SC02 Introduction 1 - Philips Semiconductors / NXP Semiconductors

Philips Semiconductors

Power Diodes Introduction

NEW PRODUCTS

Philips Semiconductors are working intensively on

bringing new Power Diode products to the market. The

products listed below appear for the first time in this data

handbook.

25 V SCHOTTKY DIODES

A range of low voltage schottky diodes with a reverse

voltageratingof25 V,withextremelylowforwardvoltage

and ultra fast switching. These products are intended for

use in switched mode power supplies with 3 V and 3.3 V

outputs. They are also ideal for use as or-ing diodes in

fault tolerant designs or current sharing configurations.

Types: BYV116, PBYR225CT, PBYR1025,

PBYR1525CT, PBYR2025CT, PBYR2525CT.

DEFLECTION DIODES

Further extensions to our range of high voltage, fast

recovery diodes, designed for use in the horizontal

deflection stages of multisync computer monitors with

scan rates up to 82 kHz. These devices complement our

range of high voltage bipolar deflection transistors and

have fast forward recovery time, low forward recovery

voltage and reverse voltage ratings up to 1700 V.Types:

BY479X-1700, BY559-1500.

ISOLATED 45 V SCHOTTKY AND 200 V EPITAXIAL DIODES

A wide range of 45 Vschottky diodes and 200 V ultrafast

recovery epitaxial diodes in the SOT186A envelope. This

package is an isolated version of TO220AB with

2500 Vrms isolation between leads and case. Types:

BYV118X, BYV133X, BYV143X, PBYR745X,

PBYR1045X, PBYR1545CTX, PBYR1645X,

PBYR2045CTX, PBYR2545CTX, BYQ28X, BYQ28EX,

BYW29EX, BYV32EX, BYV42EX,

SURFACE MOUNT POWER DIODES IN SOT404

A wide range of schottky and 200 V epitaxial diodes in a

SOT404 envelope suitable for surface mounting. This

package is a surface mounting version of TO220AB with

the same thermal resistance and current rating. Types:

BYV118B, BYV143B, PBYR745B, PBYR1045B,

PBYR10100B, PBYR1545CTB, PBYR1645B,

PBYR2045CTB, PBYR20100CTB, PBYR2545CTB,

BYQ28EB,BYW29EB,BYV32EB,BYV42EB,BYV79EB.

SURFACE MOUNT BREAKOVER DIODES IN SOD106

The BR211 range of breakover diodes in a SOD106

surface mounting envelope. Used for transient

overvoltage protection in line based telecommunications

equipment. BR211SM series.

FORTHCOMING PRODUCTS

The products listed below are planned for release within

the next 12 months, before the next edition of this data

handbook. Contact your Philips Regional or National

Sales office for further details.

SURFACE MOUNT POWER DIODES IN SOT428

Available towards the end of 1996, a range of schottky

and200 VepitaxialdiodesinaSOT428envelopesuitable

for surface mounting. The SOT428 envelope is slightly

larger than our present subminiature surface mounting

package, SOT223 and may be mounted on the same

printed circuit pad layout. However, it has lower thermal

resistance and can accommodate larger crystal sizes,

thereby allowing higher current ratings to be achieved in

a smaller package.

SCHOTTKY AND 200 V EPITAXIAL DIODES IN TO247

Available during the first quarter of 1997, a range of

schottkyand 200 V epitaxial diodesin a TO247 envelope

suitableforhigh powerapplications,featuringlowthermal

resistance and output current ratings up to 60 Amps.

POWER FACTOR CORRECTION DIODES

Available during the first quarter of 1997, a range of

ultrafast, 600 V epitaxial diodes specifically designed for

power factor correction and other forced commutation

applications. These diodes are designed to minimise

switching losses both in the diode and in the switching

transistor.Otherapplicationsincludefreewheelingdiodes

in full and half bridge switched mode power supplies,

where they complement our new range of 400 V, 500 V

and 600 V power mosfets.

APPLICATIONS

Application information for Power Diodes and other

Philips power products is published in Philips Power

Semiconductor Applications Handbook. (Order

code: 9398-652-85011)

September 1996

Philips Semiconductors

Power Diodes Introduction

POWER DIODE CHARACTERISTICS

Back diffused rectifier diodes

A single-diffused P-N diode with a two layer structure

cannotcombine ahighforwardcurrentdensitywithahigh

reverse blocking voltage.

A way out of this dilemma is provided by the three layer

structure, the so-called P-I-N diode, where ’I’ is a lightly

doped (nearly intrinsic) layer. This layer, called the base,

is sandwiched between the highly doped diffused P+and

N+outer layers giving a P+-P-N+or P+-N-N+structure.

Generally, the base gives the diode its high reverse

voltage,andthetwodiffusedregionsgivethehighforward

current rating.

Such a three layer diode can be realised using a

’back-diffused’ structure. A lightly doped silicon wafer is

given a very long N+diffusion on one side, followed by a

relatively shallow P+diffusion on the opposite side. This

asymmetricdiffusionallowsbettercontrolofthethickness

of the base layer than the conventional double diffusion

method,resultinginabettertrade-offbetweenlowforward

voltage and high reverse blocking voltage. Generally, for

a given silicon area, the thicker the base layer the higher

the VRand the lower the IF. Reverse switching

characteristics also determine the base design. Fast

recoverydiodes usuallyhaveN-typebase regions togive

’soft’ recovery with a narrow base layer to give fast

switching.

Ultra fast rectifier diodes

Ultra fast rectifier diodes, made by epitaxial technology,

areintendedfor usein applications wherelowconduction

and switching losses are of paramount importance and

relatively low reverse blocking voltage (VRWM = 150V) is

required: e.g. Switched mode power supplies operating

at frequencies of about 50 kHz.

The use of epitaxial technology means that there is very

close control over the almost ideal diffusion profile and

base width giving very high carrier injection efficiencies

leading to lower conduction losses than conventional

technologypermits. Thewell defineddiffusion profilealso

allowsatightcontrolofstoredminoritycarriersinthebase

region, so that very fast turn-off times (35 ns) can be

achieved. The range of devices also has a soft reverse

recovery and a low forward recovery voltage.

Schottky-barrier rectifier diodes

Schottky-barrier rectifiers find application in low-voltage

switched-mode power supplies (e.g. a 5 V output) where

they give an increase in efficiency due to the very low

forward drop, and low switching losses. Power Schottky

diodes are made by a metal-semiconductor barrier

process to minimise forward voltage losses, and being

majority carrier devices have no stored charge. They are

therefore capable of operating at extremely high speeds.

Electricalperformanceinforwardandreverseconduction

is uniquely defined by the device’s metal-semiconductor

’barrierheight’.Philipsprocessminimisesforwardvoltage

drop, whilst maintaining reverse leakage current at full

rated working voltage and Tj max at an acceptable level.

Philips range of power schottky-barrier diodes can

withstand reverse voltage transients and have

guaranteed reverse surge capability.

Power diode ratings

A rating is a value that establishes either a limiting

capability or a limiting condition for an electronic device.

It is determined for specified values of environment and

operation, and may be stated in any suitable terms.

Limiting conditions may be either maxima or minima.

All limiting values quoted in this data handbook are

Absolute Maximum Ratings - limiting values of operating

and environmental conditions applicable to any device of

a specified type, as defined by its published data, which

should not be exceeded under the worst probable

conditions.

VOLTAGE RATINGS

VRSM Non-repetitivepeakreversevoltage.Themaximum

allowable instantaneous reverse voltage including

all non-repetitive transients. duration ≤ 10 ms.

VRRM Repetitive peak reverse voltage. The maximum

allowable instantaneous reverse voltage including

transients which occur every cycle,

duration ≤ 10 ms, duty cycle ≤ 0.01.

VRWM Crest working reverse voltage. The maximum

allowable instantaneous reverse voltage including

transients which may be applied every cycle

exludingallrepetitiveandnon-repetitivetransients.

VRContinuous reverse voltage. The maximum

allowable constant reverse voltage. Operation at

rated VRmay be limited to junction temperatures

below Tj max in order to prevent thermal runaway.

CURRENT RATINGS

IF(AV) Average forward current. Specified for either

square or sinusoidal current waveforms at a

maximum mounting base or heatsink temperature.

The maximum average current which may be

passedthroughthedevicewithoutexceedingTj max.

IF(RMS) Root mean square current. The rms value of a

current waveform is the value which causes the

same dissipation as the equivalent d.c. value.

IFRM Repetitive peak forward current. The maximum

allowablepeakforwardcurrent includingtransients

which occur every cycle. The junction temperature

should not exceed Tj max during repetitive current

transients.

IFSM Non-repetitive forward current. The maximum

allowable peak forward current which may be

applied no more than 100 times in the life of the

device. Usually specified with reapplied VRWM

following the surge.

September 1996

Philips Semiconductors

Power Diodes Introduction

IRRM Repetitive peak reverse current. The maximum

allowablepeakreversecurrent includingtransients

which occur every cycle.

IRSM Non-repetitive reverse current. The maximum

allowable peak reverse current which may be

applied no more than 100 times in the life of the

device.

Forward current ratings

Theforwardvoltage/currentcharacteristicof adiode may

be approximated by a piecewise linear model as shown

in fig:1. where RSis the slope of the line which passes

through the rated current and VOis the voltage axis

intercept.Theforward voltageisthenVF = VO + IF.RS,and

theinstantaneousdissipation isPF = VO.IF + IF2.RS.where

IFis the instantaneous forward current.

It can be shown that the average forward dissipation for

any current waveform is: PF(AV) = VO.IF(AV) + IF(RMS)2.RS,

where IF(AV) is the average forward current and IF(RMS) is

the rms value of the forward current. Graphs in the

published data show forward dissipation as a function of

average current for square or sinusoidal waveforms over

a range of duty cycles and form factors.

To ensure reliable operation, the maximum allowable

junction temperature Tj max should not be exceeded

repetitively, either as a result of the average dissipation

in the device or as a result of high peak currents

The average junction temperature rise is the average

dissipation multiplied by the thermal resistance; Rth j-mb or

Rth j-hs. Subtracting the junction temperature rise from the

maximum allowable junction temperature Tj max, gives the

maximum allowable mounting base or heatsink

temperature.

The peak junction temperature rise for a rectangular

current pulse may be found by multiplying the

instantaneouspowerbythethermalimpedance.Analysis

methods for non-rectangular pulses are covered in the

Power Semiconductor Applications handbook.

Fig.1. Piecewise linear approximation to diode

forward characteristic.

Power diode characteristics

A characteristic is an inherent and measurable property

ofadevice.Suchapropertymay beexpressedas avalue

for stated or recognized conditions. A characteristic may

alsobe a set ofrelated values, usuallyshown ingraphical

form.

REVERSE RECOVERY

When a semiconductor rectifier diode has been

conducting in the forward direction sufficiently long to

establish the steady state, there will be a charge due to

minority carriers present. Before the device can block in

the reverse direction this charge must be extracted. This

extraction takes the form of a transient reverse current

and this, together with the reverse bias voltage results in

additional power dissipation which reduces the

rectification efficiency. At sine-wave frequencies up to

about 400Hz these effects can often be ignored, but at

higher frequencies and for square waves the switching

losses must be considered. The parameters of reverse

recovery are defined in fig:2.

Stored charge

The area under the IRversus time curve is known as the

stored charge (Qs) and is normally quoted in

microcoulombs or nanocoulombs. Low stored charge

devices are preferred for fast switching applications.

Reverse recovery time

Another parameter which can be used to determine the

speedofthe rectifieristhereverserecoverytime(trr).This

is measured from the instant the current passes through

zero (from forward to reverse) to the instant the current

recovers to either 10% or 25% of its peak reverse value.

Low reverse recovery times are associated with low

stored charge devices.

The conditions which need to be specified are:

a. Steady-state forward current (IF); high currents

increase recovery time.

0VF / V

0 0.5 1.51.0

IF / A

slope Rs

September 1996

Philips Semiconductors

Power Diodes Introduction

b. Reverse bias voltage (VR); low reverse voltage

increases recovery time.

c. Rate of fall of anode current (dIF/dt); high rates of fall

reduce recovery time, but increase stored charge.

d. Junctiontemperature(Tj);hightemperaturesincrease

both recovery time and stored charge.

Fig.2. Definition of t

, Q

and I

rrm

Softness of recovery

In many switching circuits it is not just the magnitude but

the shape of the reverse recovery characteristic that is

important. If the positive-going edge of the characteristic

has a fast rise time (as in a so-called ’snap-off’ device)

this edge may cause conducted or radiated radio

frequency interference (rfi), or it may generate high

voltagesacross inductors which maybe in series with the

rectifier. The maximum slope of the reverse recovery

current (dIR/dt) is quoted as a measure of the ’softness’

of the characteristic. Low values are less liable to give rfi

problems.The measurementconditionswhichneed tobe

specified are as above.

Reverse recovery current

The peak value of the reverse recovery current (Irrm)isan

important parameter in many switched mode power

supply circuits. This is because the high transient current

produced by a diode with a high Irrm can be interpreted by

the circuit as a short circuit fault, which may cause the

power supply to shut down or have apparently poor load

regulation. Like the stored charge and reverse recovery

time, Irrm increases with increasing temperature, so the

effects sometimes only become apparent when the

equipment gets hot. Irrm correlates with stored charge Qs.

Thus choosing an Ultrafast diode with low Qsusually

avoids this problem.

SWITCHING LOSSES

The product of the transient reverse current and the

reversevoltageispowerdissipation,mostofwhichoccurs

whilstthereverse recoverycurrentisdecreasingfrom the

peakvalue(Irrm)tozero.Inrepetitiveoperationanaverage

power can be calculated and added to the forward

dissipation to give the total power. The peak value of

transient reverse current is known as Irrm. The origin of

reverse recovery losses is illustrated in fig:3.

The conditions which need to be specified are:

a. Forward current (IF); high currents increase switching

losses.

b. Rate of fall of anode current (dIF/dt); high rates of fall

increaseswitchinglosses.Thisisparticularlyimportant

in square-wave operation. Power losses in sine-wave

operation for a given frequency are considerably less

due to the much lower dIF/dt.

c. Frequency (f); high frequency means high losses.

d. Reverse bias voltage (VR); high reverse bias means

high losses.

e. Junction temperature (Tj); high temperature means

high losses.

Fig.3. Waveforms showing the origin of reverse

switching losses.

FORWARD RECOVERY

At the instant a semiconductor rectifier diode is switched

into forward conduction there are no carriers present at

the junction, hence the forward voltage drop may be

instantaneously of a high value. As the stored charge

builds up, conductivity modulation takes place and the

forwardvoltage rapidly fallstothesteady state value.The

peakvalueofforwardvoltagedropisknownastheforward

recoveryvoltage(Vfr).Thetimefromtheinstantthecurrent

reaches 10% of its steady-state value to the time the

forward voltagedrops below a given value ( usually5V or

2V)isknownastheforwardrecoverytime(tfr).Theforward

recovery parameters are defined in fig:4.

The conditions which need to be specified are:

a. Forward current (IF); high currents give high recovery

voltages.

b. Current pulse rise time (tr); short rise times give high

recovery voltages.

100%

time

dtF

Irrm

trr

25% or 10%

time

Irrm

trr

-dIF/dt area = Qs

September 1996

Philips Semiconductors

Power Diodes Introduction

c. Junction temperature (Tj); The influence of

temperature is slight.

Fig.4. Definition of V

and t

Breakover diodes

Breakover diodes (BOD’s) are two terminal devices that

operate in either an off (non-conducting) or an on

(conducting) state. A BOD will remain in the off state until

the maximum breakover voltage is applied across its

terminals. A BOD will then conduct with a low on-state

voltage until the current is reduced below the minimum

holding current.

BOD’s are available as Single Symmetric (operation in

1st and 3rd quadrants) in a hermetically sealed axial

leaded SOD84 envelope, and also in a surface mount

SOD106 package. BOD’s are graded according to

breakover voltage.

BREAKOVER DIODE CHARACTERISTICS

Fig.5. Breakover diode symbol and characteristics.

The main characteristics are illustrated in fig:5. These

characteristics are:-

V(BO) Breakover voltage, the maximum voltage

appearing across the BOD before switching to the

on-state.

VDStand-off voltage, maximum normal operating

voltage.

IDOff-state current, normally quoted at VD.

V(BR) Breakdown voltage, below which the BOD will not

go into avalanche breakdown.

I(BR) Breakdown current, with V(BR) applied.

ISSwitching current, the avalanche current required

to switch the BOD to the on-state.

ITOn-state current.

VTOn-state voltage, specified at a given IT.

IHHolding current, the minimum current at which the

BOD will remain in the on-state.

USE OF BREAKOVER DIODES

BOD’s are primarily designed to protect electronic

equipment connected to transmission lines against

transientovervoltages.However,there aremanyusesfor

BOD’s as breakover switches.

In designing BOD circuits the following must be

considered:-

Off-state conditions

VDMust not be exceeded in normal off-state

operation. In the off-state the BOD will not pass

more current than ID.

dVD/dt The rate of rise of voltage must not exceed that

quotedfor the device. Ifthis is exceeded theBOD

may switch to the on-state.

V(BR) To ensure the BOD remains in the off-state, the

voltage must remain below V(BR) min. If this is

exceeded, the BOD will either clip the voltage or

switch to the on-state.

ISIfV(BR) isexceeded butthecurrentlimitedtobelow

ISminimum,the BOD is prevented from switching

to the on-state.

CjThe off-state capacitance across the BOD. In

transmission line protection applications this will

be across the termination of the line.

Switching conditions

V(BO) Atransient voltage greater than V(BO) max is required

to switch the BOD. V(BO) may be greater than the

voltageacrosstheBODwhenitispassingacurrent

of IS max.

ISTo enable the BOD to switch to the on-state a

current greater than ISmaximum is required.

time

Vfr

10%

5V / 2V

tfr

IH V(BO)

current

voltage

Symbol

V(BR)

I(BR)

Symmetric BOD

September 1996

Philips Semiconductors

Power Diodes Introduction

On-state conditions

VTThe on-state voltage is quoted for a given IT

IHTo enable the BOD to switch to the off-state the

current must fall below IHminimum.

ITSM ITSM specifies the rate of rise and duration of a

transient peak on-state current. The waveshape is

definedaccording toCCITTRec. K17, illustrated in

Fig:6. The waveform is referred to as 10/700 µs

waveform.

Fig.6. Definition of I

TSM

waveform.

Thermal conditions

Rth For extended on-state operation ( > 0.1 ms) the

steady-state thermal resistance should be

considered. Total thermal resistance to ambient

should be sufficiently low to dissipate the heat

generated by the device.

Zth If the BOD is used only during transient

overvoltagesthenthe transientthermal impedance

to ambient should be considered.

100%

90%

50%

30%

ITSM

10us 700us time

current

September 1996

Philips Semiconductors

Power Diodes Introduction

QUALITY

Total Quality Management

Philips Semiconductors is

committed to be a world class,

customer driven, volume supplier

of semiconductors.

To achieve this, we operate a Total

Quality Management (TQM)

system, based on Continuous

Improvement and Quality

Assurance in all our business

activities, and Partnerships with

our customers and suppliers.

The top priority throughout the company is Continuous

Improvement.

To focus on this we will:

- Work closely with key customers, as our partners.

- Monitor progress, using customer-driven data, of

our product and services.

- Benchmark against the best.

Furthermore, all parts of the organisation must always

demonstrate:

- The presence of a strong, management-led

improvement structure.

- Commitment and participation in all areas.

- Measurable progress towards our Quality

Improvement goals.

Organisation

An organisation is in place which ensures that personnel

with the necessary organisational freedom and authority

can identify and solve quality problems, prevent

occurrence of product non-conformity and protect the

customer from non-conforming product.

Design control

A comprehensive design and development procedure is

in place which ensures that the requirements of good

design practice are met.

Particular emphasis is placed on ensuring that the initial

specification is agreed by the Customer and the

Marketing and Development functions.

There are regular formal reviews of design progress to

ensure that the initial specification will be met by the

design.

Detailed measurements are made on initial samples to

ensure that the initial specification has been met.

Process control

All processes which directly affect quality are carried out

under controlled conditions. Documented work

instructionsareavailableforallproductionprocessesand

the appropriate environmental controls are in place to

ensure consistent processing. Monitoring of the product,

processes and the environment takes place during

production.

Approval exercises are run to ensure that new processes

and new equipment perform at an acceptable level.

Written, photographicor visual standards are available at

the appropriate points in the production processes.

Corrective action

Non-conforming product found in process is investigated

and the root causes identified. Changes to product or

process are then introduced to prevent recurrence of the

problem.

Quality assurance

Based on ISO 9000 standards, customer standardssuch

as Ford TQE. Our factories are certified to ISO 9000.

Partnerships with customers

These include: PPM co-operations, design-in

agreements, ship-to-stock, just-in-time, self-qualification

programmes and application support.

Partnerships with suppliers

In addition to ISO9000 audits and close monitoring of

supplier delivery performance, we operate a Supplier

Excellence Award scheme which requires suppliers and

their sub-suppliers to use statistical process control,

perform gauge studies and use failure mode and effect

analysis (FMEA) techniques to identify and correct the

root causes of quality and delivery problems.

Product reliability

With the increasing complexity of Original Equipment

Manufacturer (OEM) equipment, component reliability

must be extremely high. Our research laboratories and

development departments study the failure mechanisms

of semiconductors. Their studies result in design rules

and process optimizations for the highest built-in product

reliability. Highly accelerated tests are applied in order to

evaluate the product reliability. Rejects from reliability

tests and from customer complaints are submitted to

failure analysis and the results applied to improve the

product or process.

Customer responses

Our quality improvement depends on joint action with our

customer. We need our customers inputs and we invite

constructive comment on all aspects of our performance.

Please contact your local sales representative.

Recognition

The high quality of our products and services is

demonstrated by many Quality Awards granted by major

customers and international organisations.

QUALITY IMPROVEMENT

PARTNERSHIPS

QUALITY ASSURANCE SYSTEM

TQM

September 1996