HP Calculator Power Supplies from HP-35 to HP Prime Presented by: Jim Johnson HP Handheld Conference 2016 – Fort Collins, CO September 17-18, 2016

Synopsis: The challenges of providing power to a handheld device stretches the designers imagination and creativity. First you must provide enough power to last, at minimum, a full day of normal usage (preferably months of use), powering all the IC’s and the display. Secondly, you must meet agency requirements (i.e. FCC/CE/EMI/RFI/USB, etc). Thirdly, if the device has rechargeable batteries, you must be able to safely recharge them. Or alternatively, you must use low cost, disposable batteries. And finally, the handheld device pc board must accommodate many small power conversion devices into a relatively small space and do this efficiently in pc board cm2, power and cost.

A WORD OF This is what could happen if you don’t exercise caution in your power system design Fire reportedly caused by charging a Samsung Galaxy Note 7

Power Considerations for a Handheld Device Power Budget for: Displays and backlighting High powered, high speed microcontrollers Wireless communications (WiFi or Bluetooth LE) Wired communications (USB) Piezo transducers/Sound devices Battery Size and Weight: Small lithium-ion batteries (NiCads in the past) Size versus Power (mAH) versus Cost Rechargeable versus Disposable Lithium-ion batteries Lithium / Manganese Dioxide (Li/MnO2) – (i.e. CR2032) Cost Considerations: Charging circuitry and charger Replacement of disposable batteries Replacement of rechargeable batteries

A Brief Word About Batteries

Considerations in Using Lithium Ion Batteries Not a good end result

Battery Corrosion HP-19C After Cleaning

What Kind of Power Supplies? HP PRIME

HP-35 Power Supply Schematic credit: Kees Vandersanden Photo Credit : Jacques Laporte and Dan Weed

HP-29C Integrated Circuits and Power Supply 3 1 2

2 HP 29C Power Supply PCB Components of HP-29C Power Supply 3.3uF, 10v NPN Transistor Tank oscillator circuit 330pf cap. & 15uH coil 68Ω 10KΩ 10uF, 16v 6.8uF, 10v 2.2uF, 6v 15uF, 10v 2.2KΩ 22uF, 10v 330pf 100pf diode 2 HP 29C Power Supply PCB (Daughter Board)

HP-21, 25 and 29C Power Supply Vss = +6.3vdc Vdisp = +4.4vdc Tank oscillator circuit Vss = +6.3vdc Vdisp = +4.4vdc Vram = +6.5vdc Vgg = -12.5vdc Vbatt-IN= +2.4vdc (switched) Schematic credit: Jacques Laporte

Power Sections Power Needs uC: Multiple power rails Memory Display Backlight USB Charging Circuit +3.7vdc Lithium Ion battery

HP Prime Microcontroller Microcontroller Power Supply Requirements 2 - DC-DC switching regulators 4 – LDO regulators

Contrast and Compare Past with Present Prime 4 different voltages Vbatt = +3.6vdc Vgg = -12 vdc Vcc = +8.2vdc Vss = +6.2vdc +10 different voltages Vbatt = +3.7vdc Vddalive = + 1.2vdc Vddarm = +1.3vdc Vrtc = +3.3vdc Vdda33usb = +3.3vdc Vddi_udev = +1.2vdc Vddsram = +1.8vdc Vdisp = +?? Vbklight = + ?? Vcharger = +3.7vdc Components 2 PNP transistors 7 diodes 1 multiwound transformer Handfull of passives Components Multiple switching regulators Multiple low drop-out regulators Multiple inductors Multiple transistors Multiple diodes Many surface mount passives

Summary and Conclusions As handheld electronics become more complex, so does the power supply circuitry that powers them. Storage devices (batteries) and their charging circuits have been and are becoming a more important part of handheld devices. Monitoring the status and adjusting the charge of the lithium-ion battery is critical. Newer power integrated circuits will be more efficient and new wall chargers must meet low power regulations Never leave uncharged batteries in your calculators for long periods of time or risk battery leakage, outgassing and corrosion of other circuits.

Acknowledgements and Credits Tony Duell (UK) – Information on MoHPC site and email exchange in 2012. Jacques Laporte (r.i.p.) – HP Calculator Forum (www.jacques-laporte.org/forum) email exchange and the papers “The ‘Woodstock’ generation” and “The HP-35 Power Unit”. Museum of HP Calculators – (http://hpmuseum.org) Geoff Quickfall – Email exchange regarding HP calculators, particularly the HP19C. Dave Colver (UK) – Email exchange regarding HP29C schematics. Randy Sloyer – (www.fixthatcalc.com) email exchange in 2012. Eric Smith – Email and posts on MoHPC. Katie Wasserman – email exchange regarding HP29C. Woodbank Communications, Ltd. – Electropaedia Kees Vandersanden. Calculator/power supply website. Personal Collection: HP01, HP10bII, HP12C, HP15CLE, HP17bII+, HP19C, HP21, HP25, HP29C, HP30b, HP32E, HP32SII, HP34C, HP35S, HP41CX, HP42S HP45, HP67, HP97, WP34S, HP Prime

Thank you! © 2016 All rights reserved regarding the information contained in this presentation . If you have any questions you may contact Jim Johnson. Email: jjohnson873@yahoo.com