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555 Timer Generating Negative Voltage

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Dc5e

New Member
hi, i was following this circuit http://www.csgnetwork.com/ne555c1.html and i think i know how it works... but i'm not sure if it generates enough current.

I need -5v for my 4x40 LCD, so far i've tried this circuit using slightly different valued resistors and capacitors and so far it works, but it doesn't charge/pump fast enough. Is there any way i can enhance this circuit to be able to supply more current using common parts?
 

Roff

Well-Known Member
As Russlk implies, the 555 is not ideal for this type of circuit. Even at low current loads, you lose 2 diode drops in the conversion process. The 555 also does not have a full rail-to-rail output swing, which causes you to lose even more voltage. With a 1k load, you'll probably only get about -3.6 volts. With a 100 ohm load, it might be more like -2.5 volts. This type of converter works fairly well with higher supply voltages, but for 5 volts, Russlk's suggestion is a much better solution.
 
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