๐Electronics & Circuit Design
Power Supply Design
Linear Regulator Dropout
5V regulator with 2V dropout
Output voltage: 5V (5,000 mV)
Dropout voltage: 2V (2,000 mV)
Min input:
Recommended input: 9V for margin
Max input: 35V (thermal limiting)
Use 9V wall adapter
Switching Regulator Efficiency
Buck converter 12V โ 3.3V at 1A
Input: 12V ร 0.33A = 4W (theoretical)
Output: 3.3V ร 1A = 3.3W
Efficiency: 85% typical
Actual input:
Input current:
Much better than linear
Sensor Interface Design
ADC Input Scaling
0-10V sensor โ 0-3.3V microcontroller
Sensor range: 0-10V (0-10,000 mV)
MCU ADC range: 0-3.3V (0-3,300 mV)
Scale factor:
Voltage divider: R1=6.7kฮฉ, R2=3.3kฮฉ
Test: 10V input โ 3.3V output
Safe for 3.3V MCU
Thermocouple Amplification
K-type: 41ยตV/ยฐC, need 0-5V for 0-1000ยฐC
Max signal:
Required gain:
Op-amp gain:
For gain=122: Rf=121kฮฉ, Rg=1kฮฉ
Cold junction compensation needed
Use specialized TC amp IC
๐Battery & Portable Applications
Battery Voltage Monitoring
Li-ion Battery Management
18650 cell voltage monitoring
Fully charged: 4.2V (4,200 mV)
Nominal: 3.7V (3,700 mV)
Low warning: 3.3V (3,300 mV)
Cutoff: 3.0V (3,000 mV)
Over-discharge damage: <2.5V
3S pack: 3 ร 3.7V = 11.1V nominal
Monitor per-cell voltage
Lead-Acid Battery States
12V automotive battery analysis
Fully charged: 12.6V (12,600 mV)
75% charge: 12.4V (12,400 mV)
50% charge: 12.2V (12,200 mV)
25% charge: 12.0V (12,000 mV)
Discharged: 11.8V (11,800 mV)
Load test: 10.5V minimum under load
Replace if <10.5V under load
Power Management ICs
USB Power Delivery
USB-C PD voltage selection
Standard USB: 5V (5,000 mV)
PD Profile 1: 9V (9,000 mV)
PD Profile 2: 15V (15,000 mV)
PD Profile 3: 20V (20,000 mV)
Laptop charging: typically 20V ร 3A = 60W
Phone fast charge: 9V ร 2A = 18W
Negotiate optimal voltage
Boost Converter Design
3.7V battery โ 5V USB output
Input range: 3.0-4.2V
Output: 5V ยฑ 5% (4.75-5.25V)
Output current: 1A maximum
Efficiency: ~90% at full load
Input current:
Size inductor for 1.5A
โกPower Systems & Electrical Safety
Voltage Classifications
Extra Low Voltage
<50V
<50,000 mV
Generally safe to touch
Low Voltage
50-1000V
0.05-1 kV
Household & commercial
High Voltage
>1000V
>1 kV
Industrial & transmission
International Voltage Standards
Residential Voltages
USA/Canada: 120V/240V (split-phase)
Europe/Asia: 230V (single-phase)
Japan: 100V (unique standard)
UK: 240V (legacy, now 230V)
Travel adapters change plugs, not voltage!
Industrial 3-Phase
USA: 208V, 480V, 4160V
Europe: 400V (line-to-line)
Distribution: 4-35 kV
Transmission: 115-765 kV
Line voltage = Phase voltage ร โ3
โCommon Voltage Conversion Mistakes
Mistake #1: Confusing RMS and Peak Values
Wrong: 120V outlet has 120V peak
Right: 120V RMS = 170V peak (โ2 ร RMS)
AC voltages are typically specified as RMS values
Mistake #2: Ignoring Voltage Drop
Wrong: Long wire has same voltage at both ends
Right: I ร R drop reduces voltage along wire
Use larger wire gauge for long runs or high currents
Mistake #3: Mixing DC and AC Values
Wrong: 12V DC = 12V AC (for power calculations)
Right: Specify DC or AC RMS clearly
12V DC and 12V AC RMS have very different peak values