How to use simple circuit to converter +5V to -5V

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mag

Joined: 05 May 2004
Posts: 41

15 Jul 2004 0:55 How to use simple circuit to converter +5V to -5V

My systerm all are +5V supply,But now have a amp circuit need -5V+-10%---10mA supply,how can I use a simple circuit to converter +5V to -5V.the special charge pump chip all are expensive,I only need a simple circuit.

ITP

Joined: 11 Jul 2001
Posts: 110

15 Jul 2004 4:39 How to use simple circuit to converter +5V to -5V

See this link

/http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm

Regards
Itp

emmos

Joined: 30 Dec 2003
Posts: 61
Helped: 2

15 Jul 2004 6:15 Re: How to use simple circuit to converter +5V to -5V

Hi everybody

i think u can just use the LM7905 regulator to get the -5V as u use LM7805 to get the +5V

hope this helps u
bye
emmos

mag

Joined: 05 May 2004
Posts: 41

15 Jul 2004 6:46 Re: How to use simple circuit to converter +5V to -5V

Sorry,My systerm only have +5V DC source,so I can not use 7905 to generate -5VDC.

ynhe

Joined: 28 May 2001
Posts: 326
Helped: 4
Location: China

15 Jul 2004 6:56 Re: How to use simple circuit to converter +5V to -5V

Hi
Use CMOS Charge Pump Inverter if output current is not high,such as cat660,max660.

ynhe

Ozonehole2k

Joined: 25 Mar 2004
Posts: 31

15 Jul 2004 6:58 Re: How to use simple circuit to converter +5V to -5V

Quote:

i think u can just use the LM7905 regulator to get the -5V as u use LM7805 to get the +5V

LM7905 is yet another linear regulator. You still need a negative voltage to start with. Also, note the voltage drop of these device is not insignificant. In general, use a +7V unregulated supply if you are going to make +5V regulated with 7805; -7V unregulated to make -5V regulated.

There are switchmode power supply ICs that handles the conversion. You can also try more common ICs like MAX232 (yes, the level converter for serial port, 0-5V in => +/- 15V out) or some 555 timer based homebrew switchmode.

hxxttp://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm

leemarrow

Joined: 03 May 2001
Posts: 294
Helped: 1

15 Jul 2004 8:10 Re: How to use simple circuit to converter +5V to -5V

here a simple converter using icl7660

Sorry, but you need login in to view this attachment

neelandan

Joined: 26 Mar 2004
Posts: 28
Helped: 1
Location: Terra Firma

15 Jul 2004 10:17 How to use simple circuit to converter +5V to -5V

Assuming your main circuit is digital, there might be a clock there somewhere. Run it to a spare buffer, and connect a voltage doubler circuit to its output, for a negative voltage (two diodes and two capacitors). Depending on the load, the voltage might come to somewhat above 5 volts.

rauol

Joined: 02 Oct 2002
Posts: 363
Helped: 11

15 Jul 2004 11:58 Re: How to use simple circuit to converter +5V to -5V

Use a timer 555 as a voltage inverter it will be very cheap at low powers

nebisman

Joined: 13 Apr 2002
Posts: 291
Helped: 1

15 Jul 2004 15:15 Re: How to use simple circuit to converter +5V to -5V

The best solutio is to use a charge pump ICL 7660 as described below. This integrated circuit costs less than US 1 thne isn't so expensive. If you want to do it by yourself you can use a digital CMOS buffer as 74HC245 oscillator and capacitors. You can also use a buck converter using a low cost pwm regulator as LM3524 from national.

nebisman

mag

Joined: 05 May 2004
Posts: 41

16 Jul 2004 1:30 Re: How to use simple circuit to converter +5V to -5V

for such suggest,i think 555 is best method.
max660, ICL 7660 also are a good select,but the cost is expansiver than 555.

my project:
use this -5V for amp offset adjusting,and resolution is 300uV,so afraid ripple of 555 circuit will be too large for this application.

rauol

Joined: 02 Oct 2002
Posts: 363
Helped: 11

17 Jul 2004 14:47 Re: How to use simple circuit to converter +5V to -5V

try using LC filters

alphi

Joined: 23 Dec 2001
Posts: 440
Helped: 1

17 Jul 2004 17:03 Re: How to use simple circuit to converter +5V to -5V

LC filter can not filter all noise,special for switching power supply.

rauol

Joined: 02 Oct 2002
Posts: 363
Helped: 11

18 Jul 2004 9:27 Re: How to use simple circuit to converter +5V to -5V

Maxim and LT have some regulators which offer very low noise

adi-niunio

Joined: 11 Jul 2004
Posts: 3

18 Jul 2004 11:04 Re: How to use simple circuit to converter +5V to -5V

Ozonehole2k wrote:

There are switchmode power supply ICs that handles the conversion. You can also try more common ICs like MAX232 (yes, the level converter for serial port, 0-5V in => +/- 15V out)

I don't how big current you need, but maybe you can use max232 to have -15V and then use lm7905 to have -5V no the output Smile