2/22/11 Physics 262 Lecture 6 Power Supplies and Regulatorssolar.physics.montana.edu/kankel/ph262/RBnotes/phsx262_S... · 2012-01-06 · Based with permission on lectures by John

Based with permission on lectures by John Getty

Physics 262 Laboratory Electronics II Spring 11 Lecture 6 Page 1

Today• 2/22/11 Physics 262 Lecture 6• Power Supplies and Regulators

– Transformers– Rectifiers– Power supplies and regulators

• Reading– Reread 28-29 (1.17) and 44-48 (1.25-1.29)– Read 52 (1.31), 307-311 (6.01-6.02) and 325-333

• Homework due 3/11. Exercises 1.27 (p. 46), 6.1 (p. 311), and chapter 6 additional exercise 1 ( p. 384)2. Choose a filter capacitor BFPS supplied by a 10:1 transformer with 120 Vrms input voltage to the

transformer has less than 0.5V peak to peak ripple.3. A 1:2 transformer is supplied with Vrms =120V input and has a 1k ohm load. What are the power

dissipated into load, the RMS voltage on load, and the peak current in the primary and the secondary coils?

4. The typical line AC voltage of Vrms =120V followed by with a 1:20 turn ratio transformer supplies a BFPS (with typical 0.6V diodes) and 500 ohm load and 1mF capacitor. What is the output ripple?

• Lab– Lab 5 Power supplies– Do pre-lab BEFORE lab– Lab 4 write-up due Friday at 10am



TransformerVin

.

N1 N2

PrimaryCoil

SecondaryCoil

Rload

2

1out in

NV VN

Vin Vout

1

2out in

Ni iN

out inP P

2

1

NTurn RatioN

A.k.a N2:N1



Bridge Rectifier

Positive half-cycle: Current flows through D1, Rload and D3

Negative half-cycle: Current flows through D2, Rload and D4

V1T1 ..

1

2

4

3

D1

C1Vout

10:1

+

-

D1 D2

D3D4

Rloadi

iiload

Note in both directions, there are two diode voltage drops



V1T1 ..

1

2

4

3

D1

C1Vout

10:1

+

-

D1 D2

D3D4

Brute Force Power Supply

Rload

Filtered Output Voltage

_ max 2 1 _ _ max( / ) 2Out AC in diodeV N N V V

The output is the amplitude of the input, divided by the turns ratio of the transformer minus drop across the rectifier diodes.

Charging Current

iloadic

ic

Charging Current

Unfiltered output from Bridge

Note polarity of electrolytic capacitor



Ripple Voltage

Vbfps

18Vdc

Rload

0

Output Voltage

Vbfps

18Vdc

Rload

0

dVi Cdt

DCripple

V ti tVC RC

rippleV

1Let 1 , , 1000120LOADR k t C F

Hz

18 0.15120 1 1000ripple DC

VV Vk F

t_ maxDCV

For small ripple, VDC ~ VDC_maxBFPS has filter

capacitor, C


Load and Line Regulationload regulation“Change in output voltage or current for any load change within ratings”

line regulation:

“Change in output voltage or current for any line change within ratings.”



0

2

4

6

8

10

12

14

16

1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5 1E+6

Load Resistance

Out

put V

olta

geBFPS has Poor Load Regulation

Parasitic resistance associated with the elements in the circuit all contribute to a relatively large Thévenin equivalent resistance.

V115V

R1

2ohm

Thévenin Equivalent



BFPS has Poor Line Regulation

Changes in line voltage propagate directly through to the load.

V1T1 ..

1

2

4

3

D1

C1Vout

10:1

+

-

Rload

_ _ 2DC out AC line ratio diodeV V T V



Summary of BFPS Characteristics

• Poor line and load regulation

• High current capacity (“ampacity”)

• Inexpensive

V1T1 ..

1

2

4

3

D1

C1Vout

10:1

+

-

Rload

• Large ripple voltage amplitude“Bulk” DC



Regulator

Regulated DC Supply

BFPS

Load

Error Amplifier

Reference(V or I)

Pass Element Filter



Ref_Zener

Rv_ref1

2

3Error_Amp

Pass_Transistor

Current_Limit

Rcl

R1

R2

Rload

Vbfps

Vout

C_filter

Basic Positive Linear Regulator

Reference Voltage

Pass Element

Load

• Small output ripple• Pass element in regulator dissipates energy

Filter

Error Amp

•BFPS powers zener, amp, and trans•Zener produces Vref => Vin+•R1 & R2 scales Vout for input to Vin-•Error amp adjusts pass trans•Current limited by V across Rcl•C_filter helps get rid of ripple•Vout independent of Rload, to a point



723 Regulator

Reference Voltage

Error Amp

Pas

s E

lem

ent

Pins 1, 8 and 14

2 3

4

56

7 9

10

1112

13

No Connection

Vref nominally is 7.15VBut ranges from 6.8 to 7.5V

Vreg max is 37V

Vc > V reg + 3 Vand Vc > 9.5V to power reference



723 Regulator Plus Power Pass Transistor

Error Amp

Pas

s E

lem

ent

2 3

4

56

7 9

10

1112 13

1 TP5

Vreg

1 TP1

Vcc

Q1

TIP31

IN+5

IN- 4VOUT10

VZ9

COMP13

VREF 6

ILIM 2

ISENSE3

VC 11

V+12

V- 7

U1LM723R11.5

R2TBD

R3TBD

Vz

Vout

0

0

VrefVilim

Vin-

C21n

1 TP7

GND

10W, 10%

LM723 Regulator

Pass Trans

Rcl

From BFPS

•BFPS supplies Pass Trans and 723•R2 & R3 scale Vreg for input to Vin-

For Vref > Vout > 2V, divide Vref down•Vref goes into Vin+•723 Vout turns on power Pass Trans•Power pass trans supplies current to Vreg•Pass Trans current limited by voltage across Rcl

Set for 0.5V across Rcl at max current.•Add C_filter of 0.01-0.1uF ceramic and 1-10uF electrolytic



CV and CC Modes5Vdc Source

-10

0

10

-10 0 10

Volts

Am

ps

DC voltage source

5Adc Source

-10

0

10

-10 0 10

Volts

Amps

DC Current Source

IV diagrams



Practical Voltage/Current SourceMost laboratory supplies will “fold back” from constant voltage mode into constant current as required by the load. The point at which the supply converts from constant voltage to constant current is often controllable.

Ideal CV supply can source infinite current.

amps

volts

Practical CV supply is generally protected by limiting output power. Could include “crowbar.”

Lab source folds back at the current limit set point, and is then said to be operating in “constant current” mode.

constant current

cons

tant

vol

tage



References1. Paul Horowitz and Winfield Hill (1989). “The Art of Electronics,” 2nd

Ed., Cambridge2. Roland E. Thomas and Albert J. Rosa (1998). “The Analysis and

Design of Linear Circuits,” 2nd Ed., Prentice Hall 3. Abraham I. Pressman (1998). “Switching Power Supply Design,” 2nd

Ed., McGraw-Hill4. Service Guide Agilent E3631A DC Power Supply

http://cp.literature.agilent.com/litweb/pdf/E3631-90011.pdf

References



Load Regulation

Load Regulation for the Agilent E3631A: Voltage <0.01% + 2 mVCurrent <0.01% + 250 A

Output Ratings (@ 0 °C - 40 °C)+6V Output 0 to +6 V ; 0 to 5 A+25V Output 0 to +25 V ; 0 to 1 A-25V Output 0 to -25 V ; 0 to 1 A

load re·gu·la·tion1. “Change in output voltage or current for any load

change within ratings” 2. ±(% of output + offset)

vout 25V

v vout 0.0001 2mV

vmin vout v vmin 24.995V

vmax vout v vmax 25.005V

vline = 115 +/- 10% VAC



Line Regulationline re·gu·la·tion:

1. “Change in output voltage or current for any line change within ratings.”

Line regulation for the Agilent E3631A: Voltage <0.01% + 2 mVCurrent <0.01% + 250 A

AC Input Rating (line): 115Vrms ±10%

2. “bedding material for a large member of the feline genus”

2. ±(% of output + offset)

vline = 115 +/- 10% VAC



Power Supply Terminology I



Power Supply Terminology II



Power Supply Terminology III



Power Supply Terminology IV

Documents

2/22/11 Physics 262 Lecture 6 Power Supplies and Regulatorssolar.physics.montana.edu/kankel/ph262/RBnotes/phsx262_S... · 2012-01-06 · Based with permission on lectures by John