|
power transistor for PS. what to uses?
Hi everyone I have made a power supply for my rigs
The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao |
"Deos" wrote in message ... Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . The function of the pass transistor is to dissipate as heat the difference between input and output. Sounds like you need a bigger heat sink...or build a switching supply. Ray |
"Deos" wrote in message ... Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . The function of the pass transistor is to dissipate as heat the difference between input and output. Sounds like you need a bigger heat sink...or build a switching supply. Ray |
Hi, check this link and see what you need to do,
one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? regards, clarke Deos wrote: Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao |
Hi, check this link and see what you need to do,
one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? regards, clarke Deos wrote: Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao |
clarke wrote:
Hi, check this link and see what you need to do, one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? regards, clarke Deos wrote: Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob |
clarke wrote:
Hi, check this link and see what you need to do, one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? regards, clarke Deos wrote: Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob |
Hi everyone I have made a power supply for my rigs
The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? ======== Assuming that so far you have only considered bi-polar transistors ,perhaps it would be beneficial to look into the application of Power MOSFETs. In the 'on' state they have a very low resistance ,hence at high currents they dissipate less heat . Consequently you would need smaller heat sinks. Frank GM0CSZ / KN6WH |
Hi everyone I have made a power supply for my rigs
The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? ======== Assuming that so far you have only considered bi-polar transistors ,perhaps it would be beneficial to look into the application of Power MOSFETs. In the 'on' state they have a very low resistance ,hence at high currents they dissipate less heat . Consequently you would need smaller heat sinks. Frank GM0CSZ / KN6WH |
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote:
If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! -- "Windows [n.], A thirty-two bit extension and GUI shell to a sixteen bit patch to an eight bit operating system originally coded for a four bit microprocessor and produced by a two bit company." |
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote:
If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! -- "Windows [n.], A thirty-two bit extension and GUI shell to a sixteen bit patch to an eight bit operating system originally coded for a four bit microprocessor and produced by a two bit company." |
Paul Burridge wrote:
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! 2N3055 are great, but 2N3771 are better! Rob |
Paul Burridge wrote:
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! 2N3055 are great, but 2N3771 are better! Rob |
the trasformer is in the KW range.....
it's a big nasty beast. -- http://www.qsl.net/sv1hao "clarke" wrote in message ... Hi, check this link and see what you need to do, one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? regards, clarke Deos wrote: Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao |
the trasformer is in the KW range.....
it's a big nasty beast. -- http://www.qsl.net/sv1hao "clarke" wrote in message ... Hi, check this link and see what you need to do, one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? regards, clarke Deos wrote: Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? -- http://www.qsl.net/sv1hao |
dont have any idea how to work with mosfet
any links in the right direction? -- http://www.qsl.net/sv1hao "Frank Dinger" wrote in message ... Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? ======== Assuming that so far you have only considered bi-polar transistors ,perhaps it would be beneficial to look into the application of Power MOSFETs. In the 'on' state they have a very low resistance ,hence at high currents they dissipate less heat . Consequently you would need smaller heat sinks. Frank GM0CSZ / KN6WH |
dont have any idea how to work with mosfet
any links in the right direction? -- http://www.qsl.net/sv1hao "Frank Dinger" wrote in message ... Hi everyone I have made a power supply for my rigs The schematic is the typical regulator with power transistor wrapped around it for the extra juice. I need 40 amps continues .. I tried 4 mj2955 which are rather nice for foot warming in the winter . I also tried nte-180 which are very good. is there anything better at a logical price I would like to keep the number of transistors down to 1 or 2. Can someone advise my on what to use for power? ======== Assuming that so far you have only considered bi-polar transistors ,perhaps it would be beneficial to look into the application of Power MOSFETs. In the 'on' state they have a very low resistance ,hence at high currents they dissipate less heat . Consequently you would need smaller heat sinks. Frank GM0CSZ / KN6WH |
On Mon, 20 Oct 2003 20:28:06 GMT, Jim Higgins
wrote: The basic design demonstrates a generally acceptable approach to designing a power suppy, but some of the components chosen just don't seem up to meeting the design criteria of 24 volts in, 12 volts out at 30 amps. Such designs are simply brain dead. If you need +12 V at 30 A and you are using NPN series pass transistors, you should use about 13 V at the end of the capacitor discharge cycle. This should be doable with far less than 24 V capacitor nominal voltage. Assuming the capacitor voltage drops from say 17 V to 13 V during each half cycle, the power dissipation in the series pass transistors will be ((17+13)/2 V)-12 V) x 30 A or 90 W, so this is doable with 3-6 transistors. However, the required base voltage varies between 14 and 18 V, so a separate power supply is required, either with a separate secondary winding or by using some kind of voltage doubling, but this needs to supply only 2-4 A. The other alternative is to use PNP series pass transistors on the +12 V side, in which case a high, separate voltage is not needed. Paul OH3LWR |
On Mon, 20 Oct 2003 20:28:06 GMT, Jim Higgins
wrote: The basic design demonstrates a generally acceptable approach to designing a power suppy, but some of the components chosen just don't seem up to meeting the design criteria of 24 volts in, 12 volts out at 30 amps. Such designs are simply brain dead. If you need +12 V at 30 A and you are using NPN series pass transistors, you should use about 13 V at the end of the capacitor discharge cycle. This should be doable with far less than 24 V capacitor nominal voltage. Assuming the capacitor voltage drops from say 17 V to 13 V during each half cycle, the power dissipation in the series pass transistors will be ((17+13)/2 V)-12 V) x 30 A or 90 W, so this is doable with 3-6 transistors. However, the required base voltage varies between 14 and 18 V, so a separate power supply is required, either with a separate secondary winding or by using some kind of voltage doubling, but this needs to supply only 2-4 A. The other alternative is to use PNP series pass transistors on the +12 V side, in which case a high, separate voltage is not needed. Paul OH3LWR |
Assuming that so far you have only considered bi-polar transistors perhaps
it would be beneficial to look into the application of Power MOSFETs. In the 'on' state they have a very low resistance ,hence at high currents they dissipate less heat . Consequently you would need smaller heat sinks. dont have any idea how to work with mosfet In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. It's true that modern power MOSFETs have a very low series resistance when switched "fully on". This allows for low losses, and relatively low heat dissipation, if they're used in an application where "fully on, or fully off" is suitable. "Hard" power switching, or pulse- width-modulated drive applications such as a switching regulator or a DC motor-speed controller are good places for MOSFETs (or IGBTs). However, a linear regulator isn't this sort of application. In these regulators, you aren't driving the pass transistor "hard on" - because, if you did, the regulator would simply pass the full input voltage to its output and wouldn't regulate at all! Instead, you're switching the transistor on only partway, so that it's passing only the amount of current needed to "pull up" the outputs to the regulation voltage. The rest of the voltage (input minus output) is going to appear across the pass transistor (and possibly one or two other components in series with it, such as ballast resistors) and will be dissipated as heat. This will be true regardless of whether the regulating element is a MOSFET, bipolar transistor, or whatever. If you're sucking 30 amperes, and dropping 10 volts between input and output, your pass elements will be dissipating 300 watts. The only ways I know of to reduce the heat dissipation are to either lower your input voltage (but not enough to cause the circuit to drop out of regulation), or move to a lower-loss architecture such as a buck-mode switching regulator. The latter can be quite efficient (often 90% or better), but you have to work REALLY HARD to build one which won't emit enough radiated and conducted RF switching noise to totally yngvi up your HF reception. I agree with the other posters, who suggest that it's probably preferable to use a sufficient number of simple, easy-to-buy pass transistors (2N3055 being the classic example). Use enough so that you can use 'em well within conservative ratings - don't go anywhere near the edge of the "safe operating area" - and ballast them so that they share current properly. -- 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! |
Assuming that so far you have only considered bi-polar transistors perhaps
it would be beneficial to look into the application of Power MOSFETs. In the 'on' state they have a very low resistance ,hence at high currents they dissipate less heat . Consequently you would need smaller heat sinks. dont have any idea how to work with mosfet In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. It's true that modern power MOSFETs have a very low series resistance when switched "fully on". This allows for low losses, and relatively low heat dissipation, if they're used in an application where "fully on, or fully off" is suitable. "Hard" power switching, or pulse- width-modulated drive applications such as a switching regulator or a DC motor-speed controller are good places for MOSFETs (or IGBTs). However, a linear regulator isn't this sort of application. In these regulators, you aren't driving the pass transistor "hard on" - because, if you did, the regulator would simply pass the full input voltage to its output and wouldn't regulate at all! Instead, you're switching the transistor on only partway, so that it's passing only the amount of current needed to "pull up" the outputs to the regulation voltage. The rest of the voltage (input minus output) is going to appear across the pass transistor (and possibly one or two other components in series with it, such as ballast resistors) and will be dissipated as heat. This will be true regardless of whether the regulating element is a MOSFET, bipolar transistor, or whatever. If you're sucking 30 amperes, and dropping 10 volts between input and output, your pass elements will be dissipating 300 watts. The only ways I know of to reduce the heat dissipation are to either lower your input voltage (but not enough to cause the circuit to drop out of regulation), or move to a lower-loss architecture such as a buck-mode switching regulator. The latter can be quite efficient (often 90% or better), but you have to work REALLY HARD to build one which won't emit enough radiated and conducted RF switching noise to totally yngvi up your HF reception. I agree with the other posters, who suggest that it's probably preferable to use a sufficient number of simple, easy-to-buy pass transistors (2N3055 being the classic example). Use enough so that you can use 'em well within conservative ratings - don't go anywhere near the edge of the "safe operating area" - and ballast them so that they share current properly. -- 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! |
rob34 wrote:
Paul Burridge wrote: On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! 2N3055 are great, but 2N3771 are better! Rob True, but you can find 2N3055, or house numbered versions for free in a lot of old linear power supplies pulled from junked equipment. -- Michael A. Terrell Central Florida |
rob34 wrote:
Paul Burridge wrote: On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! 2N3055 are great, but 2N3771 are better! Rob True, but you can find 2N3055, or house numbered versions for free in a lot of old linear power supplies pulled from junked equipment. -- Michael A. Terrell Central Florida |
On Mon, 20 Oct 2003 19:33:02 +0100, Paul Burridge
wrote: On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! The main reason I wouldn't use a 2N3055 in that application is the gain falls of dramatically at high Ic. Design needs to accommodate this in terms of both driver current capability and loop gain. |
On Mon, 20 Oct 2003 19:33:02 +0100, Paul Burridge
wrote: On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: If you want to keep it to a couple transistors they would be expensive. You are better off using either more NTE-180 or more mj2955, but I would cut the voltage down to around 18 volts instead of 24 volts as this higher voltage leads to more heat for the transistors. Rob How come no one's yet recommeded that great old PSU war-horse, the 2N3055? Six of them on a decent heat sink and you're sorted! The main reason I wouldn't use a 2N3055 in that application is the gain falls of dramatically at high Ic. Design needs to accommodate this in terms of both driver current capability and loop gain. |
Dave Platt wrote: In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. . . . Someone mentioned the 2 to 4 amps of base current you'd have to supply for bipolar pass transistors. You wouldn't need it if you used FETs. I'd look seriously at P-channel VMOS for pass devices, myself. Roy Lewallen, W7EL |
Dave Platt wrote: In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. . . . Someone mentioned the 2 to 4 amps of base current you'd have to supply for bipolar pass transistors. You wouldn't need it if you used FETs. I'd look seriously at P-channel VMOS for pass devices, myself. Roy Lewallen, W7EL |
Hi, from Ken,
"rob34" wrote in message ... Paul Burridge wrote: On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: 2N3055 are great, but 2N3771 are better! Rob 2N3773 are better still ( check out current ). If you want a power supply to deliver round about 40amps the the first thing to remember is that you MUST have the correct amount of pass transistors to handle the current. If you use 2N3055's ( very good and cheap ) you will need at least 10 of these, don't think for one minute becouse you see the current stated as being 20amps that one transistor will be able to handle this amout of current, it won't, it does not work like that. The best you can hope for ( current wise ) from one 2N3055 is FIVE AMPS. So for a forty amp supply you would need at least, eight and a couple for that le-way we all try to allow. One other thing you must have good heat sinks. Regards the transformer, it should be able to handle the current and should ( ideally for a 13.8Volt supply ) be rated between 17.5 and 18.5 Volts of load. Once regulated this voltage will rise to about, 24 Volts + or - 1 or 2 Volts. Regards regulation the most common way is to use the LM723 voltage regulator chip complete with short circuit protection. Smoothing caps should be another point of concern. Try to find two large ripple handling units rated at about 40 Volts and allow two thousand mfd per one amp of current required. One final point to remember when building your own power supply is to use some form of ELECTRONIC OVER-VOLTAGE PROTECTION ( I.e., the MC3423 chip is perfect ). The number of cheap commercial power supplies on the market without overvoltage protection fitted is a crime ( but they never tell you this in the Ads..right..?. ). Hope the above helps in some small way. Good luck, Ken, G4KIR. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.525 / Virus Database: 322 - Release Date: 09/10/2003 |
Hi, from Ken,
"rob34" wrote in message ... Paul Burridge wrote: On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote: 2N3055 are great, but 2N3771 are better! Rob 2N3773 are better still ( check out current ). If you want a power supply to deliver round about 40amps the the first thing to remember is that you MUST have the correct amount of pass transistors to handle the current. If you use 2N3055's ( very good and cheap ) you will need at least 10 of these, don't think for one minute becouse you see the current stated as being 20amps that one transistor will be able to handle this amout of current, it won't, it does not work like that. The best you can hope for ( current wise ) from one 2N3055 is FIVE AMPS. So for a forty amp supply you would need at least, eight and a couple for that le-way we all try to allow. One other thing you must have good heat sinks. Regards the transformer, it should be able to handle the current and should ( ideally for a 13.8Volt supply ) be rated between 17.5 and 18.5 Volts of load. Once regulated this voltage will rise to about, 24 Volts + or - 1 or 2 Volts. Regards regulation the most common way is to use the LM723 voltage regulator chip complete with short circuit protection. Smoothing caps should be another point of concern. Try to find two large ripple handling units rated at about 40 Volts and allow two thousand mfd per one amp of current required. One final point to remember when building your own power supply is to use some form of ELECTRONIC OVER-VOLTAGE PROTECTION ( I.e., the MC3423 chip is perfect ). The number of cheap commercial power supplies on the market without overvoltage protection fitted is a crime ( but they never tell you this in the Ads..right..?. ). Hope the above helps in some small way. Good luck, Ken, G4KIR. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.525 / Virus Database: 322 - Release Date: 09/10/2003 |
Thanks Jim for posting the flaws in that design !
Here is a better schematic http://www.wa8dbw.ifip.com/rs-70a.gif for an Astron 70a linear ps. clarke Jim wrote: On Mon, 20 Oct 2003 13:57:46 GMT, in , clarke wrote: Hi, check this link and see what you need to do, one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? I'm not sure anyone has ever built the PSU shown at the above URL, and if so, I'd guess they haven't run it at the full 30-amp output for more than a few seconds. The basic design demonstrates a generally acceptable approach to designing a power suppy, but some of the components chosen just don't seem up to meeting the design criteria of 24 volts in, 12 volts out at 30 amps. The ballast resistors are rated at 1 watt, but will be expected to dissipate roughly 2.5 watts at the full 30-amp output. The text analyzing the regulator performance has me baffled. It correctly describes a current gain of about 35 for the pass transistors, which at a glance suggests the regulator has to handle a bit under 1 amp. The web page author says 871 ma is the current into the regulator input and 866 ma is the current out, for a net current of 5 ma and a cool regulator. Looks to me like that poor thing is going to be asked to dissipate about 10 watts and will run about 110 degrees C even if mounted on an *infinite* heat sink. I'd redesign to include a transistor driver. I'd say the designer of this supply never ran it at full output for more than a few seconds. -- Jim Higgins, KB3PU Help for prospective and new hams, see: http://groups.yahoo.com/group/HAM-ELMER Elmers also welcome |
Thanks Jim for posting the flaws in that design !
Here is a better schematic http://www.wa8dbw.ifip.com/rs-70a.gif for an Astron 70a linear ps. clarke Jim wrote: On Mon, 20 Oct 2003 13:57:46 GMT, in , clarke wrote: Hi, check this link and see what you need to do, one or two pass trans. will not do the job for you, easier to use 6-10 pass trans to share the load. http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm Is your transformer able to supply necessary power to this supply ? I'm not sure anyone has ever built the PSU shown at the above URL, and if so, I'd guess they haven't run it at the full 30-amp output for more than a few seconds. The basic design demonstrates a generally acceptable approach to designing a power suppy, but some of the components chosen just don't seem up to meeting the design criteria of 24 volts in, 12 volts out at 30 amps. The ballast resistors are rated at 1 watt, but will be expected to dissipate roughly 2.5 watts at the full 30-amp output. The text analyzing the regulator performance has me baffled. It correctly describes a current gain of about 35 for the pass transistors, which at a glance suggests the regulator has to handle a bit under 1 amp. The web page author says 871 ma is the current into the regulator input and 866 ma is the current out, for a net current of 5 ma and a cool regulator. Looks to me like that poor thing is going to be asked to dissipate about 10 watts and will run about 110 degrees C even if mounted on an *infinite* heat sink. I'd redesign to include a transistor driver. I'd say the designer of this supply never ran it at full output for more than a few seconds. -- Jim Higgins, KB3PU Help for prospective and new hams, see: http://groups.yahoo.com/group/HAM-ELMER Elmers also welcome |
Dave Platt wrote:
In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. . . . Someone mentioned the 2 to 4 amps of base current you'd have to supply for bipolar pass transistors. Good point. The base current wouldn't be wasted (it'd flow into the load), but the need for a fairly high-current driver would certainly complicate the circuitry and require the use of a higher-voltage transformer and unregulated supply, compared to a MOSFET solution. You wouldn't need it if you used FETs. I'd look seriously at P-channel VMOS for pass devices, myself. Might be even more advantageous to use N-channel VMOS, and regulate on the negative side of the load. N-channel power MOSFETs are significantly less expensive than the closest P-channel equivalents, and there seems to be quite a bit more choice in terms of size and rating. If I recall properly, the charge-carrier mobility in an N channel (electrons) is a good deal higher than in a P channel (holes), which means that N-channel MOSFETs can have smaller channel areas than equivalent P-channel devices, hence more dice per wafer, hence lower prices. -- 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! |
Dave Platt wrote:
In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. . . . Someone mentioned the 2 to 4 amps of base current you'd have to supply for bipolar pass transistors. Good point. The base current wouldn't be wasted (it'd flow into the load), but the need for a fairly high-current driver would certainly complicate the circuitry and require the use of a higher-voltage transformer and unregulated supply, compared to a MOSFET solution. You wouldn't need it if you used FETs. I'd look seriously at P-channel VMOS for pass devices, myself. Might be even more advantageous to use N-channel VMOS, and regulate on the negative side of the load. N-channel power MOSFETs are significantly less expensive than the closest P-channel equivalents, and there seems to be quite a bit more choice in terms of size and rating. If I recall properly, the charge-carrier mobility in an N channel (electrons) is a good deal higher than in a P channel (holes), which means that N-channel MOSFETs can have smaller channel areas than equivalent P-channel devices, hence more dice per wafer, hence lower prices. -- 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! |
Dave Platt wrote:
Dave Platt wrote: In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. . . . Someone mentioned the 2 to 4 amps of base current you'd have to supply for bipolar pass transistors. Good point. The base current wouldn't be wasted (it'd flow into the load), but the need for a fairly high-current driver would certainly complicate the circuitry and require the use of a higher-voltage transformer and unregulated supply, compared to a MOSFET solution. You wouldn't need it if you used FETs. I'd look seriously at P-channel VMOS for pass devices, myself. Might be even more advantageous to use N-channel VMOS, and regulate on the negative side of the load. N-channel power MOSFETs are significantly less expensive than the closest P-channel equivalents, and there seems to be quite a bit more choice in terms of size and rating. If I recall properly, the charge-carrier mobility in an N channel (electrons) is a good deal higher than in a P channel (holes), which means that N-channel MOSFETs can have smaller channel areas than equivalent P-channel devices, hence more dice per wafer, hence lower prices. I built a cheap ps using a bunch of 2n3055's as pass transistors. (think I had 5 or 6 of them in parallel). Each had a 0.1 ohm resistor in the emitter lead to balance out the current (or one might try to hog it all if the transistors aren't well matched). They well darlington connected to another 2n3055 which acted as a driver (and helps increase the gain at high collector current). Yet another transistor was used to drive the driver (TO-5 si, probably a 2n3053 or equal) from the regulator IC. A large heat sink was used and I mounted surplus computer power supply fans on it to add cooling. I used a heavy transformer and the input voltage to the pass regulator was about 15-16 volts for 13.6 out. Key here is that with a large transformer and enough filter C the voltage won't droop on high current (guess that means it's well regulated without the regulator!) , and we don't ask the transistors to disapate too much power. Course' such a supply is HEAVY, a switcher is much lighter, but a good switcher with low noise is hard to come by! (Not to mention problems of rf feed back!). |
Dave Platt wrote:
Dave Platt wrote: In this particular application - pass transistors in a linear regulator - I don't see that MOSFETs would have any particular advantage. . . . Someone mentioned the 2 to 4 amps of base current you'd have to supply for bipolar pass transistors. Good point. The base current wouldn't be wasted (it'd flow into the load), but the need for a fairly high-current driver would certainly complicate the circuitry and require the use of a higher-voltage transformer and unregulated supply, compared to a MOSFET solution. You wouldn't need it if you used FETs. I'd look seriously at P-channel VMOS for pass devices, myself. Might be even more advantageous to use N-channel VMOS, and regulate on the negative side of the load. N-channel power MOSFETs are significantly less expensive than the closest P-channel equivalents, and there seems to be quite a bit more choice in terms of size and rating. If I recall properly, the charge-carrier mobility in an N channel (electrons) is a good deal higher than in a P channel (holes), which means that N-channel MOSFETs can have smaller channel areas than equivalent P-channel devices, hence more dice per wafer, hence lower prices. I built a cheap ps using a bunch of 2n3055's as pass transistors. (think I had 5 or 6 of them in parallel). Each had a 0.1 ohm resistor in the emitter lead to balance out the current (or one might try to hog it all if the transistors aren't well matched). They well darlington connected to another 2n3055 which acted as a driver (and helps increase the gain at high collector current). Yet another transistor was used to drive the driver (TO-5 si, probably a 2n3053 or equal) from the regulator IC. A large heat sink was used and I mounted surplus computer power supply fans on it to add cooling. I used a heavy transformer and the input voltage to the pass regulator was about 15-16 volts for 13.6 out. Key here is that with a large transformer and enough filter C the voltage won't droop on high current (guess that means it's well regulated without the regulator!) , and we don't ask the transistors to disapate too much power. Course' such a supply is HEAVY, a switcher is much lighter, but a good switcher with low noise is hard to come by! (Not to mention problems of rf feed back!). |
| All times are GMT +1. The time now is 03:57 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com