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 Author Topic: how to convert 5v dc to 12v dc without using ic  (Read 11630 times) 0 Members and 1 Guest are viewing this topic.
santoshaxl
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 « on: February 16, 2011, 03:26:10 15:26 »

hi experts
i need your help i want to make 12v dc from 5v dc for 89c51 programmer . I don't want to use step up switching circuit .Is it possible from general components like diode ,zener ,capacitors etc .I think current required in 12v dc is very less .how to convert 12v from max 232 i need circuit diagram .
santo
 « Last Edit: February 16, 2011, 04:10:21 16:10 by santoshaxl » Logged
jeanninemtv
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 « Reply #1 on: February 16, 2011, 04:13:57 16:13 »

This circuit is called DC TO DC converter circuit.Which increase the voltage circuit.There can be customized to change the output values.
When the power supply input to IC1 is the output pin 3 at a frequency of 1 kHz.The frequency is Q1 and Q2, which will continue to use push pool work interchangeably.If this is the positive output signal Q1 Q2 will run the delete function this reason, C2 and C3 capacitors are half-wave alternating.
When to use. Voltage from C2 to C3 is discharged out to the input voltage over almost two times less than 2 times due to the loss of diodes D1-D3.

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oldvan
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 « Reply #2 on: February 16, 2011, 06:07:57 18:07 »

A MAX232 will only give you about 10V out at the + end of C3, per the datasheet.
http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf

The circuit above includes a 555 TIMER INTEGRATED CIRCUIT, which is what was requested not used.

If the circuit is going to have an 8-pin IC anyhow, may as well make it a MAX734 or similar and
eliminate most of the other components.
http://www.maxim-ic.com/datasheet/index.mvp/id/1548

A flyback circuit similar to this:

with the correct transformer could convert 5V to 12V with low parts count.

If noise in the circuit is the issue with a switching converter, a charge pump might be quieter, the
MAX662A, again, an IC , might do the job.

Perhaps QTY 8 AAA alkaline batteries could to the job, they'd last quite admirably for such low-current intermittent use.
 « Last Edit: February 17, 2011, 01:14:04 01:14 by oldvan » Logged

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titi
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 « Reply #3 on: February 16, 2011, 06:32:30 18:32 »

Hi,

In your case, since you have 5v, you need a voltage tripler to have 15v but with diodes you have a little less than 15v.

In this German site, you have some explanations: http://www.holger-klabunde.de/dcdc/picdcdc.htm

You can use NE555 or other oscillator with square wave or PWM 50% from microcontroler to replace 74HC14.

Best regards.
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Sideshow Bob
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 « Reply #4 on: February 16, 2011, 06:49:13 18:49 »

You can also google charge pump. And you will find many variants. A charge pump is used in PICKIT 2 and 3 to generate the programming voltage (about 14 volt I think) from a 5 volt supply. I also think the estimate on about 10 volt from a max232 is correct. Most of the time I have seen around 9 volt from a max232
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santoshaxl
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 « Reply #5 on: February 17, 2011, 02:56:00 02:56 »

i tried to convert 5 v to 12v from lm7805 regulator is this a professional method ?
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oldvan
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 « Reply #6 on: February 17, 2011, 03:58:30 03:58 »

Likely better to take your juice from the input side of the 7805, more efficient.
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