don steinbach, ae6pm1 battery voltage boost regulator solving the mary gomez park incident

Don Steinbach, AE6PM 1

Battery Voltage Boost Regulator

Solving the Mary Gomez Park Incident


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)


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)


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


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”


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/


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


The Finished Product


PCB Top

PC Board (Top)


PCB Bottom

PC Board (Bottom)

Note the 18 SMT capacitors installed


Transformer could be salvaged from a PC power

supply and rewound


N8XJK Schematic


Power Supply 101


Battery Boost Configuration


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.


N8XJK Schematic


Input fuse & filter

F1, F2, C1-C4

Switching transistors

Q1/Q3/Q6 and Q2/Q4/Q5

Transformer and rectifier

T1, D7

Low pass filter

L1, C5-C12

Pulse Width Modulator

(PWM)U1

Output voltage sensing

R3, R4, R5, R16Reference voltage divider

R1, R2, C15

Low battery protection

U2, Q7

RF detect

Q9, Q8, Q7 PWM IC compensation

C17

PWM operating frequency

C16, R6

RF Sample

13.8 Vdc9-12 Vdc

PWM Enable

2.5V

5.0V

N8XJK Block Diagram


N8XJK Schematic (simplified)

RF sense/PWM enable

Low battery protection/PWM disable


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)


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


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


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


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


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


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


The End

Mary Gomez Park Incident Solved

don steinbach, ae6pm1 battery voltage boost regulator solving the mary gomez park incident

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