PSU Recruitment Through GATE- Preparation Guidelines and PSU Details
Designing a better Amiga PSU - forum.icomp.de
Transcript of Designing a better Amiga PSU - forum.icomp.de
Designing a better Amiga PSU
Jens Schönfeld, CEO/owner of individual Computers GmbH www.icomp.de
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Overview
● Existing solutions● Original Commodore spec● Load performance, observations● Strategies against voltage drop● Milestone: New specification● Basic principle of DC-DC conversion● Compensation circuit & performance
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Existing solutions
● Commodore transformer-based PSU● Commodore switch mode PSU● Meanwell-based second-source● Cisco-based second-source● Modified ATX PSU
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Original Commodore specification
● http://www.kaiiv.de/servicemanuals/A500_Power_Supply_Specification.pdf
● Very strict specification:
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How to apply load
„electronic load“ is problematic, as it may cause oscillation
=> classic load with resistors
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Measurement setup
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Ripple measurement (from spec)
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Voltage dependency on current
1,8 2,26 2,7 3,13 3,56 3,98 4,38 4,76 5,154
4,2
4,4
4,6
4,8
5
5,2
5,4
A600-3A A500-2.5A A1200-3A
A500-4.3A MeanWell 4A Cisco
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Ripple voltage
1,8 2,26 2,7 3,13 3,56 3,98 4,38 4,76 5,150
20
40
60
80
100
120
A600-3A A500-2.5A A1200-3A
A500-4.3A MeanWell 4A Cisco
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Observations
● Voltage drops linear with current● Ripple is out of spec on almost all
PSUs in the series of measurement● Overload behaviour of Cisco PSU is
potentially dangerous („hickup mode“)● 5V rail changes with load on 12V
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Explanations of observations
● Voltage drop is caused by Ohm‘s law● Ripple is out of spec on old PSUs
because capacitors probably dry● Cisco PSU is just built like that – and
therefore not suitable for an expanded Amiga.
● 12V return current flows through the same wire as 5V return current
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Strategies against voltage drop
● Thicker wires, shorter cables● Using the shield line as additional
GND: bad idea!● Sense wire in the cable: Will not sense
voltage drop in line filter● Current-dependent voltage adaption:
Method of choice!
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New specification
● For use on A500, A600 and A1200● Should handle lots of expansions● Shall never drop below 5V for overclocking
success● Fanless: low-noise, low-temp● Shall keep 5V stable with varying 12V load● the switch shall be close to the computer● Legal constraints must be handled by a
small company like iComp :-)
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Legal constraints
● Mains-connected devices have to go through a number of safety tests
● Cost of such tests are around 40.000,- EUR for global market compliance
==> the mains-connected part must be an off-the-shelve part.
● Malfunction might cause severe damage: We need insurance!
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DC-DC converter modding
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Current sensing circuit
Picture source:Stackexchange.com
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First prototype performance
1,8 2,26 2,7 3,13 3,56 3,984,65
4,7
4,75
4,8
4,85
4,9
4,95
5
5,05
iComp Proto#1
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Second prototype performance
1,8 2,26 2,7 3,13 3,56 3,98 4,38 4,76 5,154,65
4,7
4,75
4,8
4,85
4,9
4,95
5
5,05
5,1
iComp Proto#1 iComp Proto#2
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Are we there yet?
● The power LED on the converter changes it‘s brightness depending on load
● Solution: Another regulation circuit!
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Final comparison
1,8 2,26 2,7 3,13 3,56 3,98 4,38 4,76 5,154
4,2
4,4
4,6
4,8
5
5,2
5,4
A600-3AA500-2.5AA1200-3AA500-4.3AMeanWell 4ACiscoiComp Proto#1iComp Proto#2
1,8 2,26 2,7 3,13 3,56 3,98 4,38 4,76 5,150
20
40
60
80
100
120
140
A600-3A A500-2.5A
A1200-3A A500-4.3A
MeanWell 4A Cisco
iComp Proto#1 iComp Proto#2
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Thank you!
● Revision team● OBS studio team● The Libre office foundation● The Amiga community● The team at iComp GmbH