tds-029 issue 01 (350a power considerations) issue 01 (350a power considerations).pdf• no network...

ZIZTEL LIMITED

email: [email protected] web: www.ziztel.com tel: +44 (0) 115 9202888 mail: 96 Rolleston Drive, Arnold, Nottingham, NG5 7JP United Kingdom

All text, drawings and photography contained within this data sheet are the property of Ziztel Ltd and are Subject to copyright. Information may neither be transmitted or copied

to third parties without the express written consent of Ziztel Ltd.Ziztel Ltd have a policy of continuous product improvement and contents here in are liable to change without

notice.

350A AMPLIFIER POWER LOADING

TDS-029 Issue 01 Ziztel Technical Bulletin

350A POWER CONSUMPTION

Background

In a PAGA system the biggest consumers from the mains supply are:

i. The audio power amplifier

ii. The flashing beacons when fitted (used to deliver visual

annunciation in high ambient noise areas).

Considering the power amplifier consumption.

The signals delivered by either the system microphones or alarm tone

generator are incapable of driving the site loudspeaker networks directly due

to:

i. The voltage amplitude is too small (typically below one volt).

ii. The current source/sink is also very small - of the order of

milliamperes.

The amplifier therefore provides both voltage and current amplification; in

the case of the 350A amplifier module the voltage is amplified to nominal

100VRMS and current drive capability is 3.5Amperes enabling loudspeaker

loads of up to 350Watts to be driven by audio bandwidth program input.

The energy delivered by the amplifier in to the loudspeaker load is sourced

from the system mains supply input. The mains supply required by the

amplifier is DC Direct Current and where the supply is AC a rectifier is

interposed to provide the necessary conversion to DC. This supply is

modulated by the output stage in the amplifier with the power drive available

being limited by a number of factors including the capabilities of the output

stage transistors, line transformer and power supply.

Thank you for your interest in

Ziztel - we are a UK based

manufacturer of PAGA/MBS and

Intercom products. Our systems

are mainly designed for use in

the Military, Marine, Hazardous

Oil, Gas and Petrochemical

industries.

Amongst the other

telecommunication packages

required for effective site

communications the Public

Address and General alarm

broadcast system is one of the

major power consumers. Power

management within the Ziztel

system is carefully controlled to

maximise efficiency thereby

reducing the impact on the site

UPS and battery units. By

increasing efficiency less wild

heat is dissipated and so HVAC

requirements are reduced

accordingly. Major power

consumers in a PAGA system are

the loudspeaker power amplifiers

which can vary in assignment to

a few hundred Watts to systems

capable of delivering tens of

thousands of Watts. This paper

provides detail of the 350A

amplifier power consumption.

ZIZTEL LIMITED




notice.

Typical PAGA central rack employs Ziztel 350A Class G amplification.

Efficiency

The efficiency of the power amplifier is determined by the amount of power consumed from the mains supply versus the

amount of audio power delivered to the loudspeaker network load. The efficiency can never be 100%, i.e. 100Watts consumed

by the amplifier converted to 100Watts of loudspeaker audio drive as there are inevitable losses taking place in the

conversion. The lost power, in the main, is dissipated as wild heat. The efficiency of an audio amplifier varies depending on

the design of the output stage and this is defined by the mode of operation selected by the designer.

There are a number of design possibilities which are defined by ‘Class’:-

Class A employs a linear design which is only about 10% efficient, i.e. for every 100Watts of power consumed from the mains

supply only 10Watts is delivered as audio power to the load. This topology is used in HiFi amplifiers.

• Linear single-ended; the amplifier device is biased about the centre of the input signal swing.

• The output device carries the entire cycle.

ZIZTEL LIMITED




notice.

• Very low efficiency – best efficiency 10%.

• High heat emission – most of the power input is converted to wild heat.

• Physically much larger equipment due to heat sinks, fans, power supplies.

• Not used for PAGA due to poor conversion efficiency.

• Used for top end HiFi applications due to exceedingly low distortion.

Class B is again a linear design but employs a push/pull output stage to improve efficiency – greater than 50% but suffers

from high distortion and unsuitable for audio applications.

• Linear ‘Push-pull’ output stage comprises of two output devices – one device handles the positive signal half-

cycle, second device handles the negative signal half-cycle.

• Low efficiency – best efficiency approximately 50%.

• High heat emission – 50% of power input is converted to wild heat.

• Physically much larger equipment due to heat sinks and power conversion.

• Large UPS power requirement, larger batteries, more expensive.

• High cross over distortion due to transfer characteristics of output transistors.

Class AB is a refinement of Class B and provides bias to improve the distortion caused by the non-linearity in the output

device transfer function. This class is commonly used in audio applications.

ZIZTEL LIMITED




notice.

• Class B topology but with small standing current in output transistors to ‘bias’ the devices into the linear region

of the transfer characteristics.

• Used in high fidelity applications, public address, PAGA, music systems, etc...

• Low efficiency – best efficiency 50%.

• High heat emission – 50% of power input is converted to wild heat.

• Physically much larger equipment due to heat sinks and power conversion.

• Large UPS power requirement, larger batteries, more expensive. Low distortion, high linearity.

Class D uses pulse width modulation to increase efficiency to theoretical 90% - extensively used in audio applications but

suffers from EMC and line matching problems in PAGA applications with attendant impact on efficiency and RF radiation

risk.

• Switch mode Amplifier utilises a pulse width modulated carrier high frequency square wave.

• Theoretical higher efficiency - claimed up to 90% conversion.

• Transistors are driven into saturation or fully cut off and are usually arranged in an ‘H’ bridge.

ZIZTEL LIMITED




notice.

• Efficiency not always realised in practice due to inability to match the varying field network impedances.

• EMC radiated radio frequency risk. Class D is an ideal topology for fixed load systems – example music systems

where speaker assignment is predictable, home cinema amplifiers again when the speaker load characteristics

are known.

• Class D is not usually specified for top end HiFi audio systems where purists claim that Class A is sonically

superior.

Class G uses a linear output stage with a power supply optimised to the program input efficiency 85% - ideal for audio

applications.

• High efficiency - 85% conversion.

• Linear output stage as Class A+B but with switched power supply rails to improve efficiency.

• Smaller UPS/Battery requirements.

• No high frequency carrier, no associated EMC issue.

• No network matching problems associated with Class D designs

The Ziztel amplifier employs Class G technology.

Class H is similar to Class G, but power supply control samples the incoming audio signal at several more positions to

further improve efficiency.

ZIZTEL LIMITED




notice.

Quiescent power consumption

With no program signal applied (speech or alarm tones) there is a standing current consumed by the amplifier. In the case of

350A this is 24Watts. The relationship between quiescent power consumption and maximum power consumption is not

linear and as load is increased the power drawn in quiescent contributes progressively less to the overall power consumption.

With no load connected and signal drive applied, the amplifier will draw power from the supply and this is almost double the

quiescent current, in this case approximately 40Watts. Again the relationship between ‘no load’/full load power consumption

is not linear.

Power consumption

Consumption off load and idle:- 24Watts Wild heat 20Watts

Consumption off load and ‘driven A’*:- 40Watts Wild heat 30Watts

Consumption 100Watt load and idle:- 24Watts Wild heat 20Watts

Consumption 100Watt load and ‘driven A’*:- 130Watts Wild heat 25Watts

Consumption 100Watt load and ‘driven S’**:- 60Watts Wild heat 20Watts

Consumption 350Watt load and idle:- 24Watts Wild heat 20Watts

Consumption 350Watt load and ‘driven A’*:- 400Watts Wild heat 45Watts

Consumption 350Watt load and ‘driven S’**:- 140Watts Wild heat 35Watts

* ‘Driven A’ is defined as a continuous alarm tone delivered in to the loudspeaker load specified.

** ‘Driven S’ is defined as continuous speech average delivered in to the loudspeaker load specified.

Wild heat is heat wasted in the conversion of mains supply power to audio drive power to the loudspeakers. The heat is

dissipated on the 350A amplifier heatsink which is vented by convection.

tds-029 issue 01 (350a power considerations) issue 01 (350a power considerations).pdf• no network...

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