DC power supply

[vick5821]

Hey friends, I plan to build a DC power supply for my future usage of electricity to replace battery.

I plan to use the adapter(Approximate 16 -18V) as input and I plan to use voltage regulators too -- 7805, 7806, 7809, and 7812( Common source of voltage)

My concept is like this :

I plan to have a DC power supply and a switch so that I can adjust to the voltage output that I need. For eg, I want 9V, so I make the 9V available by adjusting the switch. What most important is, I plan to have only ONE output terminal and not 4 output terminal(As it will be messy) So it means when I want 6V , I adjust it to be 6V at the output. And when I want 9V, I adjust it to be 9V that will be appearing at the output terminal

This is my initial sketch of my circuit :

In this sketch, I will add diode 4007 before the Vin of the regulator and PLAN TO ADD 4007 diode too at the Vout of regulator. But placing diode in the Vout of regulator cause me one problem - Diode has voltage drop of apporximate 0.7V. This means when the Vout is 5V, the exact voltage at the output terminal will be only around 4.3V.

Any ideas on how to overcome this and any more suggestion on implementing this DC power supply circuit ?

Thank you

 

[scmong]

You may try by connecting one diode, like 1N4007, between the middle leg of each Regulator IC and negative line. Thanks.

 

[CocaCola]

Use a DPDT switch to switch the supply and output at the same time...

 

[gorgon]

You should really take care and use a diode on alle the outputs, to separate them. To compensate for the diode loss use the same type of diode in the ground lead, to increase the voltages accordingly, In fact a single diode connected to all the regulators should be ok.

Not all types of regulators like back voltage in on the output, and certainly not a higher voltage than it's own, so a diode on each output is necessary.

I don't think you'll need a diode on the Vin side. Even less necessary if you use a selector switch.

The best would be to use a 2pole selector, selecting both input and output to/ from each regulator. Then you don't need diodes either.

Remember to rate the capacitors on the output after the highest voltage available.

TOK

 

[vick5821]

Use a DPDT switch to switch the supply and output at the same time...

Why DPDT ? I think DPST is enough already ? One connected to the Vin and one connected to the Vout ?

 

[vick5821]

You should really take care and use a diode on alle the outputs, to separate them. To compensate for the diode loss use the same type of diode in the ground lead, to increase the voltages accordingly, In fact a single diode connected to all the regulators should be ok.

Not all types of regulators like back voltage in on the output, and certainly not a higher voltage than it's own, so a diode on each output is necessary.

I don't think you'll need a diode on the Vin side. Even less necessary if you use a selector switch.

The best would be to use a 2pole selector, selecting both input and output to/ from each regulator. Then you don't need diodes either.

Remember to rate the capacitors on the output after the highest voltage available.

TOK

I will be using 10 microFarad, 25V electroltic capacitor at the Vin and Vout. Do you think it is ok ?

 

[CocaCola]

Why DPDT ? I think DPST is enough already ? One connected to the Vin and one connected to the Vout ?

Fool proof, no diodes and no worries about back feeding or whatever...

 

[vick5821]

oh.If I used DPST, it will have the back feeding phenomena because I used only only output terminal ?

 

[vick5821]

Bear in mind that my project consist of 4 output voltages ( 5V, 6V, 9V AND 12V)

 

[CocaCola]

Well then you need a 2p4t

 

[vick5821]

Hahaha. Is it possible to implement it using 4 DPST switch to switch on the input and the respective output together ?

 

[CocaCola]

Hahaha. Is it possible to implement it using 4 DPST switch to switch on the input and the respective output together ?

I'm sure with enough switches you could find some way of doing it, but remember if the all the inputs and outputs don't switch in sync it defeats the entire purpose, and you won't save anything...

2p4t switches are easy (and cheap) enough to source, in both slide and rotary styles and you will have no complications or worries...

 

[vick5821]

I'm sure with enough switches you could find some way of doing it, but remember if the all the inputs and outputs don't switch in sync it defeats the entire purpose, and you won't save anything...

2p4t switches are easy (and cheap) enough to source, in both slide and rotary styles and you will have no complications or worries...

What do you mean by the bolded part ?

Thank you

 

[vick5821]

I'm sure with enough switches you could find some way of doing it, but remember if the all the inputs and outputs don't switch in sync it defeats the entire purpose, and you won't save anything...

2p4t switches are easy (and cheap) enough to source, in both slide and rotary styles and you will have no complications or worries...

By the way, I dont think I am able to find a DP4T switch here . Why not I implment it using four switch since I have 4 type of output voltage ? looks more organised instead ?

 

[vick5821]

Fool proof, no diodes and no worries about back feeding or whatever...

How if I build using two DPDT switch with 4 regulator ? I just do what you draw but I double it to become two same circuit ? Good idea ?

btw, I think I have to put some smoothing capacittor like 10uF, 25V for the Vin side as my voltage input is type of unregulated power supply ? The output perhaps just put another one ? Any suggestion ?

 

[CocaCola]

If you use individual switches you risk going back to your original issue where you might have two regulators on at the same time an have the two outputs collide... You could glue all the slides together into one unit and avoid issues like this, I just see you going uphill when there is a simple downhill solution...

I dont think I am able to find a DP4T switch here

Have you looked? I find irony in that since I live in the US and have sourced components direct from manufactures in Malaysia, and even outsourced some PC board manufacturing to Malaysia...

 

[vick5821]

If you use individual switches you risk going back to your original issue where you might have two regulators on at the same time an have the two outputs collide... You could glue all the slides together into one unit and avoid issues like this, I just see you going uphill when there is a simple downhill solution...



Have you looked? I find irony in that since I live in the US and have sourced components direct from manufactures in Malaysia, and even outsourced some PC board manufacturing to Malaysia...

Anyway, I plan to have combinational output isnt that good idea also ?

 

[vick5821]

Lateset sketch. Is it ok ?

 

[Rleo6965]

Hi Vick,

Try this simple circuit. You can use only 1 pc IC voltage regulator. Place heatsink on LM317.

 

[vick5821]

you mean I have to use 4 potentiometer and adjust them in proper position to get 5V, V , 9V and 12V respectively at the outputt ? Or replaceed it with fixed value resistor ?