Description.
This circuit diagram shows how to obtain a negative voltage from a positive voltage supply. Another advantage of this circuit is that, the negative voltage together with the original positive supply can be used to simulate a dual supply. The circuit is based on timer IC NE555. The NE555 is wired as an astable multivibrator operating at around 1 KHz. The square wave output if available at pin no 3 of the IC. During the positive half of the square wave, capacitor C3 charges through diode D2.When the output of IC is at zero the C3 discharges through diode D2 and the capacitor C4 gets charged. As a result of this the voltage at the junction of the anode of D1 and cathode of C4 will be always negative with respect to the ground.
Circuit diagram.

Notes.

• Assemble the circuit on a Vero board.
• The IC1 must be mounted on a holder.
• C3 and C4 must be rated at least 25V.
• Do not connect loads that consume more than 50mA current.
• The negative voltage output will be always a few volts lower than the positive supply.

#### 6 Comments

1. If you increase c3 to 33uf you will get -11.97v. 12v in and almost -12v out

2. i tried it on multisim but output port of ic burns as i run the circuit

3. millionbit

Can i use a 7905 to the output to regulate the voltage?

4. Please anyone can make me understand, why we need this circuit. In my understanding its easy to just reverse the polarity of existing (so called +12 volt) supply.
I think there must be some reason that one need this circuit, thats what I want to understand.

• Seetharaman

Hi Fayaz you are correct but when we require both + and _ voltage like opamp supply you have only one 12 volt rechargeable battery supply, this circuit will be useful to produce -12 volt from+12 volt hence you will have +12 – 0 – -12volt supply.

5. Wonderful circuit, I was needing some similar to feed my voltimeter and that fits my needs perfectly. Congratulations for posting this circuit! I was struggling with a 7905 and that 555 inverter resolved my issue.