How to get negative voltage supply from +DC Voltage supply

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hi, i only got DC adapter and 78L12 and 78L05 ... how could i get a -12V and -5V from the components above? Any other circuit recommended which provide -12V and -5V from positive DC voltage source? I need it in urgent... Project due soon


Thanks a lots
 

if you want a (+) and a (-) supply in the same time, from a single positive DC adapter, then you need a switching regulator inverter, or a charge pump to get the negative voltage.
 

Re: How to get negative voltage supply from +DC Voltage supp

Hello,
Depending on what you are doing with it, you may be able to just invert your power supply. What I mean by this is using the + terminal as a ground, and the - side of your supply as your negative voltage, since voltage is relative. In many cases, you could build a supply with one 78xx regulator circuit in parallel with another, to give a + & - supply. Hope this makes sense, but if you have any questions, just ask, and I'll help.
Regards,
Robert
 

Re: How to get negative voltage supply from +DC Voltage supp

To generate low-current negative voltages you can use 555 timer IC ..
Take a look at the circuit below ..
If supplied from 12V, and without 5.1V zener diode it will generate ≈ -11V (always 1V less than positive supply) ..
With 5.1 zener diode, it will supply ≈ -5.1V ..

Regards,
IanP
 

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