Generating -5VDC from +5VDC
Generating -5VDC from +5VDC(From Richard Friesen)
If you happen to have the March 1984 issue of Radio-Electronics, turn to page 78. This issue has the very first instalment of Robert Grossblatt's "Designer's Notebook" column. In it, he shows a simple circuit which will supply a negative voltage, given a positive voltage. It's basically a 555-based oscillator, and a voltage-doubling rectifier. He claims the negative-voltage output should be good for about 60ma. No-load voltage should be pretty close to the input voltage (but negative), although the voltage will drop a bit, depending on the load. If you put +5V into the circuit, it'll give you around -5V out. load. If you put +5V into the circuit, it'll give you around -5V out. If the load makes the voltage drop too low (-3V or -4V), you could always just feed the circuit with a higher voltage (like maybe 9V or 12V) and then just regulate the output down to -5V using a 7905 regulator. I've used this circuit a couple of times for powering op-amp's, and it works great!
I'm not that great at ASCII-art, but I'll give it a shot. If the following schematic doesn't make sense, let me know, and I'll try it again...
+V ^ | +-------+---+ | | | -V Output R1 |8 |4 +----+---> | 7 ------- | | Parts List: +-----| | D2 | IC1 = 555 | +--| | + | | R1 = 1.5K R2 | 6| IC1 |---C1--+ | R2 = 10K | | | |3 | | C1 = 10uF,16V +--+--| | D1 C2 C2 = 22uF,16V | 2| | | |+ C3 = 1500pF | ------- | | D1,D2 = 1N4001 diodes C3 |1 | | | | | | +---------+-----------+----+ | === (GND)
Note: In the above "diagram", both diodes point down (the anodes are at the top). Also, watch the polarity of C1 & C3.
The circuit is set up to oscillate at about 45kHz, with a duty cycle pretty close to 50%. None of the values of any of the parts are terribly critical, so if the capacitors or resistors are "in the ballpark", it should still work okay.