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otuzsubat
Joined: 07 Jun 2004
Posts: 45
Helped: 2
Location: istanbul, Turkey
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 12 Jul 2004 10:33 DC-DC Converter Design with MAX618 |
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I need a up converter which has up to 28V input voltage and 12-20V adjustible output voltage. The properties of max618 Ok. But it has a max. 1W package. The typical aplication circuit is below. How can i improve output power of max618. I need your ideas. Thanks..
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batdin
Joined: 03 Jun 2004
Posts: 181
Helped: 3
Location: Bulgaria
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| 12 Jul 2004 14:28 Re: DC-DC Converter Design with MAX618 |
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My friend,
how can you expect to use a step-up converter for an input voltage greater than the output one?Not possible.
If the output voltage may be under and over the input voltage,you should use an inverting converter or a flyback with a transformer.
By the way,if the chip dissipates 1W,then the output power may be even 7-10W.
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otuzsubat
Joined: 07 Jun 2004
Posts: 45
Helped: 2
Location: istanbul, Turkey
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| 12 Jul 2004 20:38 DC-DC Converter Design with MAX618 |
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| Oh! i made a mistake. I have a 12 batteryand a solar panel which have max. 16V output voltage. When sun goes down the output voltage of panel decreases. I want to stabilize the output voltage about 20V and charge battery by this way. Normaly i use a relay in charging circuit. Instead of relay i want to use max618. But the package of max618 is too small. I don't think that it stands high charging current. I want to use max618 because the efficiency of charging circuit is very important for me.
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ME
Joined: 14 Mar 2002
Posts: 1770
Helped: 11
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| 12 Jul 2004 23:09 DC-DC Converter Design with MAX618 |
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For higher output power you should use a step-up controller with external MOSFET istead of a converter which have internal MOSFET.
The name "controller" is often used when it requires an extrnal MOSFET, while "converter" is used when it has integrated MOSFET (and sometimes diode too).
When you use an controller with external MOSFET all the power is dissapated in the MOSFET, so you should just select an MOSFET with low RDSon which can handle the power.
Try to look at MAX668 or similar controller instead:
Just use a schematic similar to Figure 4 of the daasheet.
MAX668, MAX669
1.8V to 28V Input, PWM Step-Up Controllers in µMAX
Flexible Converters Offer Step-Up, SEPIC, Flyback and Isolated Topologies. MAX668 Output Voltages Limited Only by External Component Ratings.
www.maxim-ic.com/quick_view2.cfm/qv_pk/1901
1.8V Minimum Start-Up Voltage (MAX669)
Wide Input Voltage Range (1.8V to 28V)
Tiny 10-Pin µMAX Package
Current-Mode PWM and Idle Mode™ Operation
Efficiency Over 90%
Adjustable 100kHz to 500kHz Oscillator or SYNC Input
220µA Quiescent Current
Logic-Level Shutdown
Soft-Start
Read this too, if you wan't to make the MAX668 even more efficient:
Simple Change Improves PFM Boost-Controller Efficiency
Modification to the standard PFM boost-controller circuit provides a 5% efficiency improvement at medium and light loads.
http://www.maxim-ic.com/appnotes.cfm/appnote_number/1054
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john_b
Joined: 11 May 2004
Posts: 22
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| 13 Jul 2004 17:41 Re: DC-DC Converter Design with MAX618 |
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| where ican find this ic
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ME
Joined: 14 Mar 2002
Posts: 1770
Helped: 11
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| 13 Jul 2004 17:45 Re: DC-DC Converter Design with MAX618 |
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| john_b wrote: |
| where ican find this ic |
You can order samples directly from Maxim's website.
It's free!!!
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otuzsubat
Joined: 07 Jun 2004
Posts: 45
Helped: 2
Location: istanbul, Turkey
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| 14 Jul 2004 15:30 DC-DC Converter Design with MAX618 |
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| thanks for your replies. i will try this ic's. maxim realy sends free samples. before i tried max618 and max 1771 by this way. you should fill a form to order free samples. you can find the form in maxim's site.
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ME
Joined: 14 Mar 2002
Posts: 1770
Helped: 11
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| 14 Jul 2004 15:48 DC-DC Converter Design with MAX618 |
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The suggested MOSFET FDS6680 can also be orederd as free sample from Fairchild and the suggested schottky diode MBRS340T3 can be ordered as free sample from ON Semiconductor.
Coils, capacitors and resistors can also be ordered as free samples from various vendors.
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