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#1
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Photodiode Question
What current would one expect to see from a photodiode exposed to
typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#2
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
Jim Thompson wrote:
What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. Lots -- I did something like this a few years ago and saw several milliamps. But as you really should know, the real answer is "it depends". It depends on the diode area, whether it's shaded, what the customer thinks "bright" is, ect. Order a few from Digikey, cobble up something with a 9V battery and an ammeter, and go measure it! Then use the sensitivity on that data sheet to extrapolate to what you'd expect from other similar diodes. One thing that you will learn is that your eyeballs have an amazing capability to accommodate changes in lighting, and that "bright" for a room doesn't hold a candle to "bright" for a sunny day. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com |
#3
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
Jim Thompson wrote:
What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson As Tim said, "It depends". Tim mentioned the "obvious suspects" - how big is the photodiode? (1 mm x 1 mm or 1 cm x 1 cm - it will make a difference...), how bright is "bright"? (IIRC, the eye's photoresponse is logarithmic, but a photodiode is linear over several orders of magnitude in illumination), etc. One thing Tim didn't mention is the frequency response of the photodiode. Do you and your client only care about DC illumination, or does the photodiode have to be able to deal with the illumination switching on and off at several tens or a few hundred kHz. In general, if only DC is of concern, the photodiode can be designed to have better responsivity - the current out per unit optical power in. Also, with the photodiode be reverse-biased or zero-biased? (Reverse bias will improve the responsivity) but not applying an external bias voltage across the PD will make things simpler. Depending on what the client's needs are, you might want to consider using a photoconductor instead of a photodiode. Bob Pownall |
#4
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. Photodiode could be not a very good idea, as they depend on everything. A good part for luminance detection is TPS851 from Toshiba. See the datasheet for details. If you want to isolate the light sensor from being illuminated by your own backlight, you can time multiplex the backlight and the sensor. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com |
#5
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
Jim Thompson wrote:
What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson For simple detection of ambient light level with no requirement of high linearity, I find LDRs more sensitive and easier to work with. They correspond fairly well with human spectral response too. |
#6
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On 3/21/2010 11:10 PM, Jim Thompson wrote:
What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson Those guys are all nuts. For backlight control, you can use one of the ambient light sensors such as the Intersil ISL29000 or TAOS TSL2560, for instance. They look after all of that nonsense, and produce an analogue or digital output proportional to just the perceived brightness (i.e. luminous intensity), without being fooled by all the IR from incandescents, for instance. Full zenith sunlight is about 800W/m**2, so figuring 0.3 A/W average responsivity, a typical 2.3 mm square photodiode such as a BPW34 will never produce more than ~1.3 mA without optical concentration of some sort. Indoors it's a factor of 10**3 to 10**4 dimmer than that, so you're looking at a few microamps in bright room lights. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net |
#7
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs
wrote: On 3/21/2010 11:10 PM, Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson Those guys are all nuts. Then I'm sure glad I didn't make any suggestions. John |
#8
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On 3/22/2010 9:52 AM, John Larkin wrote:
On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs wrote: On 3/21/2010 11:10 PM, Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson Those guys are all nuts. Then I'm sure glad I didn't make any suggestions. John Nah, it's just my rhetorical way of trying to get people to do a bit of calculation (or even experiment) before giving advice. I know, I know, I'm on Usenet, but we must live in hope. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net |
#9
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On Mon, 22 Mar 2010 11:51:00 +0530, "pimpom"
wrote: Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson For simple detection of ambient light level with no requirement of high linearity, I find LDRs more sensitive and easier to work with. They correspond fairly well with human spectral response too. That could be made to work as well. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy |
#10
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs
wrote: On 3/21/2010 11:10 PM, Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson Those guys are all nuts. For backlight control, you can use one of the ambient light sensors such as the Intersil ISL29000 or TAOS TSL2560, for instance. They look after all of that nonsense, and produce an analogue or digital output proportional to just the perceived brightness (i.e. luminous intensity), without being fooled by all the IR from incandescents, for instance. Full zenith sunlight is about 800W/m**2, so figuring 0.3 A/W average responsivity, a typical 2.3 mm square photodiode such as a BPW34 will never produce more than ~1.3 mA without optical concentration of some sort. Indoors it's a factor of 10**3 to 10**4 dimmer than that, so you're looking at a few microamps in bright room lights. Cheers Phil Hobbs My task is to produce a PWM output proportional to a photodiode current. I guess I need to find a typical one and measure it myself. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy |
#11
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
"Jim Thompson" wrote in
message ... My task is to produce a PWM output proportional to a photodiode current. I guess I need to find a typical one and measure it myself. Well, you didn't specify what kind of proportionality, so I guess I win firsties. http://webpages.charter.net/dawill/I...odiode_PWM.gif Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
#12
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
"Tim Williams" wrote in message ... http://webpages.charter.net/dawill/I...odiode_PWM.gif Tim Geez, I haven't futzed with PUTs in ages. Does anybody still make them? |
#13
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On Mon, 22 Mar 2010 10:07:56 -0500, "Tim Williams"
wrote: "Jim Thompson" wrote in message ... My task is to produce a PWM output proportional to a photodiode current. I guess I need to find a typical one and measure it myself. Well, you didn't specify what kind of proportionality, so I guess I win firsties. http://webpages.charter.net/dawill/I...odiode_PWM.gif Tim .... for certain definitions of "PWM." But yeah, PUTs were fun. John |
#14
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
"Oppie" wrote in message
... http://webpages.charter.net/dawill/I...odiode_PWM.gif Geez, I haven't futzed with PUTs in ages. Does anybody still make them? PUTs aren't that hard to find. Maybe you're thinking of UJTs? http://www.mouser.com/ProductDetail/...URy1Y7q4hnw%3d Although I'll admit none of them are actually *in stock* right now. Anyway, if they're on the expensive side ($0.25 in singles?), you can Jeorgify your own from a 2N3904 and 2N3906 ($0.06/ea in singles)... the equivalent circuit is as indicated (i.e., like an SCR, but take the second junction). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
#15
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On Mon, 22 Mar 2010 10:07:56 -0500, "Tim Williams"
wrote: "Jim Thompson" wrote in message ... My task is to produce a PWM output proportional to a photodiode current. I guess I need to find a typical one and measure it myself. Well, you didn't specify what kind of proportionality, so I guess I win firsties. http://webpages.charter.net/dawill/I...odiode_PWM.gif Tim Except that's current-to-frequency :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy |
#16
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
"Jim Thompson" wrote in
message ... http://webpages.charter.net/dawill/I...odiode_PWM.gif Except that's current-to-frequency :-) On-time is constant, so it's PWM. You didn't say if frequency had to be constant. No specs, remember? ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
#17
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On Mon, 22 Mar 2010 09:58:43 -0400, Phil Hobbs
wrote: On 3/22/2010 9:52 AM, John Larkin wrote: On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs wrote: On 3/21/2010 11:10 PM, Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson Those guys are all nuts. Then I'm sure glad I didn't make any suggestions. John Nah, it's just my rhetorical way of trying to get people to do a bit of calculation (or even experiment) before giving advice. I know, I know, I'm on Usenet, but we must live in hope. Cheers Phil Hobbs I recall a recent lawsuit (maybe the Hynix/TI thing) over a design for an ambient light sensor chip that used semi processing to get human-similar wavelength response. Scads of people offer ambient light sensor chips. John |
#18
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
John Larkin wrote:
On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs wrote: On 3/21/2010 11:10 PM, Jim Thompson wrote: What current would one expect to see from a photodiode exposed to typical bright room light (used to control a backlight proportional to room light)? As usual, my customer has no clue. My only concern, design wise, is to build a micropower transconductance amplifier with sufficient output drive to handle the maximum available photo current. ...Jim Thompson Those guys are all nuts. Then I'm sure glad I didn't make any suggestions. John I couldn't agree any more. Your decision is well understood! |
#19
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
On 2010-03-22, Jim Thompson wrote:
On Mon, 22 Mar 2010 10:07:56 -0500, "Tim Williams" wrote: "Jim Thompson" wrote in message ... My task is to produce a PWM output proportional to a photodiode current. I guess I need to find a typical one and measure it myself. Well, you didn't specify what kind of proportionality, so I guess I win firsties. http://webpages.charter.net/dawill/I...odiode_PWM.gif Tim Except that's current-to-frequency :-) It doesn't have to be, feed a square wave clock through a small capacitor to the gate if there's a particular frequency you want. --- news://freenews.netfront.net/ - complaints: --- |
#20
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad
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Photodiode Question
"Tim Williams" wrote in message
... "Oppie" wrote in message ... http://webpages.charter.net/dawill/I...odiode_PWM.gif Geez, I haven't futzed with PUTs in ages. Does anybody still make them? PUTs aren't that hard to find. Maybe you're thinking of UJTs? http://www.mouser.com/ProductDetail/...URy1Y7q4hnw%3d Although I'll admit none of them are actually *in stock* right now. Anyway, if they're on the expensive side ($0.25 in singles?), you can Jeorgify your own from a 2N3904 and 2N3906 ($0.06/ea in singles)... the equivalent circuit is as indicated (i.e., like an SCR, but take the second junction). Tim Last time I worked with them was about 25 years ago. It was used as a oscillator/ramp generator for a proportional heating control system in a 'Centrifichem' blood chemistry analyzer. Oppie |
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