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Author Topic: REQ: Need circuit for PIC supply, 5V and 3.3V  (Read 3555 times)
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iphone
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« on: July 02, 2010, 12:09:42 12:09 »

Hi guys,

Need your help. I design a PIC voltage supply using IC MC34063 for PIC using proteus but fail to get good/stable 5V output from the circuit. Maybe someone can comment or share the working circuit here. Also please share for 3.3V using the same IC.

My proteus file as per attached.

tq

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« Reply #1 on: July 02, 2010, 05:39:52 17:39 »

Hi,

In your design, the value for C2 is too important, use 470pF and it works well.

Best Regards.
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« Reply #2 on: July 02, 2010, 08:00:31 20:00 »

You can have a look here, This is a little tool to help you. You can calculate the output voltage

http://www.nomad.ee/micros/mc34063a/index.shtml
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« Reply #3 on: July 14, 2010, 07:18:10 07:18 »

I built the 5v step down from datasheet schematic. It is working fine on my PIC.
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« Reply #4 on: July 31, 2010, 02:44:31 14:44 »

I do not know of this problem is solved already for iphone?

titi is right, wrong capacitor.

The mc34063a is used in lot of network routers/switches,
i drawed the schematic of some and i found:

A resistor between pin 7 and 8, value 220E to 470E (collector resistor)
(When pin 7 and 8 connected together, i blowed up some devices in development phase,
my application pulls 140 mA current)
This was for me the solution everything works fine.

Other hint: take R2 and R3 low, pulls some more current but
gives better feedback (R2/R3 U-divider) for voltage stability.
(see component LM317T for example)






« Last Edit: July 31, 2010, 02:57:17 14:57 by blauwhaar » Logged
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« Reply #5 on: August 01, 2010, 05:18:47 05:18 »

I've built it and it's successful using 470pF.

But in one of my project, using transformer 230VAC - 24AC (50Amps), the IC (34063) and other IC (PIC16F877A, LM358, LM324 been blow (short circuit) but LM7810 (3 pin regulator work ok).

The 34063 is direct connect to 24AC after bridge rectifier n cap ( I think cap bigger than 4700 uF) but LM7810 is connect to 24VAC (after brideg rectifier n cap) via 10 ohm 2W resister and LM7810 safe but 34063 been blow (short) also PIC16F877A which connect to 34063. Why, anybody can explain? or mc34063 is need to use in carefull manner or using battery only ?

tq guys.
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« Reply #6 on: August 01, 2010, 09:56:02 21:56 »

iphone,

seems, you've made some mistake in your pcb.

Look here:
http://radiohlam.ru/pitanie/preobr_down.htm

That page is on Russian, but you will find working circuit diagram very similar with yours. Look on it to be sure.

I have made the same circuit many times for +5V applications.

I can give you an advice. As you do not need 500 mA output current, try to set R1 (in your circuit diagram) as 1.5 Ohm - it will limit the output current on 100 mA. It will be enough to protect IC surely.
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« Reply #7 on: August 03, 2010, 01:12:53 01:12 »

You can have a look here, This is a little tool to help you. You can calculate the output voltage

http://www.nomad.ee/micros/mc34063a/index.shtml
good find so I made a *.exe copy for off line work.


http://rapidshare.com/files/410680081/MC24063-Calc.rar.html <400k
« Last Edit: August 03, 2010, 02:04:19 02:04 by pickit2 » Logged

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« Reply #8 on: August 03, 2010, 01:50:21 01:50 »

rar is corrupted Pickit
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« Reply #9 on: August 03, 2010, 08:00:16 08:00 »

good find so I made a *.exe copy for off line work.


http://rapidshare.com/files/410680081/MC24063-Calc.rar.html <400k

Thanks for Exe.

I have one suggestion, maybe you can attach/include the sample of circuit (working 100%) of fix 12V, fix 5V n 3.3V because it's hard for me ( in beginning) to set any data/value as no reference to experiment on.

btw, thanks a lot for conversion.
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« Reply #10 on: August 03, 2010, 12:57:53 12:57 »

Only problem I found with Calc id the value of the inductor, most time gives a odd value.
To make a working project, this what I did, I had some known inductors 220uH and 100uH. I used the calc to find components I needed to get the output voltage I needed.
I then used proteus to test the ciruit values as given by calc. (which was very close in proteus to what was given) I then replaced the inductor in proteus to one of the ones I have in parts bin. and ajusted values of Ct and R1, R2 (one at a time to get the voltage I needed)
Then built pcb in real life.
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« Reply #11 on: August 03, 2010, 05:11:27 17:11 »

iphone,
You can use this LMZ14202 for your design. This is a 2A SIMPLE SWITCHER® Power Module with 42V Maximum Input

Electrical Specifications
12W maximum total output power
Up to 2A output current
Input voltage range 6V to 42V
Output voltage range 0.8V to 6V
Efficiency up to 90%

And you can use the Webench Power Designer for obtain the Schematic design, Bill of materials, etc.

Overview: http://www.national.com/pf/LM/LMZ14202.html#Overview
Datasheet: http://www.national.com/ds/LM/LMZ14202.pdf
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« Reply #12 on: August 03, 2010, 05:51:21 17:51 »

Have you checked the price of a LMZ14202 lately, I don't think anyone here is going to spend that much unless it's a very very special project
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« Reply #13 on: August 15, 2010, 07:24:35 19:24 »

I've built it and it's successful using 470pF.

But in one of my project, using transformer 230VAC - 24AC (50Amps), the IC (34063) and other IC (PIC16F877A, LM358, LM324 been blow (short circuit) but LM7810 (3 pin regulator work ok).


The 34063 is direct connect to 24AC after bridge rectifier n cap ( I think cap bigger than 4700 uF) but LM7810 is connect to 24VAC (after brideg rectifier n cap) via 10 ohm 2W resister and LM7810 safe but 34063 been blow (short) also PIC16F877A which connect to 34063. Why, anybody can explain? or mc34063 is need to use in carefull manner or using battery only ?

tq guys.

I hope you didn`t use diode as in your picture (1N5711) because it is low current diode. Use UF4007 for 500mA and up to 300V or 1N5822 for up to 40V and 3A. They are bigger but you have no problems with heat.

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