Help with power supply design for portable device

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SUMMARY

This discussion focuses on designing a power supply for a portable medical research device intended for small rodents, requiring multiple voltage outputs: 3.3 V, +/- 1.5 V, and +/- 20 V. The device's digital components include an MCU and a Bluetooth module, while the analog components operate on dual power supplies. The user seeks guidance on the optimal use of LDOs, switching, and linear regulators, as well as recommendations for achieving the +/- 20 V output efficiently. Key considerations include power efficiency, PCB size, and minimizing noise in data sampling circuits.

PREREQUISITES
  • Understanding of power supply design principles
  • Familiarity with LDO and switching regulator technologies
  • Knowledge of PCB design constraints and efficiency optimization
  • Experience with battery selection for portable devices
NEXT STEPS
  • Research the use of LDOs versus switching regulators for low-noise applications
  • Explore methods for generating +/- 20 V from a 3.6 V LiPo battery
  • Investigate PCB layout techniques to minimize noise in analog circuits
  • Utilize power supply simulation tools like TI's WEBENCH or PowerESim for design iterations
USEFUL FOR

Engineers and designers involved in portable medical device development, particularly those focusing on power supply design, efficiency optimization, and noise reduction in analog signal processing.

jibjab123
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I need help designing a power supply for a portable medical research device for animals. My problem is designing a configuration for multiple voltages with pcb size and power efficiency in mind. I need 3.3 V, +/- 1.5 V, and +/- 20 V.

Below I’ve listed device info and estimated current consumption of both the analog and digital components.

Device Info: My device will be worn by small rodents and used to (1) amplify low-voltage and low frequency (< 15 kHz) analog signals, (2) output 100uA@20V constant current pulses, and (3) communicate with PC via BT. This device will be small (2’x2’ double sided pcb) and light weight. Thus, efficiency and pcb footprint are extremely important. Component cost isn’t much of a concern.

Digital Components:
1. MCU: 10 mA @ 3.3 V (Supply Range: 1.7 - 5.0 V )
2. Bluetooth Module: 15 mA @ 3.3V (Supply Range: 3.0 - 3.6 V, peak current 50mA)

Analog Components: All analog components use dual power supplies (+/-).
1. Section A: 1mA @ +/- 1.5 V (<1% duty cycle, Supply Range: 1.0 - 3.3 V)
2. Section B: 2mA @ +/- 20.0 V (1% duty cycle)

Battery: I was hoping to use a 3.6 V LiPo battery unless there is a more appropriate battery or source voltage.

Questions: Where and how should I use LDO, switching, or linear regulators together for this application? What’s the best way to get the +/- 20 V? Should I adjust any component supply voltages for higher efficiency? ... etc...? Any help would be tremendously appreciated.
 
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There are several free on-line or downloadable design/simulators specifically for power supplies. I'm sure you will need to balance overall weight/size/power consumption, and simulations can be helpful in quickly running numerous design iterations to compare results.

A few to get you started:
http://www.ti.com/ww/en/analog/webench/power.shtml
http://www.poweresim.com/
http://www.fairchildsemi.com/design_tools/

Don't forget that switching supplies may introduce noise in your data sampling circuits.
 
jibjab123 said:
My device will be worn by small rodents ... This device will be small (2’x2’ double sided pcb) ...

Big rodents. :devil:
 

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