1. 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

2. 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.

3. 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

4. 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

5. A Brief Word About
Batteries

6. Considerations in Using Lithium Ion Batteries
Not a good
end result

7. Battery Corrosion HP-19C
After
Cleaning

8. What Kind of Power Supplies?
HP PRIME

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

10. HP-29C Integrated Circuits and Power Supply3 1 2

11. 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)

12. 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

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

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

15. 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 = vdc
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

16. 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.

17. Acknowledgements and Credits
Tony Duell (UK) – Information on MoHPC site and exchange in 2012.
Jacques Laporte (r.i.p.) – HP Calculator Forum ( exchange and the papers “The ‘Woodstock’ generation” and “The HP-35 Power Unit”.
Museum of HP Calculators – (
Geoff Quickfall – exchange regarding HP calculators, particularly the HP19C.
Dave Colver (UK) – exchange regarding HP29C schematics.
Randy Sloyer – ( exchange in 2012.
Eric Smith – and posts on MoHPC.
Katie Wasserman – 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

18. Thank you!
© 2016 All rights reserved regarding the information contained in this presentation .
If you have any questions you may contact Jim Johnson.