Hello guys...
I am planning to make a dual voltage regulated power supply 6A +35 0 -35V
I was searching google and i stumble with this design…
My question is…
1. Whats is the purpose of transistor?
2. Is this design effective?
Interesting design, makes me want to use this in a dual voltage.
3. Can anyone pls give me a dual voltage design?
Thank you guys..

 

The transistor is used as a pass transistor to allow the circuit to provide higher current. A voltage regulator circuit with just the 78L05 is limited in how much current it can provide before overheating.

 

Sir, do you have a dual voltage design of this circuit?
Thank you..

 

I don't have any designs. But you'll want to be more specific in your requirement. Do you want a power supply that has two independent outputs?...One 0 to 35V and the other -35 to 0V? Or do you want a dual tracking supply?...One knob that adjusts the positive and negative ends at the same time?

 

1. Whats is the purpose of transistor?

It increases the current capability of the voltage regulator.

2. Is this design effective?

No. It's a terrible way to boost current because it adds a non-linear voltage drop to the regulator output.

3. Can anyone pls give me a dual voltage design?

You can do something like this with external pass transistors added to boost the current capability. But add filter caps on the input and protection diodes as desired. LM317 datasheet should give examples of current boost and discharge protection.

 

I would not use the 2N3055 or the TIP3055 because their beta (current gain) is a minimum of 20 at 4A. That means the 78L05 would
go to current limit at about 2A of load current. I would use a darlington NPN like a @2N6284 that has a beta of 750 @ 10A.
For you power supply you want to build your going to need a physical large transformer and heat sink. If you plan on a Linear supply.
For the specs you mentioned I would recommend a switching type power supply.

 

It increases the current capability of the voltage regulator.
No. It's a terrible way to boost current because it adds a non-linear voltage drop to the regulator output.

You can do something like this with external pass transistors added to boost the current capability. But add filter caps on the input and protection diodes as desired. LM317 datasheet should give examples of current boost and discharge protection.
View attachment 112803

Hi sir, can u pls give me a schematic on how to add transistors?
Thank you sir.

 

I would not use the 2N3055 or the TIP3055 because their beta (current gain) is a minimum of 20 at 4A. That means the 78L05 would
go to current limit at about 2A of load current. I would use a darlington NPN like a @2N6284 that has a beta of 750 @ 10A.
For you power supply you want to build your going to need a physical large transformer and heat sink. If you plan on a Linear supply.
For the specs you mentioned I would recommend a switching type power supply.

Got schematic sir?

 

Hi sir, can u pls give me a schematic on how to add transistors?
Thank you sir.

Most datasheets give a circuit. The one in the LM317 datasheet I referenced used LM195 for the power transistor, so I grabbed this from a 78xx datasheet. The concept is the same.


If you want to have the regulators safe area protection protect the external pass transistor, you can add a few more components and mount the regulator and pass transistor on the same heatsink; taking care to observe the signal on the cases. LM317 case is Vout, many other regulator cases are ground.

 

Hello guys...
I am planning to make a dual voltage regulated power supply 6A +35 0 -35V
I was searching google and i stumble with this design…
My question is…
1. Whats is the purpose of transistor?
2. Is this design effective?
Interesting design, makes me want to use this in a dual voltage.
3. Can anyone pls give me a dual voltage design?
Thank you guys..

Here's a start. 2N3055 gain drops as current increases, but even a gain of 6 at 6 Amps will suffice. Big heat sinks all around is suggested. The meters are optional but recommended since current limiting is weak on this design.
Engineers here could probably suggest improvements. I'm just a technician.

 

Thank you so much guys!
I learned a lot with your help.

 

If you want to set the current ratio between the regulator and pass transistor, you can use a current divider:


If you want to use a less expensive NPN power transistor, you can do this:

 

I learned a lot with your help

Don't use the external pass transistor configuration as shown in post #10. It impacts load regulation because the base-emitter voltage of the pass transistor isn't in the feedback loop. It always puzzles me why someone would do that.

 

this design…

78x05 - - does not hold up to it's specs (output power(some items have higher than 5V output(so you cant fast trim them by 2 resistors))) - - it's like you have to design a power supply and (must) use there an RND generator (78x05) ???? to make it "buzzing" / add a random noise - - to keep your regulator doing something even if there were no need for

 

78x05 - - does not hold up to it's specs

You mean they're outside of the typical 4% tolerance? Or the A suffix parts which are 2% tolerance?

Using the regulator as in the first post has an effect on load regulation. The regulator wasn't designed to minimize quiescent current change (out of the ground terminal) with load. The LM317 was designed to be used in this manner and the maximum delta Iadj is 5uA.

 

Hello guys...
I am planning to make a dual voltage regulated power supply 6A +35 0 -35V
I was searching google and i stumble with this design…
My question is…
1. Whats is the purpose of transistor?
2. Is this design effective?
Interesting design, makes me want to use this in a dual voltage.
3. Can anyone pls give me a dual voltage design?
Thank you guys..

That circuit will have lousy regulation. The appnotes suggest using a PNP pass transistor with a positive regulator. A current sensing resistor is sliced into the in lead of the 78xx. Decide what current you want in the 78xx for the transistor to start conducting - you want the resistor to drop 0.7V at the current you decide.

If you can get away with 48V; there are off the shelf SMPSU modules for telecoms equipment.

 

If you want to set the current ratio between the regulator and pass transistor, you can use a current divider:
View attachment 112833

If you want to use a less expensive NPN power transistor, you can do this:
View attachment 112834

Sir, following the schematic in fig 7.3 can i use a npn transistor for positive output voltage?

 

Sir, following the schematic in fig 7.3 can i use a npn transistor for positive output voltage?

If you want to use an NPN power transistor, you need to substitute the circuit in figure 7.4 for the power PNP.

 

If you want to use an NPN power transistor, you need to substitute the circuit in figure 7.4 for the power PNP.

I need a dual voltage power supply for my project amp sir.-35v 0 +35v
I thought i could use a 3055 and 2955 for each supply rail.
An npn for positive output and a pnp transistor for negative.

 

I need a dual voltage power supply for my project amp sir.-35v 0 +35v
I thought i could use a 3055 and 2955 for each supply rail.
An npn for positive output and a pnp transistor for negative.

Keep in mind the gain of the transistors. They drop as current increases. The regulator must be able to output enough current no matter which design you use. Regarding the two designs presented (PNP on the input or NPN on the output for a positive regulator) I couldn't say one was significantly better.