some may say excessive ) drain of the power source. Over voltage should be by fuse and a crowbar circuit. Do a search on crowbar for details. The diode + relay circuit should be obvious to you, I use a 9v relay coil with a 1N4001 in the activation side and a DPDT contact,in parallel, to switch the power. For the power you are talking about a 14pin DIL relay should be adequate. HTH, Mike W, G8NXD qthr |
Mike W wrote:
Over voltage should be by fuse and a crowbar circuit. Do a search on crowbar for details. If you already have a fuse & crowbar circuit for overvoltage, wouldn't the easy way to handle reverse polarity be a diode hooked in the (normally) non-conducting direction across the output? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
Mike W wrote:
Over voltage should be by fuse and a crowbar circuit. Do a search on crowbar for details. If you already have a fuse & crowbar circuit for overvoltage, wouldn't the easy way to handle reverse polarity be a diode hooked in the (normally) non-conducting direction across the output? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
I'm not understanding something here. You want to design a power supply that protects against reverse voltage and overvoltage. OK. Is this power supply a battery or are you actually building a power supply that runs from the wall outlet? The requirements are quite different, depending on what you are trying to achieve. Jim Richard Hosking shared these priceless pearls of wisdom: -Dear all -I want to design a power supply for a low power rig with protection for -reverse and overvoltage. Jim Weir, VP Eng. RST Eng. WX6RST A&P, CFI, and other good alphabet soup |
I'm not understanding something here. You want to design a power supply that protects against reverse voltage and overvoltage. OK. Is this power supply a battery or are you actually building a power supply that runs from the wall outlet? The requirements are quite different, depending on what you are trying to achieve. Jim Richard Hosking shared these priceless pearls of wisdom: -Dear all -I want to design a power supply for a low power rig with protection for -reverse and overvoltage. Jim Weir, VP Eng. RST Eng. WX6RST A&P, CFI, and other good alphabet soup |
In article ,
says... Dear all I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Power Schottky diodes are available that have a forward voltage drop of 0.3 or less. More expensive, yes, but they really do work. -- Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute (Known to some as Bruce Lane, KC7GR) kyrrin a/t bluefeathertech d-o=t c&o&m Motorola Radio Programming & Service Available - http://www.bluefeathertech.com/rf.html "Quando Omni Flunkus Moritati" (Red Green) |
On Sun, 11 Jan 2004 14:05:21 GMT, (Mike W)
wrote: The diode + relay circuit should be obvious to you, I use a 9v relay coil with a 1N4001 in the activation side and a DPDT contact,in parallel, to switch the power. For the power you are talking about a 14pin DIL relay should be adequate. HTH, Mike W, G8NXD qthr I'd like to call it "the PYE method" since it is generally applied in those Westminster, Vanguard and Cambridge sets, while other manufacturers only use a diode. I've copied it for the larger sets which are often used in different places. The application of relay has the advantage that nothing happens if you use the wrong polarity - unless you have shortcircuit between two chassises, then you should apply a two-pole relay. Make sure that the relay stays operated under different operation, check that the relay operates with 9V. Remember to put a diode or other spark suppression across the coil, too. 73 LA8AK, http://home.online.no/~la8ak/c.htm -- Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails Cannot check every email manually. Please use intelligent title for email. Mails without titles or using just "hi" is deleted |
On Sun, 11 Jan 2004 14:05:21 GMT, (Mike W)
wrote: The diode + relay circuit should be obvious to you, I use a 9v relay coil with a 1N4001 in the activation side and a DPDT contact,in parallel, to switch the power. For the power you are talking about a 14pin DIL relay should be adequate. HTH, Mike W, G8NXD qthr I'd like to call it "the PYE method" since it is generally applied in those Westminster, Vanguard and Cambridge sets, while other manufacturers only use a diode. I've copied it for the larger sets which are often used in different places. The application of relay has the advantage that nothing happens if you use the wrong polarity - unless you have shortcircuit between two chassises, then you should apply a two-pole relay. Make sure that the relay stays operated under different operation, check that the relay operates with 9V. Remember to put a diode or other spark suppression across the coil, too. 73 LA8AK, http://home.online.no/~la8ak/c.htm -- Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails Cannot check every email manually. Please use intelligent title for email. Mails without titles or using just "hi" is deleted |
In article ,
Dr. A.T. Squeegee wrote: I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Power Schottky diodes are available that have a forward voltage drop of 0.3 or less. More expensive, yes, but they really do work. Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. When a power supply of the correct polarity is hooked up, the MOSFET's intrinsic substrate diode is biased forward (conducting normally) and the MOSFET is turned on "hard" (giving a low Rds, and thus a very low forward voltage drop). If the supply is hooked up backwards, the MOSFET is turned off (the gate is pulled down towards hard depletion) and the substrate diode is reverse-biased, switching it off. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
In article ,
Dr. A.T. Squeegee wrote: I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Power Schottky diodes are available that have a forward voltage drop of 0.3 or less. More expensive, yes, but they really do work. Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. When a power supply of the correct polarity is hooked up, the MOSFET's intrinsic substrate diode is biased forward (conducting normally) and the MOSFET is turned on "hard" (giving a low Rds, and thus a very low forward voltage drop). If the supply is hooked up backwards, the MOSFET is turned off (the gate is pulled down towards hard depletion) and the substrate diode is reverse-biased, switching it off. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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In article ,
Mike W wrote: Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. Nice one Dave Not my idea originally, by any means. If I recall correctly I first saw it in Bob Pease's "Troubleshooting Analog Circuits" book - a text I recommend to anyone who is fiddling around with analog circuitry in any way. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
In article ,
Mike W wrote: Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. Nice one Dave Not my idea originally, by any means. If I recall correctly I first saw it in Bob Pease's "Troubleshooting Analog Circuits" book - a text I recommend to anyone who is fiddling around with analog circuitry in any way. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Jim
The rig will be powered from a 12V source eg battery/AC wallwart /whatever. However, internally the rig needs various voltages, including 1.8V for logic and -12V. I want to ptotect against inadvertent overvoltage or reverse voltage. I want it to be as efficient as possible, so I dont want to use a linear regulator. SMPS seems the obvious choice. I may well shield the PSU section, and isolate the ground etc to reduce noise. I was seeking advice from the experts here as to whether the idea is feasible and whether there is a redaymade solution. Richard Jim Weir wrote: I'm not understanding something here. You want to design a power supply that protects against reverse voltage and overvoltage. OK. Is this power supply a battery or are you actually building a power supply that runs from the wall outlet? The requirements are quite different, depending on what you are trying to achieve. Jim Richard Hosking shared these priceless pearls of wisdom: -Dear all -I want to design a power supply for a low power rig with protection for -reverse and overvoltage. Jim Weir, VP Eng. RST Eng. WX6RST A&P, CFI, and other good alphabet soup |
Jim
The rig will be powered from a 12V source eg battery/AC wallwart /whatever. However, internally the rig needs various voltages, including 1.8V for logic and -12V. I want to ptotect against inadvertent overvoltage or reverse voltage. I want it to be as efficient as possible, so I dont want to use a linear regulator. SMPS seems the obvious choice. I may well shield the PSU section, and isolate the ground etc to reduce noise. I was seeking advice from the experts here as to whether the idea is feasible and whether there is a redaymade solution. Richard Jim Weir wrote: I'm not understanding something here. You want to design a power supply that protects against reverse voltage and overvoltage. OK. Is this power supply a battery or are you actually building a power supply that runs from the wall outlet? The requirements are quite different, depending on what you are trying to achieve. Jim Richard Hosking shared these priceless pearls of wisdom: -Dear all -I want to design a power supply for a low power rig with protection for -reverse and overvoltage. Jim Weir, VP Eng. RST Eng. WX6RST A&P, CFI, and other good alphabet soup |
This sounds like a good solution
Thanks Richard Dave Platt wrote: In article , Dr. A.T. Squeegee wrote: I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Power Schottky diodes are available that have a forward voltage drop of 0.3 or less. More expensive, yes, but they really do work. Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. When a power supply of the correct polarity is hooked up, the MOSFET's intrinsic substrate diode is biased forward (conducting normally) and the MOSFET is turned on "hard" (giving a low Rds, and thus a very low forward voltage drop). If the supply is hooked up backwards, the MOSFET is turned off (the gate is pulled down towards hard depletion) and the substrate diode is reverse-biased, switching it off. |
This sounds like a good solution
Thanks Richard Dave Platt wrote: In article , Dr. A.T. Squeegee wrote: I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Power Schottky diodes are available that have a forward voltage drop of 0.3 or less. More expensive, yes, but they really do work. Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. When a power supply of the correct polarity is hooked up, the MOSFET's intrinsic substrate diode is biased forward (conducting normally) and the MOSFET is turned on "hard" (giving a low Rds, and thus a very low forward voltage drop). If the supply is hooked up backwards, the MOSFET is turned off (the gate is pulled down towards hard depletion) and the substrate diode is reverse-biased, switching it off. |
On Sun, 11 Jan 2004 21:23:21 GMT, (Mike W)
wrote: On Sun, 11 Jan 2004 21:17:43 -0000, (Dave Platt) wrote: Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. Nice one Dave indeed, if you could tell me about a MOSFET without protexion diode -- Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails Cannot check every email manually. Please use intelligent title for email. Mails without titles or using just "hi" is deleted |
On Sun, 11 Jan 2004 21:23:21 GMT, (Mike W)
wrote: On Sun, 11 Jan 2004 21:17:43 -0000, (Dave Platt) wrote: Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. Nice one Dave indeed, if you could tell me about a MOSFET without protexion diode -- Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails Cannot check every email manually. Please use intelligent title for email. Mails without titles or using just "hi" is deleted |
In article ,
J M Noeding wrote: Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. Nice one Dave indeed, if you could tell me about a MOSFET without protexion diode That's why I mentioned hooking it up with the source and drain leads in the reverse of the usual orientation. In the normal hookup situation, the intrinsic/substrate/protection diode would prevent the circuit from working as one would want (as you clearly understand). However, by hooking up the MOSFET "backwards" (e.g. an NMOSFET with the drain on the negative side), the orientation of the intrinsic diode is reversed. It'll be forward-biased when the power supply is hooked up the way you want it, and would be conductive. It probably won't have a chance to conduct, though, since you'll be biasing the gate up several volts above either the source or drain pins, turning on the MOSFET, and the relatively low Rds[on] of the MOSFET will keep the voltage drop across the MOSFET down below the substrate diode's voltage drop. If the supply connections are reversed, the MOSFET itself will be biased off, and the intrinsic protection diode will be reverse-biased and will not conduct. It's an odd trick. Many (most?) JFETs have a highly symmetrical internal construction - the distinction between source and drain is a matter of convention rather than construction. A typical MOSFET's construction is not entirely symmetrical... but, according to the description I've read of this trick in Pease's book, it _is_ symmetrical enough to allow it to be used with source and drain reversed, in this particular application. By flipping 'em around, you make the intrinsic diode work for you rather than against you. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
In article ,
J M Noeding wrote: Another trick I've seen is to use a hefty power MOSFET (one with a low Rds[on]), with the source and drain leads reversed, in series with the power. Depending on the voltages involved, you can either connect the gate directly to the opposite side of the power supply, or (if the supply voltage may exceed the Vgs limit) to a high-Z resistive divider. Nice one Dave indeed, if you could tell me about a MOSFET without protexion diode That's why I mentioned hooking it up with the source and drain leads in the reverse of the usual orientation. In the normal hookup situation, the intrinsic/substrate/protection diode would prevent the circuit from working as one would want (as you clearly understand). However, by hooking up the MOSFET "backwards" (e.g. an NMOSFET with the drain on the negative side), the orientation of the intrinsic diode is reversed. It'll be forward-biased when the power supply is hooked up the way you want it, and would be conductive. It probably won't have a chance to conduct, though, since you'll be biasing the gate up several volts above either the source or drain pins, turning on the MOSFET, and the relatively low Rds[on] of the MOSFET will keep the voltage drop across the MOSFET down below the substrate diode's voltage drop. If the supply connections are reversed, the MOSFET itself will be biased off, and the intrinsic protection diode will be reverse-biased and will not conduct. It's an odd trick. Many (most?) JFETs have a highly symmetrical internal construction - the distinction between source and drain is a matter of convention rather than construction. A typical MOSFET's construction is not entirely symmetrical... but, according to the description I've read of this trick in Pease's book, it _is_ symmetrical enough to allow it to be used with source and drain reversed, in this particular application. By flipping 'em around, you make the intrinsic diode work for you rather than against you. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Doing a bit of reading - this device might do the trick
http://www.linear.com/pdf/4411f.pdf Richard Richard Hosking wrote: Dear all I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Richard |
Doing a bit of reading - this device might do the trick
http://www.linear.com/pdf/4411f.pdf Richard Richard Hosking wrote: Dear all I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Richard |
Fort hose who want to see schematics, here's a web page with both the MOS
and the relay protection circuits in various versions: http://www.g4wif.fsnet.co.uk/q_tech12.htm It comes from the pages of G-QRP club. -- Sverre Holm, LA3ZA --------------------------------- www.qsl.net/la3za |
Fort hose who want to see schematics, here's a web page with both the MOS
and the relay protection circuits in various versions: http://www.g4wif.fsnet.co.uk/q_tech12.htm It comes from the pages of G-QRP club. -- Sverre Holm, LA3ZA --------------------------------- www.qsl.net/la3za |
This may need re-stating. The reverse polarity protection goes IN THE
RADIO, not the power supply. Right fellas? -- Steve N, K,9;d, c. i My email has no u's. ??? Fort Hose... ??? Cute also: When the clock gets near 12:00 I stick my head in teh co-workers office & say Djeet Jet? If the response is no, then;"Tsqueet!" "Jim Weir" wrote in message ... I'm not understanding something here. You want to design a power supply that protects against reverse voltage and overvoltage. OK. Is this power supply a battery or are you actually building a power supply that runs from the wall outlet? The requirements are quite different, depending on what you are trying to achieve. Jim Richard Hosking shared these priceless pearls of wisdom: -Dear all -I want to design a power supply for a low power rig with protection for -reverse and overvoltage. Jim Weir, VP Eng. RST Eng. WX6RST A&P, CFI, and other good alphabet soup |
This may need re-stating. The reverse polarity protection goes IN THE
RADIO, not the power supply. Right fellas? -- Steve N, K,9;d, c. i My email has no u's. ??? Fort Hose... ??? Cute also: When the clock gets near 12:00 I stick my head in teh co-workers office & say Djeet Jet? If the response is no, then;"Tsqueet!" "Jim Weir" wrote in message ... I'm not understanding something here. You want to design a power supply that protects against reverse voltage and overvoltage. OK. Is this power supply a battery or are you actually building a power supply that runs from the wall outlet? The requirements are quite different, depending on what you are trying to achieve. Jim Richard Hosking shared these priceless pearls of wisdom: -Dear all -I want to design a power supply for a low power rig with protection for -reverse and overvoltage. Jim Weir, VP Eng. RST Eng. WX6RST A&P, CFI, and other good alphabet soup |
On Sun, 11 Jan 2004 19:44:19 +0800, Richard Hosking wrote:
Dear all I want to design a power supply for a low power rig with protection for reverse and overvoltage. The requirement would be about 1A at 12-14V. What is the best way of achieving this? I guess a diode would give reverse voltage protection but the 0.6V drop is a problem. Richard Hi Richard. If you do decide to use a switching supply, the diode or diodes in the output of the switching circuit may me be all the reverse voltage protection you need. Make sure that the output smoothing capacitor can handle any voltage it is likely to encounter. A crowbar and fuse will protect against overvoltage. A hefty Thyristor (SCR or whatever they call them now) or triac makes a good crowbar. 73, Ed. EI9GQ. -- Remove 'X' to reply by E-mail. Linux 2.4.23 |
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