Due to the low efficiency, 7805 is not recommend to be used on high voltage system, which will require a huge heat sink, and there will be lots of energy wasted. The MC34063 is not perfect for compact design, its switch frequency is too low and it will require large size L and C component to achieve the performance. Not recommended. Check some new buck regulator with 150K above frequency from National Semi and linear. They are the leader on SMPS. Funny N. Au Group Electronics, New Bedford, MA, http://www.AuElectronics.com ----- Original Message ---- From: Vasile Surducan To: Microcontroller discussion list - Public. Sent: Wednesday, June 25, 2008 7:02:42 AM Subject: Re: [EE] Switch voltage Regulator - What chip to use? 7805 http://www.st.com/stonline/products/literature/ds/2143.pdf page34/56 fig27 max35V input On 6/25/08, Jinx wrote: > http://www.onsemi.com/pub_link/Collateral/AN920-D.PDF > > http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF > > MC34063 does it for me. For what you want just about any cheap > buck switcher would do. But you don't specify other conditions. > If you're not fussy about efficiency it's possible to drop (eg pre- > regulate with a zener or just brute force with a resistor) the i/p > voltage and use any oscillator, even a 555 or a PIC for example, > as a switcher > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist