Invertering DC/DC

You might want to consider TPS54260.  It looks like it will just make 1 A from 24 to -20 V.

Power dissipation may be a concern operating near the limit with the TPS54260 in an inverting topology. You may also want to consider the TPS54360 for better thermal performance.

Regards,
Anthony

I have tried to do a conversion from +24 V to-20V. It does not work. It is no switching. Current flows through the coil to ground. 

7080.Power -20V.pdf

best regards

Stefan

You may need to add 10 uF ceramic capacitor from VIN to the minus rail (IC GND). locate it as close to VIN pin as possible.

Hi John, thanks for yor answer.

I have added an extra 10µF capacitor and replaced the IC but it still do not work. Now I get +0.44V out?

Is there some heplful program for calculating the values of the comopnents?

best regards

Stefan

Hi Stefan,

You can use the excel spreadsheet in the following link as a tool to help calculate the component values. http://www.ti.com/litv/zip/slvc211c

EDIT: Also to reiterate John's comment. A ceramic capacitor from VIN to the GND pin of the IC is required for proper operation. This should be placed as close as possible to the VIN pin with the shortest return path possible to the GND pin.

Best Regards,
Anthony

Hi Anthony

thank´s for the spreadsheet. I have changed values of the components, but it is still same bad result Vout is +0.44V

I know I have to improve the layout in next revision but it is strange that I don´t get any - voltage?

best regards

Stefan

Hi Stefen,

What are the final components you ended up using? Do you have a part number for the output capacitor you selected?

After a closer look at the component selection, your diode might not be properly rated for this application. The switching node (PH) will swing from 24V to -20V, this means your diode needs a voltage rating of at least 44V. The 15MQ040 selected is only 40V.

Best Regards,
Anthony

Hi Anthony

Here are the final schematic.

8802.Power -20V.pdf

best regards

Stefan