Power Sources & Management

ECE 450

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BatteriesAlkaline • Power capacity: Medium*

• Weight: Heavy (30 Watt hours / Kg)• Life cycle: One-time use• Cost: Inexpensive• Energy Output: Very Low• Performance at low charge: Weak• Self discharge rate: Low (< 2% of charge per year)*• Cell Voltage: 1.52V

Lead Acid • Power capacity: Low• Weight: Heavy (30 Watt hours / Kg)• Life cycle: ~800 charges• Cost: Inexpensive• Energy Output: Very Low• Performance at low charge: Weak• Self discharge rate: Low (<0.3% of charge per day) • Cell Voltage: 2V

NiCad

(Nickel Cadmium)

• Power capacity: Medium• Weight: Medium (40 – 60 Watt hours / Kg)• Life cycle: ~1500 charges (memory effect*)• Cost: Inexpensive• Energy Output: Medium• Performance at low charge: Weak (tapers down gradually)• Self discharge rate: Medium (1% of charge per day) *• Cell Voltage: 1.2V

http://www.electrictoolguide.com/types-of-batteries

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Batteries

NiMH (Nickel Metal Hydride)

• Power capacity: High• Weight: Light (60 – 80 Watt hours / Kg)• Life cycle: ~1000 charges• Cost: Medium (some higher capacity models get

expensive)• Energy output: High – appropriate for high-demand applications• Performance at low charge: Strong (dies suddenly)• Self discharge rate: High (4% of charge per day)*• Cell Voltage: 1.2V

Lithium

(Li-ion)

• Power capacity: High – Very High• Weight: Ultra-Light (100+ Watt hours / Kg)• Life cycle: ~1200 charges• Cost: High• Energy Output: High• Performance at low charge: Strong (usually gives a warning before dying)• Self discharge rate: Low (<0.2% of charge per day) *• Cell Voltage: 3.6V

Fuel Cell •Power capacity: 2 to 3 times over Li-ion batteries•Weight: Ultra-Light (100+ Watt hours / Kg)•Life cycle: Refilled with methanol or ethanol•Cost: High ($400)

http://www.electrictoolguide.com/types-of-batteries

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Capacity Discharge vs Voltage

http://www.societyofrobots.com/batteries.shtml

(Alkaline)

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Temperature Effects Lithium Ion Batteries

http://www.societyofrobots.com/batteries.shtml

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Storage CharacteristicsLithium Ion Batteries

http://www.societyofrobots.com/batteries.shtml

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Discharge RatesLithium Ion Batteries

http://www.societyofrobots.com/batteries.shtml

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Alkaline Batteries

Not Fit for High Drain Electronic Devices

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Battery Connections

GND

VCC

VCC

GND

1.5v 1.5v 1.5v 1.5v

28mA

28mA

28mA

28mA

Parallel Connection*

Series Connection

Voltage Regulators

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MC7800, MC7800A, LM340, LM340A Series, NCV7805APPLICATIONS INFORMATION

Design Considerations

The MC7800 Series of fixed voltage regulators are designed with Thermal Overload Protection that shuts down the circuit when subjected to an excessive power overload condition, Internal Short Circuit Protection that limits the maximum current the circuit will pass, and Output Transistor Safe–Area Compensation that reduces the output short circuit current as the voltage across the pass transistor is increased.

In many low current applications, compensation capacitors are not required. However, it is recommended that the regulator input be bypassed with a capacitor if the regulator is connected to the power supply filter with long wire lengths, or if the output load capacitance is large. An input bypass capacitor should be selected to provide good high–frequency characteristics to insure stable operation under all load conditions. A 0.33 F or larger tantalum, mylar, or other capacitor having low internal impedance at high frequencies should be chosen. The bypass capacitor should be mounted with the shortest possible leads directly across the regulators input terminals. Normally good construction techniques should be used to minimize ground loops and lead resistance drops since the regulator has no external sense lead.

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Typical Bases

TO-220 TO-92 8-DIP 8-SMD

IC:

Index Mark

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Schematic for a simple 7805-based power supply

7805

Unr

egul

ated

inpu

t

Gro

und

Reg

ulat

ed O

utpu

t

To Robot Circuits+5 VDC

C11F

C20.1F

+

From 9V batteryOr battery pack

+7 VDC to +20 VDC

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Schematic for a simple 7805-based power supply

7805

Unr

egul

ated

inpu

t

Gro

und

Reg

ulat

ed O

utpu

t

From 9V batteryOr battery pack

+7 VDC to +20 VDCTo Robot Circuits

+5 VDC

C11F

C20.1F

+C3

100F

Circuit Noise

Bypassing is the reduction of high frequency current flow in a high impedance path by shunting that path with a bypass, usually a capacitor. Bypassing is used to reduce the noise current on power supply lines.

Decoupling is the isolation of two circuits on a common line. The decoupling network is usually a low pass filter and the isolation is rarely equal in both directions. Decoupling is used to prevent transmission of noise from one circuit to another. In practice, bypassing is always used when decoupling.

Most circuits require bypassing, not decoupling. Using decoupling techniques to accomplish bypassing will give disappointing, if not disastrous, results. Complete understanding of both concepts is vital.

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16

Schematic for a 7805-based power supply

7805

Unr

egul

ated

inpu

t

Gro

und

Reg

ulat

ed O

utpu

t

From 9V batteryOr battery pack

+7 VDC to +20 VDCTo Robot Circuits

+5 VDC

C11F

C20.1F

+C3

100FC1Bulk

220F+ C1Bulk

220F+

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Types of CapacitorsType Capacitance

RangeMaximum

VoltageAccuracy Temperature

StabilityLeakage Comments

Mica 1pF-0.01F 100-600 Good Good Excellent; good at RF

Tubular ceramic 0.5pF-100pF 100-600 Selectable Several tempcos (including zero)

Ceramic 10pF-1F 50-30,000 Poor Poor Moderate Small, inexpensive, very popular

Polyester (Mylar) 0.001F-50F

50-600 Good Poor Good Inexpensive, good, popular

Polystyrene 10pF-2.7F 100-600 Excellent Good Excellent High quality; large; signal filters

Polycarbonate 10pF-30F 50-800 Excellent Excellent Good High Quality, small

Polypropylene 100pF-50F 100-800 Excellent Good Excellent High quality; low dielectric absorption

Teflon 1000pF-2F 50-200 Excellent Best Best High quality, lowest dielectric absorption

Porcelain 100pF-0.1F 50-400 Good Good Good Good long-term stability

Glass 10pF-1000pF 100-600 Good Excellent Long-term stability

Tantalum 0.1F-500F 6-100 Poor Poor High capacitance; polarized; small; low inductance

Electrolytic 0.1F-1.6F 3-600 Terrible Ghastly Awful Power-supply filters; polarized; short life

Double layer 0.1F-10F 1.5-6 Poor Poor Good Memory backup; high series resistance

Oil 0.1F-20F 200-10,000 Good High-voltage filters; large; long life

Vacuum 1pF-5000pF 2000-36,000 Excellent Transmitters

Capacitor Ratings

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Capacitor Ratings

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20

Diodes

Diode SchottkyDiode

ZenerDiode

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Schematic for a 7805-based power supply Reverse Current Flow Protection

7805

Unr

egul

ated

inpu

t

Gro

und

Reg

ulat

ed O

utpu

t

To Robot Circuits+5 VDC

C11F

C20.1F

+

D11N5817

(Schottky)

From 9V batteryOr battery pack

+7 VDC to +20 VDC

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Schematic for a 7805-based power supplyOverload of Regulated Voltage

7805

Unr

egul

ated

inpu

t

Gro

und

Reg

ulat

ed O

utpu

t

To Robot Circuits+5 VDC

C11F

C20.1F

+

D11N5817

(Schottky)

From 9V batteryOr battery pack

+7 VDC to +20 VDC

ZD15.6V Zener1N5232B

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Improvements to Simple 7805 Voltage Regulator

1. Include the capacitors suggested by the manufacturer. After that, add a bulk capacitor to the regulated output and to the unregulated power supply

2. Use a low-resistance, p-channel power MOSFET to prevent damage from a reverse battery

3. Add various low- and medium-value capacitors of different chemistries and technologies at various places on the circuit board to collectively benefit form their individual strengths.

4. Include at least one 0.1 F capacitor for every chip to bypass board impedance (providing a “local” power supply) and to decouple (isolate and reduce) circuit noise. Put each capacitor as close as possible to its targeted chip, and keep the lead length of each capacitor as short as possible.

5. Add a PPTC overcurrent-protection device to limit the maximum current that can flow through the robot.

6. Add a 5.6 V zener diode to the 5V regulated circuit to prevent damage from overload.

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Improved Schematic for a 7805-based power supply

7805

Unr

egul

ated

inpu

t

Gro

und

Reg

ulat

ed O

utpu

t

battery pack

To Robot Circuits+5 VDC

C11F

C2Bulk

220F

+

D11N5817

(Schottky)

C1Bulk

220F

+ +C2

0.1FZD1

5.6V Zener1N5232B

C41000F

+C4

0.1F

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Butterworth Filters

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