The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> inverting Boost converter
https://designers-guide.org/forum/YaBB.pl?num=1397725399

Message started by bki on Apr 17^th, 2014, 2:03am

Title: inverting Boost converter
Post by bki on Apr 17^th, 2014, 2:03am

Hi,

i am circuit design beginner (student) and have a little problem.
I need to design an integrated inverting boost converter that is able to generate -70V (negative voltage) at the output from 5V input supply.

The technology that i use only allows me to use NMOS transistors and the source of those transistors need to be connected to ground.
Therefore, i can not use a regular inverting Boost Converter topology, where the switch connects the input voltage to the inductor node.

Any ideas how to implement the circuit instead?

Title: Re: inverting Boost converter
Post by loose-electron on Apr 22^nd, 2014, 3:39pm

Are you inside an IC or on a PCB?

You can generate the V+ (say 80V with a LC boost circuit) and then use sequenced switches to take that voltage and invert it to -80V

Charge the capacitor to 80V, and then sequence switches on a holding capacitor to make it -80V, where you use a diode (needs to float from substrate) to dump it into a holding capacitor.

Title: Re: inverting Boost converter
Post by bki on Apr 23^rd, 2014, 4:53am

Hi,

thanks for your message. It is for an IC.

I am not a native english speaker, therefore i don´t really understand what do you mean with sequence switches ?
Maybe do you have a picture example?

Thank a lot for your help!

Title: Re: inverting Boost converter
Post by loose-electron on Apr 23^rd, 2014, 3:00pm

http://www.linear.com/products/Inverting_Regulators

Take a look at the above devices, this is what you are trying to do.

Title: Re: inverting Boost converter
Post by bki on Apr 24^th, 2014, 5:39am

exactly, but i am doing it integrated. So, i can not use another IC.
My big problem is that my technology offers no PMOS transistors - only NMOS.

Title: Re: inverting Boost converter
Post by loose-electron on Apr 24^th, 2014, 4:25pm

you may have to create what are called "boot power" to bias the NMOS transistors above the power supply rail to use NMOS switches only.

see:

http://4.bp.blogspot.com/-GZBCM0xlSbk/UPvnSo5w4rI/AAAAAAAAAZo/YUTt0KpFnPA/s1600/IR2110+block.png

which shows an example of how to control an NMOS transistor to switch a large positive voltage.