Post by thread:[OT:] Why ate Ifrared LED receivers shown back to

part 1 636 bytes content-type:text/plain; (decoded quoted-printable) I have seen several infrared receiver circuits were the anode is connected to the negative rail and cathode connected towards the positive rail. What am I missing here? ************************************************* Roy Hopkins :-) Tauranga New Zealand ************************************************* --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.637 / Virus Database: 408 - Release Date: 20/03/2004 -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu part 2 15764 bytes content-type:application/octet-stream; (decode)

> I have seen several infrared receiver circuits were the anode is connected to the negative rail and cathode connected towards the positive rail. > What am I missing here? The transistor polarity is normal. The transistor functions as an emitter follower with a gain of (essentially) 1. This acts as a buffer for the photodiode so it "sees" a high impedance load. The output is lower impedance than the diode by itself (but not very low). The 47uF and 10k act as a filter to remove power supply noise. RM -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

> I have seen several infrared receiver circuits were the anode is > connected to the negative rail and cathode connected towards the > positive rail. > > What am I missing here? Because that's how photodiodes work. Reverse leakage current increases with indcident light. -- Brent Brown, Electronic Design Solutions 16 English Street, Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/txt: 025 334 069 eMail: brent.brownKILLspamclear.net.nz -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

{Quote hidden}>-----Original Message----- >From: Russell McMahon [EraseMEapptechspam_OUTTakeThisOuTPARADISE.NET.NZ] >Sent: 31 March 2004 06:47 >To: PICLISTspam_OUTMITVMA.MIT.EDU >Subject: Re: [OT:] Why ate Ifrared LED receivers shown back to front? > > >> I have seen several infrared receiver circuits were the anode is >> connected >to the negative rail and cathode connected towards the positive rail. > >> What am I missing here? > >The transistor polarity is normal. > >The transistor functions as an emitter follower with a gain of >(essentially) 1. This acts as a buffer for the photodiode so >it "sees" a high impedance load. The output is lower impedance >than the diode by itself (but not very low). > >The 47uF and 10k act as a filter to remove power supply noise. Right answer to the wrong post Russell? ;') A photo-diode can be operated in one of two ways. It can be used as a small "solar cell", i.e. it will generate a small current when exposed to light. If used in this manner, the device would be forwards biased. The other property of photodiodes is that the "leakage" current when reversed biased is proportional to the intensity of the light it is exposed to. This is how the device is used in the circuits you have seen. This method has the advantage of moving carriers from the depletion region out very quickly, and gives the device a much faster response than using it forwards biased. Typicaly you can get PIN based photodiodes that can operate with a bandwidth of 7GHz or even higher for high speed data over optical fibres. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to @spam@postmasterKILLspambookham.com. -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

STOP THE PRESS - thanks guys did not know that - WOW have learnt something. > A photo-diode can be operated in one of two ways. It can be used as a small > "solar cell", i.e. it will generate a small current when exposed to light. > If used in this manner, the device would be forwards biased. > > The other property of photodiodes is that the "leakage" current when > reversed biased is proportional to the intensity of the light it is exposed > to. This is how the device is used in the circuits you have seen. This > method has the advantage of moving carriers from the depletion region out > very quickly, and gives the device a much faster response than using it > forwards biased. > > Typicaly you can get PIN based photodiodes that can operate with a bandwidth > of 7GHz or even higher for high speed data over optical fibres. > > Regards > > Mike --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.637 / Virus Database: 408 - Release Date: 20/03/2004 -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu