Electronic – Negative Voltage Converter

analogdc/dc converternegative-voltagepower supplyvoltage-regulator

I need to generate a negative voltage of approximately -12V from a 12V power supply. I read about ICL7660A that performs supply voltage conversions from positive to negative for an input range of +1.5V to +12.0V resulting in complementary output voltages of -1.5V to -12.0V. I need it to feed NE5532 OPAMPs symmetrically to perform a low pass filter, to transform a square wave into a sine wave.

However, I looked at the ICL7660A datasheet and it does not explain very much about current capacity, just a graph (datasheet Figure 7) of load current vs. output voltage. In that graph, the ICL7660A is fed by a 5V power supply and the load current seems to reach zero when output voltage reaches -5V.

Figure 7 from ICL7660A datasheet - load current vs. output voltage

(Image source: Figure 7 from ICL7660A datasheet)

I don't know exactly how much current will be required, but there are 4 NE5532 OPAMPs. I suppose that something near 50 mA is enough, no more than that.

So, I was thinking: I need -12V from a 12V power supply, is it possible? If not, is there a better approach?

Best Answer

In the datasheet the ICL7660 is measured with a load of up to 20 mA which I think will not suffice to power four NE5532 opamps

The NE5532 typically need about 8mA each.

You could make a simple circuit to generate a slightly more powerful -12 V line:

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Note that this negative rail isn't regulated and the voltage will drop when loaded.

Depending on your circuit, this could suffice, the opamps might have enough supply rejection.

If you want a "better" -12 V I would simply use an isolated DCDC converter and then connect its output such that you get a -12 V.

For example use an isolated DCDC converter like this.

There is a 5 V in to 12 V out isolated output model. Then you do need to add a voltage regulator to make +5 V from your +12 V as the DCDC converter is a boost converter, it need to start with less than 12 V.

This solution is not that efficient (some power is lost) but since your power consumption is low that should not be a serious issue.