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HV Bias Supply Challenge
OK, here's a challenge to you guys ... I have been trying to ID a IC /
inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Thanks Tony, KD7TOG ( KD7TOG at earthlink dot net ) |
KD7TOG wrote:
OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Nothing is likely to be very efficient at this low power level. I think I would look into a step up transformer design, perhaps using something like a MT4143: http://www.tamuracorp.com/pdf/MET-01.pdf driven by a two transistor half bridge at ultrasonic frequency. With a 14 to 1 step up, it could produce 200 volts peak across the whole secondary, with only 7 volts peak across half its primary. If the secondary was connected to a voltage doubler, you could drive it with half that. The transformer is rated for 10 mw, but at 20 kHz, I think it could do a bit more than that or run fairly efficiently at much less. -- John Popelish |
KD7TOG wrote:
OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Nothing is likely to be very efficient at this low power level. I think I would look into a step up transformer design, perhaps using something like a MT4143: http://www.tamuracorp.com/pdf/MET-01.pdf driven by a two transistor half bridge at ultrasonic frequency. With a 14 to 1 step up, it could produce 200 volts peak across the whole secondary, with only 7 volts peak across half its primary. If the secondary was connected to a voltage doubler, you could drive it with half that. The transformer is rated for 10 mw, but at 20 kHz, I think it could do a bit more than that or run fairly efficiently at much less. -- John Popelish |
Tony,
To make it easy snag one of the surplus electronic flash units or dismantle a disposable camera. Some of them are quite small. An RC filter will clean up the DC and a simple resistor voltage divider to cut the voltage to what you want. Regulation shouldn't be a problem with a steady and low current draw. To get the input current down it may help to swap the photoiflash capacitor for something with very low leakage. 73, Jim On Wed, 10 Dec 2003 00:28:50 GMT, "KD7TOG" wrote: OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Thanks Tony, KD7TOG ( KD7TOG at earthlink dot net ) |
Tony,
To make it easy snag one of the surplus electronic flash units or dismantle a disposable camera. Some of them are quite small. An RC filter will clean up the DC and a simple resistor voltage divider to cut the voltage to what you want. Regulation shouldn't be a problem with a steady and low current draw. To get the input current down it may help to swap the photoiflash capacitor for something with very low leakage. 73, Jim On Wed, 10 Dec 2003 00:28:50 GMT, "KD7TOG" wrote: OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Thanks Tony, KD7TOG ( KD7TOG at earthlink dot net ) |
In article . net, "KD7TOG"
writes: OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. A simple low-RF oscillator can do it with a small transformer having an enormous turns ratio. I'd suggest a toroidal type with a ferrite core rather than powdered-iron core to work around 50 to 100 KHz. Something like a 1:30 turns ratio seems about right with the secondary tuned, the primary driven by a single transistor emitter, feedback to the base which will also load down the tuned secondary some. Maybe a Darlington connection using two bipolars if too much resistive loading. Since a 2.5 mHy 4-pie RFC and 1000 pFd tune very close to 100 KHz, you might use that as the "secondary." The "primary" could have several turns wound in between the pie sections. Bulkier than a toroid but a lot easier to handle on the first go-around for feasibility checking. With 3900 pFd, the 2.5 mHy RFC will tune about 51 KHz. Staying in the LF region allows most ordinary newer silicon diodes to directly rectify the LF yet the harmonics don't interfere much with AM radios nearby. It's well above the top frequency for human hearing so a simple C-R-C filter ought to make the DC fairly clean for the microphone without too much C value and bulk. Len Anderson retired (from regular hours) electronic engineer person |
In article . net, "KD7TOG"
writes: OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. A simple low-RF oscillator can do it with a small transformer having an enormous turns ratio. I'd suggest a toroidal type with a ferrite core rather than powdered-iron core to work around 50 to 100 KHz. Something like a 1:30 turns ratio seems about right with the secondary tuned, the primary driven by a single transistor emitter, feedback to the base which will also load down the tuned secondary some. Maybe a Darlington connection using two bipolars if too much resistive loading. Since a 2.5 mHy 4-pie RFC and 1000 pFd tune very close to 100 KHz, you might use that as the "secondary." The "primary" could have several turns wound in between the pie sections. Bulkier than a toroid but a lot easier to handle on the first go-around for feasibility checking. With 3900 pFd, the 2.5 mHy RFC will tune about 51 KHz. Staying in the LF region allows most ordinary newer silicon diodes to directly rectify the LF yet the harmonics don't interfere much with AM radios nearby. It's well above the top frequency for human hearing so a simple C-R-C filter ought to make the DC fairly clean for the microphone without too much C value and bulk. Len Anderson retired (from regular hours) electronic engineer person |
The guy with the flash camera idea is on track. Audio Express Magazine had
a writeup on them a few months ago, as did Nuts and Volts some years back. I reverse engr'd a Fuji camera and it's just like the AE Mag circuit. Circa 1976, I made a simple two transistor oscillator, which ran off a 1.5 volt battery that connected across a reversed filament transformer, lite a neon bulb for weeks. I'm sure it would really honk with 9 volts DC chop input. cheers skipp http://sonic.ucdavis.edu : KD7TOG wrote: : OK, here's a challenge to you guys ... I have been trying to ID a IC / : inductor combination to generate 150 to 200 VDC ... in the nano-microamp : range. I need to supply a bias voltage to an electrostatic microphone : element. : Any ideas ?? : Wish list: : Very low current ... 2ma ;-) : Runs from 5 to 9 volt DC source : Minimal components : Most of the specs I find for HV units ( backlight supplies ) are too much : current. Most of the inductor type DC-DC converters seem geared towards low : voltage high current apps. : Will watch the discussion for tips and ideas ... all welcome. : Thanks : Tony, KD7TOG : ( KD7TOG at earthlink dot net ) |
The guy with the flash camera idea is on track. Audio Express Magazine had
a writeup on them a few months ago, as did Nuts and Volts some years back. I reverse engr'd a Fuji camera and it's just like the AE Mag circuit. Circa 1976, I made a simple two transistor oscillator, which ran off a 1.5 volt battery that connected across a reversed filament transformer, lite a neon bulb for weeks. I'm sure it would really honk with 9 volts DC chop input. cheers skipp http://sonic.ucdavis.edu : KD7TOG wrote: : OK, here's a challenge to you guys ... I have been trying to ID a IC / : inductor combination to generate 150 to 200 VDC ... in the nano-microamp : range. I need to supply a bias voltage to an electrostatic microphone : element. : Any ideas ?? : Wish list: : Very low current ... 2ma ;-) : Runs from 5 to 9 volt DC source : Minimal components : Most of the specs I find for HV units ( backlight supplies ) are too much : current. Most of the inductor type DC-DC converters seem geared towards low : voltage high current apps. : Will watch the discussion for tips and ideas ... all welcome. : Thanks : Tony, KD7TOG : ( KD7TOG at earthlink dot net ) |
Thanks all for the ideas ... I have a couple of potential solutions.
Tony, KD7TOG |
Thanks all for the ideas ... I have a couple of potential solutions.
Tony, KD7TOG |
One more idea -- the old mass-produced geiger counters now available
cheaply on eBay have very simple HV supply circuits that use minimal components, and run from 1.5 to 6 or so volts, depending on the model. They come with a schematic and parts list. Although the parts are just about all obsolete, you could find modern substitutes that would work. Roy Lewallen, W7EL KD7TOG wrote: Thanks all for the ideas ... I have a couple of potential solutions. Tony, KD7TOG |
One more idea -- the old mass-produced geiger counters now available
cheaply on eBay have very simple HV supply circuits that use minimal components, and run from 1.5 to 6 or so volts, depending on the model. They come with a schematic and parts list. Although the parts are just about all obsolete, you could find modern substitutes that would work. Roy Lewallen, W7EL KD7TOG wrote: Thanks all for the ideas ... I have a couple of potential solutions. Tony, KD7TOG |
Photoflash units typically keep oscillating and drawing power even
when the cap is charged, but if you arrange to turn one really OFF most of the time, the average current could be very low. You just need a cap that will hold the charge well. Polypropylenes are known to do a very good job in that respect, but in any event the reverse leakage of the rectifier diode is likely to dominate. It's possible to come up with ridiculously low reverse leakage rectifiers if it's an issue. Because of the low current required, it's worth thinking about using a voltage multiplier. A simple blocking oscillator (transformer and transistor) with even just 5:1 stepup to the secondary, then some voltage multiplication, should do it. You didn't mention regulation: the mic sensitivity will generally be proportional to the bias voltage, so some regulation is probably appropriate. Another possibility: a stack of 60 or so lithium coin cells. Quiet, good voltage stability, ten year life. At about 40 cents each from DigiKey, the $25 cost is probably less than you do an 'lectronic solution if your time is worth anything. Can be packaged into a cylinder about an inch in diameter and four inches long. (PVC pipe + fittings + small spring?) Completely isolated: no possible ground loops. No oscillator to generate noise. Cheers, Tom "KD7TOG" wrote in message link.net... OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Thanks Tony, KD7TOG ( KD7TOG at earthlink dot net ) |
Photoflash units typically keep oscillating and drawing power even
when the cap is charged, but if you arrange to turn one really OFF most of the time, the average current could be very low. You just need a cap that will hold the charge well. Polypropylenes are known to do a very good job in that respect, but in any event the reverse leakage of the rectifier diode is likely to dominate. It's possible to come up with ridiculously low reverse leakage rectifiers if it's an issue. Because of the low current required, it's worth thinking about using a voltage multiplier. A simple blocking oscillator (transformer and transistor) with even just 5:1 stepup to the secondary, then some voltage multiplication, should do it. You didn't mention regulation: the mic sensitivity will generally be proportional to the bias voltage, so some regulation is probably appropriate. Another possibility: a stack of 60 or so lithium coin cells. Quiet, good voltage stability, ten year life. At about 40 cents each from DigiKey, the $25 cost is probably less than you do an 'lectronic solution if your time is worth anything. Can be packaged into a cylinder about an inch in diameter and four inches long. (PVC pipe + fittings + small spring?) Completely isolated: no possible ground loops. No oscillator to generate noise. Cheers, Tom "KD7TOG" wrote in message link.net... OK, here's a challenge to you guys ... I have been trying to ID a IC / inductor combination to generate 150 to 200 VDC ... in the nano-microamp range. I need to supply a bias voltage to an electrostatic microphone element. Any ideas ?? Wish list: Very low current ... 2ma ;-) Runs from 5 to 9 volt DC source Minimal components Most of the specs I find for HV units ( backlight supplies ) are too much current. Most of the inductor type DC-DC converters seem geared towards low voltage high current apps. Will watch the discussion for tips and ideas ... all welcome. Thanks Tony, KD7TOG ( KD7TOG at earthlink dot net ) |
In article et, "KD7TOG"
writes: Thanks all for the ideas ... I have a couple of potential solutions. Tony, KD7TOG This isn't a direct solution but it looked interesting if someone wants to try it - Harry Lythall's accidental discovery of an LM317 series voltage regulator as an RF oscillator at low HF. http://w1.859.telia.com/~u85920178/tx/317-tx.htm Use a toroidal core and/or a multiplying rectifier and the voltage could be sizeable. Len Anderson retired (from regular hours) electronic engineer person |
In article et, "KD7TOG"
writes: Thanks all for the ideas ... I have a couple of potential solutions. Tony, KD7TOG This isn't a direct solution but it looked interesting if someone wants to try it - Harry Lythall's accidental discovery of an LM317 series voltage regulator as an RF oscillator at low HF. http://w1.859.telia.com/~u85920178/tx/317-tx.htm Use a toroidal core and/or a multiplying rectifier and the voltage could be sizeable. Len Anderson retired (from regular hours) electronic engineer person |
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