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#1
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In article
, "Pete KE9OA" wrote: Snip Somebody made a comment about how cool the Icom R-75 runs..........I bet that you haven't attempted to touch that internal 5V regulator. There have been some failures with this regulator recently. The failure mechanism is caused by the fact that Icom chose to use an 18V supply to power the radio. Dave Zantos has modified his power supply by adding a pre-regulator that brings the voltage down to 13.5V before it enters the radio. My advice? Either modify that Icom power brick or replace it with a regulated 13.5V power supply. Looking inside of that supply, you will find spots on the circuit board for adding bypass caps across each rectifier diode. Add .01uF caps in these places and it will prevent the diodes from rectifying RF. Another good mod for this power supply is to add a 1uF NP cap from each leg of the SECONDARY of the power transformer to ground. This snubs the switching noise from the rectifier diodes. I have heard mention on this NG that purchasing a good regulated supply gets rid of these emissions........this is not really the case. Any power supply can be made quiet by using the aforementioned techniques. The AOR7030s power supply can also benefit from these mods. You are right about the 5V regulator. These are series regulator elements and the higher the input voltage the more power they must dissipate to regulate the voltage down to the lower voltage. People don't seem to get the diode rectifier concept here though. The diode in the power supply passes current when the voltage polarity is in the right direction and blocks it in the reverse. This is the rectification function. When the diode switched from on to off the circuit goes to high impedance. This results in a voltage spike that can damage the diode if the voltage goes above the PIV rating. PIV stands for Peak Inverse Voltage. It is this voltage spike every time the diode switches off that causes EMI/RFI depending on the path. It could be either or both but is usually mostly EMI. If it is mostly EMI, the usual case, then a common mode choke will block the majority of the diode switching noise on the cord to the radio. The power supply terminology to reduce the PIV voltage across the diode so as to not damage it is a "snubber" circuit. This is usually made of a cap and resistor across the diode. The cap/resistor time constant value is determined by the duration of the reverse spike it design to absorb. The resistor burns the power. If the spike is small and you want to suppress it for RF reasons only then it can be just a cap. The capacitor will circulate the current from the voltage spike around the diode, which is a small RF current loop, instead of allowing it to propagate away from the diode through the rest of the power supply circuit up the power cord and into your radio and make a buzz at 60 or 120 Hz. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. -- Telamon Ventura, California |
#2
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Telamon wrote:
In article , "Pete KE9OA" wrote: Snip Somebody made a comment about how cool the Icom R-75 runs..........I bet that you haven't attempted to touch that internal 5V regulator. There have been some failures with this regulator recently. The failure mechanism is caused by the fact that Icom chose to use an 18V supply to power the radio. Dave Zantos has modified his power supply by adding a pre-regulator that brings the voltage down to 13.5V before it enters the radio. My advice? Either modify that Icom power brick or replace it with a regulated 13.5V power supply. Looking inside of that supply, you will find spots on the circuit board for adding bypass caps across each rectifier diode. Add .01uF caps in these places and it will prevent the diodes from rectifying RF. Another good mod for this power supply is to add a 1uF NP cap from each leg of the SECONDARY of the power transformer to ground. This snubs the switching noise from the rectifier diodes. I have heard mention on this NG that purchasing a good regulated supply gets rid of these emissions........this is not really the case. Any power supply can be made quiet by using the aforementioned techniques. The AOR7030s power supply can also benefit from these mods. You are right about the 5V regulator. These are series regulator elements and the higher the input voltage the more power they must dissipate to regulate the voltage down to the lower voltage. People don't seem to get the diode rectifier concept here though. The diode in the power supply passes current when the voltage polarity is in the right direction and blocks it in the reverse. This is the rectification function. When the diode switched from on to off the circuit goes to high impedance. This results in a voltage spike that can damage the diode if the voltage goes above the PIV rating. A voltage spike occurs when interrupting power to an inductive load. There is no indictive load in what you are describing. PIV stands for Peak Inverse Voltage. It is this voltage spike every time the diode switches off that causes EMI/RFI depending on the path. It could be either or both but is usually mostly EMI. If it is mostly EMI, the usual case, then a common mode choke will block the majority of the diode switching noise on the cord to the radio. The power supply terminology to reduce the PIV voltage across the diode so as to not damage it is a "snubber" circuit. This is usually made of a cap and resistor across the diode. The cap/resistor time constant value is determined by the duration of the reverse spike it design to absorb. The resistor burns the power. A snubber circuit is used to protect a driver from the transient when switching power to an inductive load. See, http://focus.ti.com/lit/an/slup100/slup100.pdf The radio power supply is not that type of circuit. If the spike is small and you want to suppress it for RF reasons only then it can be just a cap. The capacitor will circulate the current from the voltage spike around the diode, which is a small RF current loop, instead of allowing it to propagate away from the diode through the rest of the power supply circuit up the power cord and into your radio and make a buzz at 60 or 120 Hz. The diode is acting as a mixer. It is combining the 60 Hz line voltages and the signals at the radio frequencies creating a signal at RF with a large 60Hz modulation. Adding a cap bypasses the diode at RF, significantly reducing the mixing action. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. You need a complete circuit for current to flow. At 60 Hz, what is the rest of the circuit? It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. I suggest looking at the whole picture and look at what this does at 60 Hz and at RF frequencies. Later, Craigm |
#3
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In article , craigm
wrote: Telamon wrote: In article , "Pete KE9OA" wrote: Snip Somebody made a comment about how cool the Icom R-75 runs..........I bet that you haven't attempted to touch that internal 5V regulator. There have been some failures with this regulator recently. The failure mechanism is caused by the fact that Icom chose to use an 18V supply to power the radio. Dave Zantos has modified his power supply by adding a pre-regulator that brings the voltage down to 13.5V before it enters the radio. My advice? Either modify that Icom power brick or replace it with a regulated 13.5V power supply. Looking inside of that supply, you will find spots on the circuit board for adding bypass caps across each rectifier diode. Add .01uF caps in these places and it will prevent the diodes from rectifying RF. Another good mod for this power supply is to add a 1uF NP cap from each leg of the SECONDARY of the power transformer to ground. This snubs the switching noise from the rectifier diodes. I have heard mention on this NG that purchasing a good regulated supply gets rid of these emissions........this is not really the case. Any power supply can be made quiet by using the aforementioned techniques. The AOR7030s power supply can also benefit from these mods. You are right about the 5V regulator. These are series regulator elements and the higher the input voltage the more power they must dissipate to regulate the voltage down to the lower voltage. People don't seem to get the diode rectifier concept here though. The diode in the power supply passes current when the voltage polarity is in the right direction and blocks it in the reverse. This is the rectification function. When the diode switched from on to off the circuit goes to high impedance. This results in a voltage spike that can damage the diode if the voltage goes above the PIV rating. A voltage spike occurs when interrupting power to an inductive load. There is no indictive load in what you are describing. PIV stands for Peak Inverse Voltage. It is this voltage spike every time the diode switches off that causes EMI/RFI depending on the path. It could be either or both but is usually mostly EMI. If it is mostly EMI, the usual case, then a common mode choke will block the majority of the diode switching noise on the cord to the radio. The power supply terminology to reduce the PIV voltage across the diode so as to not damage it is a "snubber" circuit. This is usually made of a cap and resistor across the diode. The cap/resistor time constant value is determined by the duration of the reverse spike it design to absorb. The resistor burns the power. A snubber circuit is used to protect a driver from the transient when switching power to an inductive load. See, http://focus.ti.com/lit/an/slup100/slup100.pdf The radio power supply is not that type of circuit. The snubber protects the rectifier diode from the transformer and series inductors in the power supply LC output filtering. There is a reason why most diodes have a PIV much higher than the voltage in the circuits they operate in. Ever wonder why? If the spike is small and you want to suppress it for RF reasons only then it can be just a cap. The capacitor will circulate the current from the voltage spike around the diode, which is a small RF current loop, instead of allowing it to propagate away from the diode through the rest of the power supply circuit up the power cord and into your radio and make a buzz at 60 or 120 Hz. The diode is acting as a mixer. It is combining the 60 Hz line voltages and the signals at the radio frequencies creating a signal at RF with a large 60Hz modulation. Adding a cap bypasses the diode at RF, significantly reducing the mixing action. Thanks for writing that. The reason I have written this now overly long thread is to explain the reason for by passing and how it works and why the thinking that the diode is switching RF ground on and off is generating the noise is rubbish. You should connect an oscilloscope to a power supply rectifier diode in operation. If you would do that you will see a large voltage spike based on the inductance of the circuit and how fast the diode switches. Faster diodes are more efficient but the spike voltage will increase with the faster switch time so faster diodes will need a higher PIV rating. A fairly slow diode switching at 60 or 120 Hz depending on the rectifier circuit in a low current supply may not develop a very high PIV so a capacitor by itself may do the job. Low current supplies likely have slower diodes because the heat they dissipate results from the product of the switch time and current going through them. Larger supplies will have more current through the diodes and so that they don't burn up they have to switch faster. Bigger supplies have bigger inductors and faster diodes with larger PIV as a result. Switching more power means you need a snubber RC across the diode instead of just a capacitor. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. You need a complete circuit for current to flow. At 60 Hz, what is the rest of the circuit? One side of the capacitor is grounded through the AC mains ground lead and on the other side is alternating voltage at 60 Hz. It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. I suggest looking at the whole picture and look at what this does at 60 Hz and at RF frequencies. I did and have. It is common practice to use a small value capacitor to ground on or near the power supply outputs where any common mode noise from switching transients is coupled to ground. You can do this at the transformer secondary but why generate the 60 Hz current if you don't have to do that? The object is to conduct noise currents to ground not 60 Hz mains supply. -- Telamon Ventura, California |
#4
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The diode is acting as a mixer. It is combining the 60 Hz line voltages and the signals at the radio frequencies creating a signal at RF with a large 60Hz modulation. Adding a cap bypasses the diode at RF, significantly reducing the mixing action. Thanks for writing that. The reason I have written this now overly long thread is to explain the reason for by passing and how it works and why the thinking that the diode is switching RF ground on and off is generating the noise is rubbish. I didn't say anything about switching RF ground......................I said that the diode is radiating the noise. You should connect an oscilloscope to a power supply rectifier diode in operation. If you would do that you will see a large voltage spike based on the inductance of the circuit and how fast the diode switches. Faster diodes are more efficient but the spike voltage will increase with the faster switch time so faster diodes will need a higher PIV rating. A fairly slow diode switching at 60 or 120 Hz depending on the rectifier circuit in a low current supply may not develop a very high PIV so a capacitor by itself may do the job. Low current supplies likely have slower diodes because the heat they dissipate results from the product of the switch time and current going through them. Larger supplies will have more current through the diodes and so that they don't burn up they have to switch faster. Bigger supplies have bigger inductors and faster diodes with larger PIV as a result. The mechanism I am talking about isn't isolated to just high current supplies, unless you are talking about a 200mA supply as being high current. Switching more power means you need a snubber RC across the diode instead of just a capacitor. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. At 60Hz, a 1uF cap has a considerable amount of capacitive reactance, so very little current would go through this loop. You need a complete circuit for current to flow. At 60 Hz, what is the rest of the circuit? One side of the capacitor is grounded through the AC mains ground lead and on the other side is alternating voltage at 60 Hz. It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. I suggest looking at the whole picture and look at what this does at 60 Hz and at RF frequencies. I did and have. It is common practice to use a small value capacitor to ground on or near the power supply outputs where any common mode noise from switching transients is coupled to ground. You can do this at the transformer secondary but why generate the 60 Hz current if you don't have to do that? The object is to conduct noise currents to ground not 60 Hz mains supply. -- Telamon Ventura, California |
#5
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In article ,
"Pete KE9OA" wrote: The diode is acting as a mixer. It is combining the 60 Hz line voltages and the signals at the radio frequencies creating a signal at RF with a large 60Hz modulation. Adding a cap bypasses the diode at RF, significantly reducing the mixing action. Thanks for writing that. The reason I have written this now overly long thread is to explain the reason for by passing and how it works and why the thinking that the diode is switching RF ground on and off is generating the noise is rubbish. I didn't say anything about switching RF ground......................I said that the diode is radiating the noise. Yeah, that was someone else responding to my response to your post. I hope that makes sense. You should connect an oscilloscope to a power supply rectifier diode in operation. If you would do that you will see a large voltage spike based on the inductance of the circuit and how fast the diode switches. Faster diodes are more efficient but the spike voltage will increase with the faster switch time so faster diodes will need a higher PIV rating. A fairly slow diode switching at 60 or 120 Hz depending on the rectifier circuit in a low current supply may not develop a very high PIV so a capacitor by itself may do the job. Low current supplies likely have slower diodes because the heat they dissipate results from the product of the switch time and current going through them. Larger supplies will have more current through the diodes and so that they don't burn up they have to switch faster. Bigger supplies have bigger inductors and faster diodes with larger PIV as a result. The mechanism I am talking about isn't isolated to just high current supplies, unless you are talking about a 200mA supply as being high current. Not 200mA. Things don't get interesting until you are above a few amps. Switching more power means you need a snubber RC across the diode instead of just a capacitor. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. At 60Hz, a 1uF cap has a considerable amount of capacitive reactance, so very little current would go through this loop. Well, that depends on the secondary voltage. A few tens of volts would generate current in the milli amp range, which is not a lot but it's not necessary. You need a complete circuit for current to flow. At 60 Hz, what is the rest of the circuit? One side of the capacitor is grounded through the AC mains ground lead and on the other side is alternating voltage at 60 Hz. It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. I suggest looking at the whole picture and look at what this does at 60 Hz and at RF frequencies. I did and have. It is common practice to use a small value capacitor to ground on or near the power supply outputs where any common mode noise from switching transients is coupled to ground. You can do this at the transformer secondary but why generate the 60 Hz current if you don't have to do that? The object is to conduct noise currents to ground not 60 Hz mains supply. -- Telamon Ventura, California -- Telamon Ventura, California |
#6
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I remember...........you have come up with some pretty good ideas about this
subject in the past. Thanks! Pete "Telamon" wrote in message ... In article , "Pete KE9OA" wrote: Snip Somebody made a comment about how cool the Icom R-75 runs..........I bet that you haven't attempted to touch that internal 5V regulator. There have been some failures with this regulator recently. The failure mechanism is caused by the fact that Icom chose to use an 18V supply to power the radio. Dave Zantos has modified his power supply by adding a pre-regulator that brings the voltage down to 13.5V before it enters the radio. My advice? Either modify that Icom power brick or replace it with a regulated 13.5V power supply. Looking inside of that supply, you will find spots on the circuit board for adding bypass caps across each rectifier diode. Add .01uF caps in these places and it will prevent the diodes from rectifying RF. Another good mod for this power supply is to add a 1uF NP cap from each leg of the SECONDARY of the power transformer to ground. This snubs the switching noise from the rectifier diodes. I have heard mention on this NG that purchasing a good regulated supply gets rid of these emissions........this is not really the case. Any power supply can be made quiet by using the aforementioned techniques. The AOR7030s power supply can also benefit from these mods. You are right about the 5V regulator. These are series regulator elements and the higher the input voltage the more power they must dissipate to regulate the voltage down to the lower voltage. People don't seem to get the diode rectifier concept here though. The diode in the power supply passes current when the voltage polarity is in the right direction and blocks it in the reverse. This is the rectification function. When the diode switched from on to off the circuit goes to high impedance. This results in a voltage spike that can damage the diode if the voltage goes above the PIV rating. PIV stands for Peak Inverse Voltage. It is this voltage spike every time the diode switches off that causes EMI/RFI depending on the path. It could be either or both but is usually mostly EMI. If it is mostly EMI, the usual case, then a common mode choke will block the majority of the diode switching noise on the cord to the radio. The power supply terminology to reduce the PIV voltage across the diode so as to not damage it is a "snubber" circuit. This is usually made of a cap and resistor across the diode. The cap/resistor time constant value is determined by the duration of the reverse spike it design to absorb. The resistor burns the power. If the spike is small and you want to suppress it for RF reasons only then it can be just a cap. The capacitor will circulate the current from the voltage spike around the diode, which is a small RF current loop, instead of allowing it to propagate away from the diode through the rest of the power supply circuit up the power cord and into your radio and make a buzz at 60 or 120 Hz. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. -- Telamon Ventura, California |
#7
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No problem. I used to work on switching power supply designs.
In article , "Pete KE9OA" wrote: I remember...........you have come up with some pretty good ideas about this subject in the past. Thanks! Pete "Telamon" wrote in message .. . In article , "Pete KE9OA" wrote: Snip Somebody made a comment about how cool the Icom R-75 runs..........I bet that you haven't attempted to touch that internal 5V regulator. There have been some failures with this regulator recently. The failure mechanism is caused by the fact that Icom chose to use an 18V supply to power the radio. Dave Zantos has modified his power supply by adding a pre-regulator that brings the voltage down to 13.5V before it enters the radio. My advice? Either modify that Icom power brick or replace it with a regulated 13.5V power supply. Looking inside of that supply, you will find spots on the circuit board for adding bypass caps across each rectifier diode. Add .01uF caps in these places and it will prevent the diodes from rectifying RF. Another good mod for this power supply is to add a 1uF NP cap from each leg of the SECONDARY of the power transformer to ground. This snubs the switching noise from the rectifier diodes. I have heard mention on this NG that purchasing a good regulated supply gets rid of these emissions........this is not really the case. Any power supply can be made quiet by using the aforementioned techniques. The AOR7030s power supply can also benefit from these mods. You are right about the 5V regulator. These are series regulator elements and the higher the input voltage the more power they must dissipate to regulate the voltage down to the lower voltage. People don't seem to get the diode rectifier concept here though. The diode in the power supply passes current when the voltage polarity is in the right direction and blocks it in the reverse. This is the rectification function. When the diode switched from on to off the circuit goes to high impedance. This results in a voltage spike that can damage the diode if the voltage goes above the PIV rating. PIV stands for Peak Inverse Voltage. It is this voltage spike every time the diode switches off that causes EMI/RFI depending on the path. It could be either or both but is usually mostly EMI. If it is mostly EMI, the usual case, then a common mode choke will block the majority of the diode switching noise on the cord to the radio. The power supply terminology to reduce the PIV voltage across the diode so as to not damage it is a "snubber" circuit. This is usually made of a cap and resistor across the diode. The cap/resistor time constant value is determined by the duration of the reverse spike it design to absorb. The resistor burns the power. If the spike is small and you want to suppress it for RF reasons only then it can be just a cap. The capacitor will circulate the current from the voltage spike around the diode, which is a small RF current loop, instead of allowing it to propagate away from the diode through the rest of the power supply circuit up the power cord and into your radio and make a buzz at 60 or 120 Hz. You can use a cap to the AC outlet ground on the secondary side of the transformer but it might not be the best thing to do as it or a pair on either side on the secondary will generate a continuous current down the AC mains ground lead at 60 Hz. It might be better to use one cap on the negative side of the DC output to ground in order to reduce this common mode switch noise. Alternatively you might try a cap on the positive output to ground in addition to the one one the negative side. Here you will only be sending the noise currents down the AC mains leads and not the 60Hz components. -- Telamon Ventura, California -- Telamon Ventura, California |
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