Will this voltage regulator circuit work?

[larnert]

Hi guys, I'm making a voltage regulator to be plugged into a PC's PSU (as I'm fairly sure that they are fairly accurate.
Will this circuit work? - It's for a friends PICAXE which as far as I'm aware, only draws 90mA.

The reason I've got a 7809 regulator is to sort of step it down from 12v > 9v > 5v as the 78L05 which was on the PICAXE project/prototyping board, exploded 2 minutes after providing it with 12v DC from a modem power supply.

The 7809 will have a heatsink.
This diagram is a combination of two voltage regulator circuits that I've seen somewhere on the net, I also thought I would output 9v also. - just because I can.


Let me know if this will do what I'm expecting.

 

[godfreyl]

Firstly, the obvious question: Why not just use 5V from the PC power supply? IIRC, on a molex connector:
Black = ground
Red = +5V
Yellow = +12V

If you do want to go 12=>9=>5, your choice of regulators seems a little odd as the 7805 will be dissipating more heat than the 7809. It would make more sense to make both regulators "size large", with heatsinks.

 

[tpetar]

No need for this 12V-9V-5V this is not lego bricks. Voltage regulators have their specifications and conditions under which they can do the job (I mean on 10V difference range under specified temp). You can use directly 7805 regulator on 12V input with small heatsink or you can use 78S05 its 2A or 78T05 its 3A, I think 78S05 is cheaper.

You didnt say nothing about your circuit, you just say PICAXE is sharpen with some explosion.

Put that part of circuit.

 

[larnert]

Firstly, the obvious question: Why not just use 5V from the PC power supply? IIRC, on a molex connector:
Black = ground
Red = +5V
Yellow = +12V

Yeah, well, I'm revisiting electronics. Haven't done anything since I was about ...15 y/o.
You're right, the molex is 12v, ground, ground, 5v.

I sort of wanted it so I could have 9v on the same board (to eliminate the need for a 9v battery in other projects. (I'm hoping my image attached)

 

[tpetar]

Ok then for usage of 9V. But we dont see does PICAXE receive 9V or 5V ? On circuit we dont see 9V regulator ? What explode PICAXE ?

 

[larnert]

Sorry, the PICAXE microcontroller data sheet states that it should be powered with 4.5-5v and will draw 100mA.
We also thought it would be a good idea to make it a "battery eliminator" also (If other projects use a 9v battery, we can use that through the testing stages).

I'm trying to work out a way to do so without buying a variable dc voltage power supply unit.

 

[tpetar]

Sorry, the PICAXE microcontroller data sheet states that it should be powered with 4.5-5v and will draw 100mA.
We also thought it would be a good idea to make it a "battery eliminator" also (If other projects use a 9v battery, we can use that through the testing stages).

I'm trying to work out a way to do so without buying a variable dc voltage power supply unit.

Ok that for 9V regulator, but my point is for PICAXE supply voltage. AXE should receive 5V not 9V, if receive 9V maybe because that he explode.

 

[larnert]

Ok that for 9V regulator, but my point is for PICAXE supply voltage. AXE should receive 5V not 9V, if receive 9V maybe because that he explode.

Yep, the diagram has another 5v regulator.
Are those capacitors okay for that circuit?

 

[tpetar]

What is C3 value you didnt specify in circuit ?

First cap 1000uF can be 330uF and C3 should be 100nF.

Maybe you shortcut some pins on protoboard, or program bad code inside.

Did you check voltages with voltmeter?


My friend you probably reverse regulator pins check that Out/In pins.

**broken link removed**

 

[larnert]

Yea on the protoboard, it had a shape to place the regulator in, it was giving us 5v, heated up like crazy, and then when we were flashing the IC with usb, it cracked.

Also, what are the calculations for capacitors (sorry, I'm new to this and want to work it out)

 

[tpetar]

Manufacturer datasheet is relevant for proper usage of part and their configuration in circuit.

Can you post one sharpen photo of protoboard with arranged parts ?

 

[larnert]

Yep, I'll take a photo of the board for you tomorrow when I have time (at work currently)

How do you calculate what size/rating capacitors should go where?

 

[tpetar]

How do you calculate what size/rating capacitors should go where?

Manufacturer datasheet is relevant for proper usage of part and their configuration in circuit.

You can use oscilloscope to see difference with different capacitors.

Of course, because this little creatures are often used people usually knows their configuration.

 

[larnert]

So lets say, if I was to use a C1- 1000uF cap -> 7809 regulator -> C2- 100uF capacitor -> 7805(NOT 78L05) -> C3 - ****uF?

What would you recommend for C3?

Also, the lowest electrolytic capacitors I can get hold of are 25v.

 

[tpetar]

Read manufacturer datasheet.

Nominal voltage of capacitors are ok and should be higher then working voltage. Its ok to be 16V-25V for this situation.

 

[BradtheRad]

Your schematic shows a small package for the 5V regulator.

Did you also use the same small size 5V regulator the first time?

If so then it was carrying 636 mW, which is about the limit for that size part. That's why it got barbequed.
It was a resistive drop, dropping 7V at 90 mA.

 

[tpetar]

I understood that AXE exploded.

 

[godfreyl]

No. From post 1:

...the 78L05 which was on the PICAXE project/prototyping board, exploded...