Breadboard Power Supply

Ok, you got your soldering iron and nothing is going to hold you back, but you have no clue where to start or what to build. There were others before you with the same questions... read them first.
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DrNomis
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Post by DrNomis »

jstbrowsin wrote:Thanks Pokey Pete and Dr Nomis for your input. Most appreciated.
I guess I should have been more specific with my info, the caps that blow are the C1 & C2 and they are rated at 63V, in turn they also blow the 2N3055 T03 transistors that have a huge heatsink. The LM317's are T package and there are no heat sink's attached :oops: but I can remedy this 8) . The filter caps are rated at 75V so I think they should be safe too eh.

Ok so going on your advice I change the LM317T in the neg supply to LM337T and add heat sinks.
Would it also be advisable to double the size of resistance (R1-R2) to slow the current and save the transistors and everything else?

DrNomis wrote: I also noticed that,if the two outputs ate connected to obtain positive and negative supplies,the ground connection will be floating..... :)

Pray do tell how can I remedy this please?



Thanks again for all you help guys :)

75V Caps will be fine as the filter caps,I tend to over-rate the components for the job when I design circuits,makes them more reliable..... :)


The best way to remedy the floating-earth issue,is to use a single Bridge-Rectifier circuit,you have a power transformer in your schematic that has a centre tap,connect this centre tap to ground,as in the schematic I posted,and use the other two terminals to feed the Bridge-Rectifier,the transformer Centre-Tap also becomes the ground reference for the rest of the power supply circuit,note that you then have to use the LM317/337T combination to regulate the supply rails,not two LM317Ts,the LM317/337T Adjustable regulators are rated for a maximum of about 1.5A,so to "boost" the current output capability of the power supply,you can use a 2N3055 and an MJ2955 connected as a series-pass transistor,these transistors are in TO-3 packages and are rated for a maximum collector current of 15A I believe,I'll post a schematic showing how to connect them as series-pass transistors..... :)
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Post by DrNomis »

Here's the schematic for adding series-pass current boosting transistors,the only downside is that you have to be very careful not to short either the positive or negative outputs directly to ground,otherwise the two series-pass transistors wil self-destruct at the speed of light...ie,instantly.... :)

I must work out some way to incorporate short-circuit protection.... :)
Attachments
Series Pass Transistors Schematic
Series Pass Transistors Schematic
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Post by jstbrowsin »

Thanks again Dr Nomis for sorting out the floating ground. :D

I do appreciate your design schematic for adding "series-pass current boosting transistors" however is this really necessary for me as 15A seems way to excessive for a breadboard to me anyhow. And am I seeing clearly it looks like there are 3.3Ω 15W resistors on the input of the regulators, or should they really be 5W?


So my list now is as follows:
Change the LM317T in the neg supply to LM337T.
Add heat sinks.
Remove one of the recitfiers and put centre tap in ground position as per schem.

Have I got everything right here? Do I need to do anything else to stabilize the circuit? Am I good to go?

thanks again guys :applause:

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Post by DrNomis »

jstbrowsin wrote:Thanks again Dr Nomis for sorting out the floating ground. :D

I do appreciate your design schematic for adding "series-pass current boosting transistors" however is this really necessary for me as 15A seems way to excessive for a breadboard to me anyhow. And am I seeing clearly it looks like there are 3.3Ω 15W resistors on the input of the regulators, or should they really be 5W?


So my list now is as follows:
Change the LM317T in the neg supply to LM337T.
Add heat sinks.
Remove one of the recitfiers and put centre tap in ground position as per schem.

Have I got everything right here? Do I need to do anything else to stabilize the circuit? Am I good to go?

thanks again guys :applause:

Yeah,I agree,15A is way too excessive for a breadboard power supply,but,the 15A rating of the series-pass transistors means that you can use a 3 A power transformer and not blow the regulators,I would still include them if I was using a 500mA power transformer too,I was designing for reliability,since the regulators aren't over-dissipating,and the last thing you want is the power supply going faulty just as you're testing a circuit out.... :)


Those 3.3 Ohm resistors are 5 Watt ceramic wire-wound types,they are probably a bit over-rated for the job,but I decided to use them anyway.... :)

Apart from that,your list looks all good to go,feel free to download the schematics I posted,and use them for your power supply,hope it all goes well,any problems feel free to let me know.... :)
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Post by jstbrowsin »

Ah that makes more sense cheers mate. . .

so I should change my transistors? I have 2 in parallel for each supply oops I guess I should have mentioned that before.

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DrNomis
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Post by DrNomis »

jstbrowsin wrote:Ah that makes more sense cheers mate. . .

so I should change my transistors? I have 2 in parallel for each supply oops I guess I should have mentioned that before.

You really only need 1 MJ2955 for the positive supply rail,and 1 2N3055 for the negative power supply rail,as per the schematic,one of each is ample enough.... :)


The 2N3055 is an NPN Si Bipolar Power Transistor,and the MJ2955 is a PNP Si Bipolar Power Transistors with the same specs as the 2N3055,except that it is a PNP device,of course.... :)
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.

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