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Old 9th December 2003, 03:57 PM   #1
Alcaid is offline Alcaid  Norway
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Default Low Power Negative Car Power Supply

Anyone tried out Rod Elliot's circuit to produce a negative supply in the car to power an active filter?

http://www.sound.westhost.com/project95.htm

Have anyone got any other circuits, or improvements to Rod's?
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Old 10th December 2003, 01:41 AM   #2
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Default negative output smps recommendation

I would enthusiastically recommend an inverting buck-boost converter using the UC3572 PWM control IC. It is very desirable to have regulated dc voltages. Otherwise the output voltage changes with changes in input voltage. This occurs when the engine speed changes, and at lower temperatures, diodes have a larger forward drop for a given forward current. I've used and still use charge pump based converters similar to the RE design you provided the link for. They are good if the output voltage does not need to be tightly regulated. The TI web site has app notes for buck boost converters, and the data sheet for the UC3572. I'm using it in a current product design that has a -4 volt, -0.42 amp SMPS, switching at 225 kHz. The output is quiet, without a post LC filter. The only caveat is that the controller needs external frequency compensation to assure stability. The app notes cover this. If you'd rather avoid doing this, the On Semiconductor MC34063A makes a good negative converter, and is internaly compensated. You must, however, use an aluminum or tantalum electrolytic output filter cap, for stability. The On Semi site has the MC34063A data sheet. Also, the app notes AN-920, and AN-954 detail the use of the chip, and explain the inverting buck-boost circuit in detail. I've attached them for convenience, as well as the UC3572. The computations are very straightforward, and I've coached designers unfamiliar with SMPS and they seemed to have little trouble using the MC334063A. It is dated, but if ultra small size, and speed isn't needed, it should work fine. I hope this helps.
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File Type: zip negative_smps.zip (20.0 KB, 67 views)
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Old 10th December 2003, 01:44 AM   #3
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Default negative output smps recommendation

I would enthusiastically recommend an inverting buck-boost converter using the UC3572 PWM control IC. It is very desirable to have regulated dc voltages. Otherwise the output voltage changes with changes in input voltage. This occurs when the engine speed changes, and at lower temperatures, diodes have a larger forward drop for a given forward current. I've used and still use charge pump based converters similar to the RE design you provided the link for. They are good if the output voltage does not need to be tightly regulated. The TI web site has app notes for buck boost converters, and the data sheet for the UC3572. I'm using it in a current product design that has a -4 volt, -0.42 amp SMPS, switching at 225 kHz. The output is quiet, without a post LC filter. The only caveat is that the controller needs external frequency compensation to assure stability. The app notes cover this. If you'd rather avoid doing this, the On Semiconductor MC34063A makes a good negative converter, and is internaly compensated. You must, however, use an aluminum or tantalum electrolytic output filter cap, for stability. The On Semi site has the MC34063A data sheet. Also, the app notes AN-920, and AN-954 detail the use of the chip, and explain the inverting buck-boost circuit in detail. The computations are very straightforward, and I've coached designers unfamiliar with SMPS and they seemed to have little trouble using the MC334063A. It is dated, but if ultra small size, and speed isn't needed, it should work fine. I hope this helps.
Attached Files
File Type: zip negative_smps.zip (40.0 KB, 38 views)
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Old 11th December 2003, 03:32 PM   #4
Alcaid is offline Alcaid  Norway
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Sounds to hard to make for me.

Anyone tried out MAXIMs MAX742 Switch-Mode Regulator with 5V to 12 or 15V Dual-Output?

Then all i would need to do is to regulate the 12-13.8V from the battery down to 5V, and build the circuit in the data sheet.

Would the switch mode make my crossover noisy?
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