Path: utzoo!attcan!uunet!husc6!bloom-beacon!mgm.mit.edu!wolfgang From: wolfgang@mgm.mit.edu (Wolfgang Rupprecht) Newsgroups: sci.electronics Subject: Re: 7805 regulator Message-ID: <5770@bloom-beacon.MIT.EDU> Date: 14 Jun 88 21:16:26 GMT References: <592@picuxa.UUCP> Sender: daemon@bloom-beacon.MIT.EDU Reply-To: wolfgang@mgm.mit.edu.UUCP (Wolfgang Rupprecht) Organization: Freelance Software Consultant, Boston, Ma. Lines: 36 Summary: Expires: Sender: Followup-To: Distribution: Keywords: > I have a question about the MC7805 5V 1A regulator. Can you parallel > two of these devices together to derive a higher current? Parallelling them is not very clean. You have the problem that both regulators will have *slightly* different output voltages. The one with the higher voltage will try to carry the full load, up to the point where it goes into current limiting. At this point the voltage will drop till the second one picks up this excess load. The effective source impedance is quite high during this load pass-off. You can always try to use a simple PNP buffer as such: (Any high-current silicon PNP will do.) ~+8v in +5 out o---+----\ /-------------------+----o | \ / | | v / | | --------- +5v reg. | | | +--------+ | | 2.7 ohm| | | | +--\/\/\-+--------+ in out+------+ | | gnd | | | +---+----+ | --- 0.1 uf // | --- 0.1 uf // 10uf tantalum --- 10 uf tant V --- | | | | v v If you have problems with oscillations you can put a few 10's pf capacitance between the base and collector of the PNP. Invert this circuit for a negative supply booster. --- Wolfgang Rupprecht ARPA: wolfgang@mgm.mit.edu (IP 18.82.0.114) TEL: (617) 267-4365 UUCP: mit-eddie!mgm.mit.edu!wolfgang