1. I would like to ask if the capacitors across the diodes are the ones' referred to as snubbers? What are the optimum values of these caps that I can use. The bridge configuration showed in the figure is made up of 4 diodes, if I will use a single brigde rectifier (those that have a "+, -, ~, ~ sign on their sides), will I still be able to use snubbers?
2. What are the advantages of using a single bridge rectifier? I saw a 35A/200V bridge diode, while the plastic diodes I use only have 6A/200V rating. Does that mean that the 35A/200V bridge has 4 diodes in one package that has a rating of 35A/200V each? Besides the current rating, is there any special reason why I must switch to a single bridge diode?
If you have any suggestions on how I can improve my amp's rectifier/filter section, feel free to modofy the figure.
Regards,
Jojo
2. What are the advantages of using a single bridge rectifier? I saw a 35A/200V bridge diode, while the plastic diodes I use only have 6A/200V rating. Does that mean that the 35A/200V bridge has 4 diodes in one package that has a rating of 35A/200V each? Besides the current rating, is there any special reason why I must switch to a single bridge diode?
If you have any suggestions on how I can improve my amp's rectifier/filter section, feel free to modofy the figure.
Regards,
Jojo
Attachments
Hi, the main bonous fo using a one piece bridge like this in a power supply is that all of the diodes in the bridge will be from the same batch and are highly likely to be VERY closely matched in tolerences to each other. You should in theory be able to draw 35 amps RMS from the bridge (so if it is a +/- supply you are driving which gives out that amount of current to that amp you should be ok), but if you do this I would sujest fastening it to a part of the metal casing, as it will have to dissipater around 35W as heat.
As far as the capacitors go, yes they are snubbers, and if you want to make them even better, you can conect a resisor in series with each capacitor. I cant remeber where I got it from but I have a PDF document on choosing the optimum values for these components, which I can post here (if I'm allowed, it's not my work), or email to you if you want it. But, be warned, it is quite deatailed, and probably has too much information for general purposes. If I were you, I would just use something like a 100Ohm resistor and a 0.1uF capacitor (you could go a bit bigger than this, but I don't think that you will see a lot of benifit from it).
As far as the capacitors go, yes they are snubbers, and if you want to make them even better, you can conect a resisor in series with each capacitor. I cant remeber where I got it from but I have a PDF document on choosing the optimum values for these components, which I can post here (if I'm allowed, it's not my work), or email to you if you want it. But, be warned, it is quite deatailed, and probably has too much information for general purposes. If I were you, I would just use something like a 100Ohm resistor and a 0.1uF capacitor (you could go a bit bigger than this, but I don't think that you will see a lot of benifit from it).
Calculating Optimum Snubbers.
Every new guy seems to need it--so here it is again.
JojoD818,
Seems like this topic is a monthly diversion around here. There are several very good links that discuss interesting power supply issues in this forum. Do a couple of searches with general power supply terminology as topics and you will probably find more information than you want.
Here is a link to one of those discussions:
Snubbers link within capacitors discussion.
Credit to Fred for first posting the link to the .pdf file.
Later,
Every new guy seems to need it--so here it is again.
JojoD818,
Seems like this topic is a monthly diversion around here. There are several very good links that discuss interesting power supply issues in this forum. Do a couple of searches with general power supply terminology as topics and you will probably find more information than you want.
Here is a link to one of those discussions:
Snubbers link within capacitors discussion.
Credit to Fred for first posting the link to the .pdf file.
Later,
It's just a starting point.
JojoD818,
You can just add the caps as shown. However, If you read the .pdf file that I provided a link for, you will see that to provide for optimum damping it is more involved than that. Not only does the snubbing capacitor have a role in the eliminiation of ringing on the supply lines, but everything both upstream and downstream of the bridge also have an effect on the action of the bridge within the supply.
It is best to build the entire amplifier and then spend some time with a good oscilloscope looking at your supply rails and bridge to determine how much capacitance and resistance you need to add to snub the ringing produced by the bridge's diodes. Damping of circuits is almost always a function of resistance and in this case that is our intention.
You can guess at these values beforehand but the most accurate way is to measure the ringing, calculate the appropriate capacitance and resistance, and apply them appropriately to the circuit.
Later,
JojoD818,
You can just add the caps as shown. However, If you read the .pdf file that I provided a link for, you will see that to provide for optimum damping it is more involved than that. Not only does the snubbing capacitor have a role in the eliminiation of ringing on the supply lines, but everything both upstream and downstream of the bridge also have an effect on the action of the bridge within the supply.
It is best to build the entire amplifier and then spend some time with a good oscilloscope looking at your supply rails and bridge to determine how much capacitance and resistance you need to add to snub the ringing produced by the bridge's diodes. Damping of circuits is almost always a function of resistance and in this case that is our intention.
You can guess at these values beforehand but the most accurate way is to measure the ringing, calculate the appropriate capacitance and resistance, and apply them appropriately to the circuit.
Later,
sam9
Depemds on if you are building a power amp or something like a pre-amp that just process and switches signals.
Yes these are snubbers.
In a power amp the rectifier diodes tend to get a bit warm, so some heatsinking is called for. The Bridge rectifiers with a metal case (25A or 35A) are very convenient in this respect since bolting them to the bottom of the enclosure takes care of the heatsinking. I solder a cap (.01uF - .1uF, 250+V) between each pair of tabs around the perifery and then solder the power leads. There are usualy a pair of holes in the tabs you can thread to make this fairly simple.
In a pre/processor, heat is not much of an issue so you can make your own bridge on a PCB and construct a more elaborate snubbing network that includes both a resistor in series with the diodes and a cap parrallel. See the technical articals www.hagtech.com for how to calculate the optimum values for the resistors and caps.
In my opinion the more elaborate snubbing network is not required in a power amp unless the design has a rather modest PSRR. In preamps and processors, the audio signal is smaller and more subject to picking up noise so extra efforst to clean up the rails is worthwhile.
PS: never seen a truly convincing reason for two bridges unless is is to compensate for a design compromise elsewhere. Again, that's just IMHO.
Depemds on if you are building a power amp or something like a pre-amp that just process and switches signals.
Yes these are snubbers.
In a power amp the rectifier diodes tend to get a bit warm, so some heatsinking is called for. The Bridge rectifiers with a metal case (25A or 35A) are very convenient in this respect since bolting them to the bottom of the enclosure takes care of the heatsinking. I solder a cap (.01uF - .1uF, 250+V) between each pair of tabs around the perifery and then solder the power leads. There are usualy a pair of holes in the tabs you can thread to make this fairly simple.
In a pre/processor, heat is not much of an issue so you can make your own bridge on a PCB and construct a more elaborate snubbing network that includes both a resistor in series with the diodes and a cap parrallel. See the technical articals www.hagtech.com for how to calculate the optimum values for the resistors and caps.
In my opinion the more elaborate snubbing network is not required in a power amp unless the design has a rather modest PSRR. In preamps and processors, the audio signal is smaller and more subject to picking up noise so extra efforst to clean up the rails is worthwhile.
PS: never seen a truly convincing reason for two bridges unless is is to compensate for a design compromise elsewhere. Again, that's just IMHO.
Transformer protection.
Although a little off-topic, I though I wou;d mention the practice of putting fuses between the bridge rectifier and the transformer. The reason is that bridges can (even if rarely) fail and that failure maybe be in the form of creating a short circuit. This will quickly destroy the transformer. Considering the relative cost of transformers and fusers, you might think abot this.
Although a little off-topic, I though I wou;d mention the practice of putting fuses between the bridge rectifier and the transformer. The reason is that bridges can (even if rarely) fail and that failure maybe be in the form of creating a short circuit. This will quickly destroy the transformer. Considering the relative cost of transformers and fusers, you might think abot this.
Re: Transformer protection.
A properly sized fuse on the primary side of the transformer should take care of this. The transformer can withstand the short long enough to blow the fuse (if sized correctly)...
-Dan
sam9 said:
A properly sized fuse on the primary side of the transformer should take care of this. The transformer can withstand the short long enough to blow the fuse (if sized correctly)...
-Dan
Guys,
Thanks for the replies especially the links. After those explanation, and instructions from sam and the rest of the group, I got what I need. Tomorrow I'll treat my power amp with a brand new bridge diode and snubber. Let's see what happens 😉
Jojo
Thanks for the replies especially the links. After those explanation, and instructions from sam and the rest of the group, I got what I need. Tomorrow I'll treat my power amp with a brand new bridge diode and snubber. Let's see what happens 😉
Jojo
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