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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 7 The Finished Product Don Steinbach, AE6PM 8 PCB Top PC Board (Top) Don Steinbach, AE6PM 9 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 12 Power Supply 101 Don Steinbach, AE6PM 13 Battery Boost Configuration Don Steinbach, AE6PM 14 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 15 N8XJK Schematic Don Steinbach, AE6PM 16 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 17 N8XJK Schematic (simplified) RF sense/PWM enable Low battery protection/PWM disable Don Steinbach, AE6PM 18 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 19 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 20 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 21 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 23 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 24 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 25 The End Mary Gomez Park Incident Solved Don Steinbach, AE6PM 26