Download Battery Voltage Boost Regulator

Battery Voltage Boost Regulator
Solving the Mary Gomez Park Incident
Don Steinbach, AE6PM
1
The Mary Gomez Park Incident
• Yaesu FT-840 transceiver received bad (terrible) signal quality
reports on CW after being operated on battery power for an
extended period of time.
• Believed to be a result of the dc input voltage being out-of-spec
low.
– Actual battery voltage was near 11V
– FT-840 Spec is 13.5V +/- 10% (12.15 to 14.85)
Don Steinbach, AE6PM
2
Specification Review
• Battery Specs (100% SOC Voltage)
– Deep Cycle (Johnson Controls)
• 2.11 V/cell or 12.66 V
– Sealed Lead-Acid (Power Sonic)
• 2.15 V/cell or 12.9 V
• Transceivers Specs
– Yaesu FT-840
• 13.5 V ± 10% (12.15 to 14.85 V)
– Yaesu FT-847
• 13.8 V ± 10% (12.42 to 15.18 V)
– Alinco DX-70TH, ICOM IC-706MKIIG, Kenwood TS-2000,
Yaesu FT-857
• 13.8 ± 15% (11.73 to 15.87 V)
Don Steinbach, AE6PM
3
Possible Solutions
• Add a second battery (or a cell) in series with the primary battery
– Raise primary battery dc voltage to 14 or 18 or 24 volts and
regulate down to 13V
• Use a modified/enhanced computer UPS
– Let the primary battery power the UPS and let the UPS
power the transceiver ac power supply
• Use a dc/dc converter and regulator
– Use a conventional dc/dc converter to provide 18V then
regulate down to 13V
• Use a boost supply in series with the battery
– Add a differential voltage to the primary battery voltage
Don Steinbach, AE6PM
4
QST to the Rescue
• QST Article
– A 12V dc Boost Regulator for Battery Operation
• Daniel R. Kemppainen, N8XJK
• November 2004, page 37
Quote from the article:
“A dc-dc boost switching converter is the answer to low voltage
battery problems for mobile, portable or emergency-power
operation”
Don Steinbach, AE6PM
5
Step 1 – Check the Current Status
• Contacted the author regarding availability of bare PC board
– Author responded that circuit had been redesigned and that
farcircuits had PC boards for sale
• www.farcircuits.net
– Author also stated that he has uploaded the new design to
the ARRL website
• www.arrl.org/files/qst-binaries/
Don Steinbach, AE6PM
6
Step 2 – Build It
• Procure the PC board and the components
– FAR Circuits
• PCB, E-core and bobbin, toroid core
– Digikey
• Filter capacitors, power MOSFETs, Schottkey dual diode
• Anything that needs to fit the PCB layout
– Anchor Electronics
• Miscellaneous ICs, semiconductors, resistors, capacitors
• Wind the transformer
• Wind the filter inductor
• Stuff and solder the PC board
• Cut, bend and drill some aluminum
• Final electrical/mechanical assembly and heat sinking
• Test
Don Steinbach, AE6PM
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The Finished Product
Don Steinbach, AE6PM
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PCB Top
PC Board (Top)
Don Steinbach, AE6PM
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PCB Bottom
PC Board (Bottom)
Don Steinbach, AE6PM
Note the 18 SMT capacitors
installed
10
Don Steinbach, AE6PM
Transformer could be
salvaged from a PC power
supply and rewound11
N8XJK Schematic
Don Steinbach, AE6PM
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Power Supply 101
Don Steinbach, AE6PM
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Battery Boost Configuration
Don Steinbach, AE6PM
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N8XJK Design Concept
• The circuit is best visualized starting with a full-wave power
supply using a transformer with a center tapped secondary.
• The center tap, rather than being grounded, is connected to the
high side of the battery so that the power supply adds to the
battery voltage.
• Feedback from the total output voltage back to the full-wave
power supply causes the power supply to modulate its output
voltage to keep the sum of the battery voltage plus the power
supply voltage constant.
• The power supply that supplies the additional voltage is a
switch-mode design that operates from the same battery that is
supplying the baseline power.
• The IC that drives the switch-mode power supply provides the
regulation by modulating the pulse width.
Don Steinbach, AE6PM
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N8XJK Schematic
Don Steinbach, AE6PM
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N8XJK Block Diagram
Input fuse & filter
9-12 Vdc
F1, F2, C1-C4
Low battery
protection
U2, Q7
Switching
transistors
Transformer
and rectifier
Q1/Q3/Q6 and
Q2/Q4/Q5
T1, D7
Pulse Width
Modulator
(PWM)
U1
Low pass filter
L1, C5-C12
13.8 Vdc
Output voltage
sensing
5.0V
Reference
voltage divider
R3, R4, R5, R16
2.5V
R1, R2, C15
RF
Sample
RF detect
Q9, Q8, Q7
PWM Enable
PWM IC
compensation
C17
PWM operating
frequency
C16, R6
Don Steinbach, AE6PM
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N8XJK Schematic (simplified)
RF sense/PWM enable
Low battery protection/PWM disable
Don Steinbach, AE6PM
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User Comments/Modification
• Battery protection circuit
– Reacts too quickly (false alarms)
– Can only be reset by removing input power
• RF detection/enable
– Boost power supply turned on only during transmit
• Different voltage during transmit and receive
• Not recommended IMHO
– Quiescent current is only 22 mA
I disabled battery protection & RF detection
by removing U2 and grounding emitter of
Q7 (jumper U2-1 to U2-12)
Don Steinbach, AE6PM
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Test Results
• Test Duration: 6 minutes, continuous
– Input Voltage: 12.16 V dc
– Output Voltage: 13.0 V dc
– Output Current: 16 A dc
• Maximum Temperatures (IR Thermometer):
– Transformer: 145 deg F
– Diode area: 180 deg F
– Heat sink area: Very hot to touch
– Filter capacitors: Slightly warm
• Switching Frequency: 40 kHz
• Ripple voltage: 17 mV p-p
Don Steinbach, AE6PM
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Test Results (Continued)
• Quiescent current (no load)
– Input = 12 Vdc, Output = 13.4 Vdc
– Input current = 21.8 mA
• Output voltage range adjustment (no load)
– Input = 12 Vdc
– Output voltage = 11.9 Vdc to 15.3 Vdc
• Minimum input voltage for 13.4V output (no load)
– 7.6 Vdc
Don Steinbach, AE6PM
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Parts Selection
• This power converter operates at about 40 kHz, not 120 Hz
– Conventional aluminum electrolytics are ineffective as filter
capacitors
• Use low impedance (ESR) capacitors as specified
– The traditional 2N3055 NPN silicon transistor cannot switch
fast enough
• Also power dissipation
• Use HEXFET Power MOSFET as specified
– The rectifier diodes need to be low forward voltage drop
(desired) and fast switching (required)
• Use Schottky rectifier as specified
– SMT capacitors added by the author (18 total) indicate
probable RFI issues fixed
Don Steinbach, AE6PM
22
Parts Selection (Continued)
• FAR Circuits has the double-sided PCB (for new design) for
$17.00
– Add $8.00 for the T1 E-core and the L1 toroid core
• Or scavenge the cores from a defunct PC power supply
• Order C1 thru C12 from DigiKey (don’t substitute)
• Order U1 from DigiKey (limited availability)
• Order Q5, Q6 and D7 from DigiKey (limited availability)
• Order C13 thru C15 from DigiKey (Panasonic parts)
• Order C17, C18, C21 from DigiKey (Kemet parts)
• Order R16 from DigiKey (fits the PCB)
• Remaining ICs, transistors, resistors and capacitors can be
purchased from Anchor Electronics in Santa Clara for less
than $9.00
• Total cost will be under $100.00 (I’ve spent $81.58)
• Jameco may also be a source
Don Steinbach, AE6PM
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Design Comments
• C1 thru C12 voltage ratings are marginal (16V in 13V circuit)
– Probably ok since problem was input voltage too low
– And the output voltage is regulated
• Input has capability for two fuses in parallel
– Added by author in response to user requests
– This can be risky since load sharing is not guaranteed
• Why use 2.5V reference for comparator input when 5V would
provide more sensitivity to output voltage variations?
– Apparently older versions of the LM3524 were not suited for
a reference input voltage as high as 5V
Don Steinbach, AE6PM
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MFJ-4416 Version
Commercial
version from MFJ
• Note adition of
series RC
“snubbers” and
crowbar circuit
• Redesigned LV
& RF detect
• Shipped with
battery protection
circuit disabled
• ~ $139.95
Don Steinbach, AE6PM
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The End
Mary Gomez Park Incident Solved
Don Steinbach, AE6PM
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