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DC
POWER SUPPLY
HANDBOOK
Application Note 90B
TABLE OF CONTENTS
Introduction ...........................................................................................................................................................6
Definitions ..............................................................................................................................................................6
Ambient Temperature..........................................................................................................................................6
Automatic (Auto) Parallel Operation ..................................................................................................................6
Automatic (Auto) Series Operation.....................................................................................................................7
Automatic (Auto) Tracking Operation ................................................................................................................8
Carryover Time....................................................................................................................................................8
Complementary Tracking ....................................................................................................................................8
Compliance Voltage ............................................................................................................................................8
Constant Current Power Supply ..........................................................................................................................8
Constant Voltage Power Supply..........................................................................................................................9
Constant Voltage/Constant Current (CV/CC) Power Supply..............................................................................9
Constant Voltage/Current Limiting (CV/CL) Power Supply ............................................................................10
Crowbar Circuit .................................................................................................................................................11
Current Foldback ...............................................................................................................................................11
Drift....................................................................................................................................................................11
Efficiency...........................................................................................................................................................11
Electromagnetic Interference (EMI)..................................................................................................................11
Inrush Current ....................................................................................................................................................11
Load Effect (Load Regulation)..........................................................................................................................12
Load Effect Transient Recovery Time ..............................................................................................................12
Off-Line Power Supply......................................................................................................................................12
Output Impedance of a Power Supply ...............................................................................................................12
PARD (Ripple and Noise) .................................................................................................................................13
Programming Speed...........................................................................................................................................14
Remote Programming (Remote Control)...........................................................................................................14
Remote Sensing (Remote Error Sensing) ..........................................................................................................15
Resolution ..........................................................................................................................................................15
Source Effect (Line Regulation)........................................................................................................................15
Stability (see Drift) ............................................................................................................................................16
Temperature Coefficient....................................................................................................................................16
Warm Up Time ..................................................................................................................................................16
Principles of Operation.......................................................................................................................................17
Constant Voltage Power Supply........................................................................................................................17
Regulating Techniques...................................................................................................................................18
Series Regulation ...........................................................................................................................................18
Typical Series Regulated Power Supply........................................................................................................19
Pros and Cons of Series Regulated Supplies .................................................................................................19
The Series Regulated Supply - An Operational Amplifier ............................................................................20
Series Regulator with Preregulator ................................................................................................................23
Switching Regulation .....................................................................................................................................25
Basic Switching Supply .................................................................................................................................26
3
Typical Switching Regulated Power Supplies ...............................................................................................27
Summary of Basic Switching Regulator Configurations ...............................................................................30
SCR Regulation..............................................................................................................................................31
Constant Current Power Supply ........................................................................................................................32
Constant Voltage/Constant Current (CV/CC) Power Supply............................................................................34
Constant Voltage/Current Limiting Supplies ....................................................................................................36
Current Limit..................................................................................................................................................36
Current Foldback............................................................................................................................................37
Protection Circuits .............................................................................................................................................38
Protection Circuits for Linear Type Supplies ................................................................................................38
Overvoltage Crowbar Circuit Details ............................................................................................................39
Crowbar Response Time ................................................................................................................................41
Special Purpose Power Supplies........................................................................................................................43
High Voltage Power Supply...........................................................................................................................43
High Performance Power Supplies ................................................................................................................45
Extended Range Power Supplies ...................................................................................................................50
Advantages of Extended Range .....................................................................................................................50
Example of Extended Range Power Supply ..................................................................................................51
Faster Down-Programming Speed .................................................................................................................53
Bipolar Power Supply/Amplifier ...................................................................................................................54
Digitally Controlled Power Sources ..............................................................................................................55
AC and Load Connections..................................................................................................................................59
Checklist For AC and Load Connections ..........................................................................................................59
AC Power Input Connections.........................................................................................................................59
Load Connections for One Power Supply......................................................................................................59
Load Connections for Two or More Power Supplies ....................................................................................60
AC Power Input Connections ............................................................................................................................60
Autotransformers ...........................................................................................................................................61
Line Regulators ..............................................................................................................................................61
Input AC Wire Rating ....................................................................................................................................61
LOAD CONNECTIONS FOR ONE POWER SUPPLY...................................................................................61
DC Distribution Terminals.............................................................................................................................62
Load Decoupling............................................................................................................................................64
Ground Loops.................................................................................................................................................65
DC Common ..................................................................................................................................................68
DC Ground Point............................................................................................................................................72
Remote Error Sensing (Constant Voltage Operation Only)...........................................................................72
Load Connections For Two or More Power Supplies .......................................................................................78
DC Distribution Terminals.............................................................................................................................78
DC Common ..................................................................................................................................................79
DC Ground Point............................................................................................................................................79
Remote Programming.........................................................................................................................................80
Constant Voltage Remote Programming With Resistance Control...................................................................80
Remote Programming Connections ...............................................................................................................81
Output Drift....................................................................................................................................................81
Protecting Against Momentary Programming Errors ....................................................................................82
Backup Protection for Open Programming Source........................................................................................83
4
Constant Voltage Remote Programming With Voltage Control .......................................................................84
Programming with Unity Voltage Gain .........................................................................................................84
Programming with Variable Voltage Gain ....................................................................................................85
Constant Current Remote Programming............................................................................................................86
Remote Programming Accuracy........................................................................................................................86
Remote Programming Speed .............................................................................................................................88
Output Voltage and Current Ratings................................................................................................................91
Duty Cycle Loading...........................................................................................................................................91
Reverse Current Loading...................................................................................................................................93
Dual Output Using Resistive Divider ................................................................................................................94
Parallel Operation ..............................................................................................................................................96
Auto Parallel Operation .....................................................................................................................................96
Series Operation ................................................................................................................................................97
Auto-Series Operation .......................................................................................................................................97
Auto Tracking Operation...................................................................................................................................99
Converting a Constant Voltage Power Supply To Constant Current Output ....................................................99
PERFORMANCE MEASUREMENTS ..........................................................................................................101
Constant Voltage Power Supply Measurements..............................................................................................101
Precautions ...................................................................................................................................................101
CV Source Effect (Line Regulation)............................................................................................................104
CV Load Effect (Load Regulation)..............................................................................................................104
CV PARD (Ripple and Noise) .....................................................................................................................105
CV Load Effect Transient Recovery Time (Load Transient Recovery)......................................................109
CV Drift (Stability) ......................................................................................................................................111
CV Temperature Coefficient........................................................................................................................111
CV Programming Speed...............................................................................................................................111
CV Output Impedance..................................................................................................................................113
Constant Current Power Supply Measurements ..............................................................................................113
Precautions ...................................................................................................................................................114
CC Source Effect (Line Regulation)............................................................................................................116
CC Load Effect (Load Regulation) ..............................................................................................................116
CC PARD (Ripple and Noise) .....................................................................................................................116
CC Load Effect Transient Recovery Time ..................................................................................................117
CC Drift (Stability) ......................................................................................................................................117
CC Temperature Coefficient........................................................................................................................119
Other Constant Current Specifications ........................................................................................................119
Index ...................................................................................................................................................................120
5
INTRODUCTION
Regulated power supplies employ engineering techniques drawn from the latest advances in many disciplines
such as: low-level, high-power, and wideband amplification techniques; operational amplifier and feedback
principles; pulse circuit techniques; and the constantly expanding frontiers of solid state component
development.
The full benefits of the engineering that has gone into the modern regulated power supply cannot be realized
unless the user first recognizes the inherent versatility and high performance capabilities, and second,
understands how to apply these features. This handbook is designed to aid that understanding by providing
complete information on the operation, performance, and connection of regulated power supplies.
The handbook is divided into six main sections: Definitions, Principles of Operation, AC and Load
Connections, Remote Programming, Output Voltage and Current Ratings, and Performance Measurements.
Each section contains answers to many of the questions commonly asked by users, like:
What is meant by auto-parallel operation?
What are the advantages and disadvantages of switching regulated supplies?
When should remote sensing at the load be used?
How can ground loops in multiple loads be avoided?
What factors affect programming speed?
What are the techniques for measuring power supply performance?
In summary, this is a book written not for the theorist, but for the user attempting to solve both traditional and
unusual application problems with regulated power supplies.
DEFINITIONS
AMBIENT TEMPERATURE
The temperature of the air immediately surrounding the power supply.
AUTOMATIC (AUTO) PARALLEL OPERATION
A master-slave parallel connection of the outputs of two or more supplies used for obtaining a current output
greater than that obtainable from one supply. Auto-Parallel operation is characterized by one-knob control,
equal current sharing, and no internal wiring changes. Normally only supplies having the same model number
may be connected in Auto-Parallel, since the units must have the same IR drop across the current monitoring
resistors at full current rating.
6
AUTO-PARALLEL POWER SUPPLY SYSTEM
AUTOMATIC (AUTO) SERIES OPERATION
A master-slave series connection of the outputs of two or more power supplies used for obtaining a voltage
greater than that obtainable from one supply. Auto-Series operation, which is permissible up to 300 volts off
ground, is characterized by one-knob control, equal or proportional voltage sharing, and no internal wiring
changes. Different model numbers may be connected in Auto-Series without restriction, provided that each
slave is capable of Auto-Series operation.
AUTO-SERIES POWER SUPPLY SYSTEM
7
AUTOMATIC (AUTO) TRACKING OPERATION
A master-slave connection of two or more power supplies each of which has one of its output terminals in
common with one of the output terminals of all of the other power supplies. Auto-Tracking operation is
characterized by one-knob control, proportional output voltage from all supplies, and no internal wiring
changes. Useful where simultaneous turn-up, turn-down or proportional control of all power supplies in a
system is required.
AUTO-TRACKING POWER SUPPLY SYSTEM
CARRYOVER TIME
The period of time that a power supply's output will remain within specifications after loss of ac input power. It
is sometimes called holding time.
COMPLEMENTARY TRACKING
A master-slave interconnection similar to Auto-Tracking except that only two supplies are used and the output
voltage of the slave is always of opposite polarity with respect to the master. The amplitude of the slaves' output
voltage is equal to, or proportional to, that of the master. A pair of complementary tracking supplies is often
housed in a single unit.
COMPLIANCE VOLTAGE
The output voltage rating of a power supply operating in the constant current mode (analogous to the output
current rating of a supply operating in the constant voltage mode).
CONSTANT CURRENT POWER SUPPLY
A regulated power supply that acts to maintain its output current constant in spite of changes in load, line,
temperature, etc. Thus, for a change in load resistance, the output current remains constant while the output
voltage changes by whatever amount necessary to accomplish this.
8
CONSTANT CURRENT POWER SUPPLY
OUTPUT CHARACTERISTICS
CONSTANT VOLTAGE POWER SUPPLY
A regulated power supply that acts to maintain its output voltage constant in spite of changes in load, line,
temperature, etc. Thus, for a change in load resistance, the output voltage of this type of supply remains
constant while the output current changes by whatever amount necessary to accomplish this.
CONSTANT VOLTAGE POWER SUPPLY
OUTPUT CHARACTERISTIC
CONSTANT VOLTAGE/CONSTANT CURRENT (CV/CC) POWER SUPPLY
A power supply that acts as a constant voltage source for comparatively large values of load resistance and as a
constant current source for comparatively small values of load resistance. The automatic crossover or transition
between these two modes of operation occurs at a "critical" or "crossover" value of load resistance Rc = Es/Is,
where Es is the front panel voltage control setting and Is is the front panel current control setting.
9
CONSTANT VOLTAGE/CONSTANT CURRENT
(CV/CC) OUTPUT CHARACTERISTIC
CONSTANT VOLTAGE/CURRENT LIMITING (CV/CL) POWER SUPPLY
A supply similar to a CV/CC supply except for less precise regulation at low values of load resistance, i.e., in
the current limiting region of operation. One form of current limiting is shown above.
CONSTANT VOLTAGE/ CURRENT LIMITING
(CV/CL) OUTPUT CHARACTERISTIC
10
CROWBAR CIRCUIT
An overvoltage protection circuit that monitors the output voltage of the supply and rapidly places a short
circuit (or crowbar) across the output terminals if a preset voltage level is exceeded.
CURRENT FOLDBACK
Another form of current limiting often used in fixed output voltage supplies. For load resistance smaller than
the crossover value, the current, as well as the voltage, decreases along a foldback locus.
DRIFT
The maximum change in power supply output during a stated period of time (usually 8 hours) following a
warm-up period, with all influence and control quantities (such as; load, ac line, and ambient temperature)
maintained constant. Drift includes periodic and random deviations (PARD) over a bandwidth from dc to 20Hz.
(At frequencies above 20Hz, PARD is specified separately.)
EFFICIENCY
Expressed in percent, efficiency is the total output power of the supply divided by the active input power.
Unless otherwise specified, Agilent measures efficiency at maximum rated output power and at worst case
conditions of the ac line voltage.
ELECTROMAGNETIC INTERFERENCE (EMI)
Any type of electromagnetic energy that could degrade the performance of electrical or electronic equipment.
The EMI generated by a power supply can be propagated either by conduction (via the input and output leads)
or by radiation from the units' case. The terms "noise" and "radio-frequency interference" (RFI) are sometimes
used in the same context.
INRUSH CURRENT
The maximum instantaneous value of the input current to a power supply when ac power is first applied.
11
LOAD EFFECT (LOAD REGULATION)
Formerly known as load regulation, load effect is the change in the steady-state value of the dc output voltage
or current resulting from a specified change in the load current (of a constant-voltage supply) or the load
voltage (of a constant-current supply), with all other influence quantities maintained constant.
LOAD EFFECT TRANSIENT RECOVERY TIME
Sometimes referred to as transient recovery time or transient response time, it is, loosely speaking, the time
required for the output voltage of a power supply to return to within a level approximating the normal dc output
following a sudden change in load current. More exactly, Load Transient Recovery Time for a CV supply is the
time "X" required for the output voltage to recover to, and stay within "Y" millivolts of the nominal output
voltage following a "Z" amp step change in load current --where:
TRANSIENT RECOVERY TIME
(1) "Y" is specified separately for each model but is generally of the same order as the load regulation
specification.
(2) The nominal output voltage is defined as the dc level halfway between the steady state output voltage
before and after the imposed load change.
(3) "Z" is the specified load current change, typically equal to the full load current rating of the
OFF-LINE POWER SUPPLY
A power supply whose input rectifier circuits operate directly from the ac power line, without transformer
isolation.
OUTPUT IMPEDANCE OF A POWER SUPPLY
At any frequency of load change, EOUT/IOUT. Strictly speaking, the definition applies only for a sinusoidal
load disturbance, unless the measurement is made at zero frequency (dc). The output impedance of an ideal
constant voltage power supply would be zero at all frequencies, while the output impedance for an ideal
constant current power supply would be infinite at all frequencies.
12
TYPICAL OUTPUT IMPEDANCE OF A CONSTANT
VOLTAGE POWER SUPPLY
PARD (RIPPLE AND NOISE)
The term PARD is an acronym for "Periodic and Random deviation" and replaces the former term ripple and
noise. PARD is the residual ac component that is superimposed on the dc output voltage or current of a power
supply. It is measured over a specified bandwidth, with all influence and control quantities maintained constant.
PARD is specified in rms and/or peak-to-peak values over a bandwidth of 20Hz to 20MHz. Fluctuations below
20Hz are treated as drift. Attempting to measure PARD with an instrument that has insufficient bandwidth may
conceal high frequency spikes that could be detrimental to a load.
DC OUTPUT OF POWER SUPPLY AND
SUPERIMPOSED PARD COMPONENT
13
PROGRAMMING SPEED
The maximum time required for the output voltage or current to change from an initial value to within a
tolerance band of the newly programmed value following the onset of a step change in the programming input
signal. Because the programming speed depends on the loading of the supply and on whether the output is being
programmed to a higher or lower value, programming speed is usually specified at no load and full load and in
both the up and down directions.
PROGRAMMING SPEED WAVEFORMS
REMOTE PROGRAMMING (REMOTE CONTROL)
Control of the regulated output voltage or current of a power supply by means of a remotely varied resistance or
voltage. The illustrations below show examples of constant voltage remote programming. CC applications are
similar.
REMOTE PROGRAMMING USING RESISTANCE CONTROL
REMOTE PROGRAMMING USING VOLTAGE CONTROL
14
REMOTE SENSING (REMOTE ERROR SENSING)
A means whereby a constant voltage power supply monitors and regulates its output voltage directly at the load
terminals (instead of the power supply output terminals). Two low current sensing leads are connected between
the load terminals and special sensing terminals located on the power supply, permitting the power supply
output voltage to compensate for IR drops in the load leads (up to a specified limit).
POWER SUPPLY AND LOAD CONNECTED NORMALLY
POWER SUPPLY AND LOAD CONNECTED FOR REMOTE SENSING
RESOLUTION
The smallest change in output voltage or current that can be obtained using the front panel controls.
SOURCE EFFECT (LINE REGULATION)
Formerly known as line regulation, source effect is the change in the steady-state value of the dc output voltage
(of a CV supply) or current (of a CC supply) due to a specified change in the source (ac line) voltage, with all
other influence quantities maintained constant. Source effect is usually measured after a "complete" change in
the ac line voltage; from low line to high line or vice-versa.
15
STABILITY (SEE DRIFT)
TEMPERATURE COEFFICIENT
For a power supply operated at constant load and constant ac input, the maximum steady-state change in output
voltage (for a constant voltage supply) or output current (for a constant current supply) for each degree change
in the ambient temperature, with all other influence quantities maintained constant.
WARM UP TIME
The time interval required by a power supply to meet all performance specifications after it is first turned on.
16
PRINCIPLES OF OPERATION
Electronic power supplies are defined as circuits which transform electrical input power--either ac or dc--into
output power--either ac or dc. This definition thus excludes power supplies based on rotating machine
principles and distinguishes power supplies from the more general category of electrical power sources which
derive electrical power from other energy forms (e. g., batteries, solar cells, fuel cells).
Electronic power supplies can be divided into four broad classifications:
(1) ac in, ac out-line regulators and frequency changers
(2) dc in, dc out-converters and dc regulators
(3) dc in, ac out-inverters
(4) ac in, dc out
This last category is by far the most common of the four and is generally the one referred to when speaking of a
"power supply". Most of this Handbook is devoted to ac in/dc out power supplies, although a brief description
of a dc-to-dc converter is presented later in this section.
Four basic outputs or modes or operation can be provided by dc output power supplies: