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Being an electronics hobbyist, I'm having quite a challenge to design a PSU, which must run both on batteries (during the night time) as well as on Solar energy (daytime). The device is intend to run 3x brushless motors daily, while in night-time it should keep the telemetry alive.

enter image description here

What I'm particularly worried about the design:

  • a) Is there anything I could improve about the common-ground design? The logic-level transistors sit on the low-side, while I must monitor voltage levels of both - the battery and the Solar array
    simultaneously. My common ground solution looks like a poor-mans
    approach, since voltage drop in the circuit is significant even with Schotkys.
  • b) what's the best method of sucking all the current out of Solar
    cells, while prioritizing the 3V & 5V devices over the motors &
    charger? The transistors introduce huge energy waste due to heat
    while in ohmic region.

The components chosen:

  • transistors: IRLZ44N and MTP3055VL
  • for gate controll I've chosen a digital potentiometer: MCP4261
  • uC: Atmega328P
  • voltage sensing via MUX: CD4067BE
  • current sensing via HALL: ACS712

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  • \$\begingroup\$ If you complete your registration, you should be able to accumulate reputation and get some better access to the site. (Your profile shows you as 'unregistered'.) Once you hit 10 points (which is fairly easy) things improve greatly. \$\endgroup\$ – Adam Lawrence Oct 5 '12 at 12:37
  • \$\begingroup\$ This isn't a full-on answer, but is there a reason you didn't go with a straight-forward ORing setup that utilizes a MOSFET to keep switching losses low? Maybe feed that into a buck/boost converter so you have a single feed to your subsystems? Add charging circuitry that sits behind the ORing setup and charges when needed/possible? I may be overlooking something here but the common rails seem awfully confusing and complicated to me. \$\endgroup\$ – Toby Lawrence Oct 5 '12 at 14:45
  • \$\begingroup\$ @Madmanguruman - thanks for advise, I hit 11, its fine now! \$\endgroup\$ – FlegmatoidZoid Oct 5 '12 at 20:49
  • \$\begingroup\$ @Toby - I did some reading on "ORing". I think I do understand the benefit, but not for MOSFET losses. In respect to LMxxx impulse stabilizers, the bottom and the top MOSFETs in my case are "always on" and aren't switching anything. Then, if I convert their function to become similar to switched DC/DC converter, it looses it's current control ability. Could you please clarify? \$\endgroup\$ – FlegmatoidZoid Oct 5 '12 at 20:50
  • \$\begingroup\$ Right, so... what I'm suggesting is to keep both power sources behind a single regulator. This would equate to using the solar panel to charge the battery (when its output was high enough) while the battery supported the load. You can still monitor the battery and the solar panels independently. As far as prioritizing power delivery, this is something you could handle in the ATmega itself. Monitor the regulator input voltage and when you get to a measured point of discharge, turn off the motors. \$\endgroup\$ – Toby Lawrence Oct 5 '12 at 21:51
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You may want to consider how the IC boost converters for PV panels work, such as the SPV1020 using high side switching and common grounds. The MPPT function shunts the PV to sense voltage drop under a pulse load to detect the power available (Interrogate & Observe algorithm). Considering all the modes of operation, with monitoring & protection circuits and losses is not a trivial design. You have a done a good job in your block diagram, but I agree more work still is needed to reduce the switching losses on your common ground. ( Is that a positive ground?) Diode losses can be reduced by using higher voltage batteries and lower currents.

STMicroelectronics SPV1020 PowerSSO-36 package for ceramic caps and 4 phase current switches. $14 a pc. 9A max 98% eff max.

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links: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00275733.pdf

http://www.st.com/internet/com/SALES_AND_MARKETING_RESOURCES/MARKETING_COMMUNICATION/FLYER/flspv1020.pdf

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