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General Digi-Key Component Parameters
* What’s the best DIP packages/cases (8, 10, 12, 16, etc)?
ANS: There are no best DIP packages/cases to worry about. As a hobbyist/student DIP packages are the
easiest to work with because they are well suited for wire wrapping and prototyping/bread-boarding. DIP
chip sockets are are available at places like Radio Shack and digikey. Sockets are used to all you to wire
wrap to the socket instead of the chip, so that if the chip goes bad, you don't need to change your wiring, just
the chip. In terms of the number of pins, don't worry about that. You will not be approaching any pin count
that would be hard to work with.
* What’s the best packaging (bulk, tube, etc)?
ANS: I assume you are referring to how to order the parts. Well since you only need a limited supply, then
I imagine you want a tube of parts. A tube is typically a plastic container filled with the chips. Bulk refers
to many chips. Often times chips in bulk are sold in what in known as a tape reel. Machines load these
reels and then place chips onto the circuit boards.
PWM
There are 2 types of PWMs:
1) 12v PWM
2) 9.7v – 18v PWM
* Is there enough output from the PWM to power the FET?? How much output voltage is needed from the
PWM?
I need to look up the parts and get back to you on it.
DC to DC CONVERTERS
* Do we want IC or power supply buck and boost converters? As of right now we have IC selected.
* How many output pins are needed for each converter?
It isn't really a function of how many output pins, but rather how much current the part will supply on the
pin.
- Do we need exactly one pin for each component? OR is it possible to feed multiple
components from one output pin?
Basically, the dc-dc converters produce a voltage and current. You do not need one pin per
component, but rather you need to determine how much current each component will draw that
uses that particular voltage. If the total current drawn by all components on that voltage rail is
less than the current output of the dc-dc converter, then you are safe. If it is greater, then you
need to choose a dc-dc converter with a greater current output or you will need to use multiple
dc-dc converters. Personally, I don't think you will have that issue.
* Does it conserve more power to keep decreasing the voltages (48  12  5) or does it matter if we use 48
 5  12?
In your case, I don't think it will matter. There will be a loss due to conversion in both cases and the
difference, is probably minimal.
Op Amp Constraints
* We know we should know this… but what is the Op Amp for?
Well, Op Amps have many different applications. Often times they are used to take a very small
signal and amplify it. Sometimes, op-amps are used for math functions such as addition and
subtraction. I would have to check your schematic to see the manner in which it is
being used, but I suspect that you are taking a small signal and making it larger so
that it will be detected by the processor. In other words, it is probably a small signal that needs
to be translated in to a TTL level signal 0 - 5 volts.
* So, is the Norton op-amp ok to use? (see below)
1) Norton Operational Amplifier – LM3900 – Single Supply of 4.5v – 32v
* NOTE: This Op Amp can use either the +5v or +12 output pins
48v from
Solar Panels
48v from
Solar Panels
DC to DC
Converter
DC to DC
Converter
+5v To PIC, D/A, RS232, OpAmp
+5v
DC to DC
Converter
+12v To PWM
+12v To PWM
+12v
DC to DC
Converter
+5v
To PIC, D/A, RS232, OpAmp
2) Regular Op-Amp (+/- Supply Voltage)
48v from
Solar Panels
DC to DC
Converter
+5v
To PIC, D/A, RS232
+5v
DC to DC
Converter
+10v
To PWM, OpAmp
-10v
Diodes
* Why are there 4 diodes used in the example design after the inductor….and why 2 after the voltage
divider?
* What is the difference between the two types of diodes the example design uses and why would one
use the specific type in each location?
Inductor
We want a coil with the lowest possible on resistance. However, we also want to make sure we have
enough inductance for when the current flows through the inductor to the diodes. We cannot find a way to
understand how much inductance would be necessary for our case.
Voltage Dividers
* What is the resistance for the voltage dividers (what resistors)?
MOSFET
We know we want a FET with low resistance to prevent energy from being lost. We found a FET that
has the lowest on channel resistance currently on the market (HAT2096H)
* What do you think about this one?
http://www.renesas.com/avs/resource/japan/eng/pdf/transistor/e2081431_hat2096h.pdf
* How do we determine the ideal voltage and current of the FET?
MOSFET Driver
We are a little confused about what type to get since we are unsure of the voltage and current that goes
with the FET
PIC Software Program
* Is there enough storage capacity to store EEPROM program in PIC?
I need to look at the PIC, but I suspect the answer is yes. I will try to get back to you on the questions
that I couldn't answer right away. Hopefully this afternoon I can get to it. If not, then I will get to it
tomorrow.
RS232
We are going to use the RS232 serial connection available on the PIC. With this, we will be able to
closely follow the IV curve showing the output from the solar array.
* Do we need to purchase any separate items for this – such as the rs232 cable to connect the PIC to the
computer?
MPPT Algorithm
Function – Access to Solar Array
Function – Access to Battery Array
Function – Access to the DAC controlling the PWM
LOOP: every X seconds
1. Pull instantaneous values:
array output voltage (Vin)
array output current (Iin)
Vin
Solar
Array
Vout
MPPT
Iin
Iout
Battery
Array
battery input voltage (Vout)
battery input current (Iout)
2. Compare Iout to its preceding value
If Iout is increasing, means Vin is approaching maximum power point.
If Iout is decreasing, means Vin is leaving maximum power point.
3. Adjust Vin accordingly.
Sending an appropriate voltage level to the DAC controlling the PWM can do this.
4. Record Vin and Iout
Brief Algorithm Explanations
Step 1: The built-in ADCs provide the PIC16F458 with 10-bit sampled values of Vin, Iin, Vout, and Iout.
Step 2 & 3: The maximum power point (Vmpp) can be approached from the left (Vin < Vmpp) or from the right
(Vin > Vmpp). We have to make sure that the tracker does not move Vin in the wrong direction in the process
of finding maximum power point.
Step 4: It is necessary to keep track of the output power trends and the movement of Vin, because it forms the
basis for future adjustments to the array voltage.