In my application, I want to generate -9V/50mA from 12V Input. What are options available?

I have come across few options as below:

1) http://www.ti.com/lit/an/slva257a/slva257a.pdf

Buck regulator to generate -ve output by changing OUTPUT and GND pins. For such low load current, possibility is that it will operate in DCM mode.

2) Dual Pump Charge Output http://www.farnell.com/datasheets/9917.pdf

I need IC which will take and generate -9V.

  • \$\begingroup\$ There are plenty of DC/DC converters, for example this one that will give you +9V and -9V from +12V. Do you have some particular need (like package size)? \$\endgroup\$ – Roger Rowland Aug 9 '16 at 6:21
  • \$\begingroup\$ As well as what Roger said, you can use an isolated 12V:9V DC-DC and just ground the + output. \$\endgroup\$ – Spehro Pefhany Aug 9 '16 at 6:26
  • \$\begingroup\$ What use would negative 9v be? \$\endgroup\$ – Alex Aug 9 '16 at 8:55
  • \$\begingroup\$ for op-amp and ADC application. \$\endgroup\$ – Electroholic Aug 9 '16 at 8:59

There are many, many chips that you can utilize for this function. The simplest topology is probably inverting buck-boost, but there are others. Here is one of the cheapest and oldest chips (MC34063) in the inverting buck-boost configuration:

enter image description here

Obviously you would change R2/R1 ratio to get the correct -9V output voltage, as well as Rsc, L. The output capacitor could be reduced. You can go through the detailed design procedure in the datasheet. There are also some online calculators but I can't vouch for their accuracy.

Because the chip is old (low switching frequency) and your current low the inductor L will turn out to have a fairly high value, probably between 300uH and 1mH.

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