Product Application Guide- Transducers- External Drive-
Electromagnetic
Part Numbering System
Transducer Series (PB)
Part Number Structure PB – 1224 P E-05 Q
Series
PB = Electromagnetic
Unique Identifier
Drive Type & Termination
P = External Drive & PC Pins
Special Designator
RoHS: Q = RoHS Compliant
Part Number Structure AST 605 TR Q
Series: AST = Surface Mount
Unique Identifier
Termination: TR = Tape-N-Reel
RoHS: Q = RoHS Compliant
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Decibel Sound Level Scale
The decibel sound level scale is an arbitrary scale that ranges from 0 dB (threshold of
hearing) to 130 dB (threshold of pain). The chart below shows where some common
sounds fall on this dB scale. Audible alarms are available that have sound levels as soft
as 55 dB at 2 feet and as loud as 110 dB at 2 feet.
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Fundamental Frequency & Harmonics
Below is a frequency scan of a piezoelectric audible alarm that has a resonant frequency
of 2,800 Hz. As you can see, there is a strong frequency peak at 2.8 kHz and several
smaller frequency peaks that follow called harmonic frequencies. The table below the
chart shows that the size of the harmonic frequencies are significantly smaller than the
fundamental frequency for this particular alarm unit. Because this alarm has a large
fundamental frequency and much smaller harmonic frequencies, the sound quality of this
part will be very good. When this alarm is activated, the listener will hear one clear
frequency (also called sound pitch) from the alarm. Other electronic alarm technologies
such as electro-magnetic or electro-mechanical type alarms often have much larger
harmonic frequency components resulting in less clear tone.
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Driving Electromagnetic Transducers
Electromagnetic transducers utilize electromagnets that enable these devices to produce
low sound frequencies in small package sizes. The penalty is that these devices require
more current to work, have limited voltage ratings, and the electromagnetic coil can
create voltage spikes; which, makes the circuit designer’s job more challenging.
The following two circuits are self-contained in that the circuit produces the sine wave
type signal required by the buzzer. The circuit challenge is to set the value of the
capacitors, resistors, and/or inductors to produce the rated buzzer oscillating frequency.
The following three circuits provide a means to drive the electromagnetic transducer
buzzer, but they require an input signal to turn the drive circuitry off and on at the
appropriate rated buzzer frequency. Care must be taken not to over-voltage the buzzer.
The input signal to the previous three drive circuits can come from a microcontroller
output or from a logic circuit similar to the following:
Page 5
The capacitor and resistors values need to be set to provide a signal at the appropriate
rated buzzer frequency. For example, if the electromagnetic buzzer is rated at 2.3 KHz,
then the output signal’s frequency from the microcontroller or from the above circuit
needs to be at 2.3 Khz.
The inductors needed for some of the above circuits may need to handle large current
values and may need to have large inductance ratings. The inductance ratings needed can
range from 1 milli-Henry (1000 uH) to 100 milli-Henry (100000 uH).
One source for these types of inductors is:
Bourns- JW Miller Inductors (www.bourns.com)
Product Series: JW Miller 5900 Series High Current Chokes
(http://www.bourns.com/pdfs/5900_series.pdf)
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- All P/N’s
Part Number
Tube
Count
Reel
Count
Part Number
Tube
Count
Reel
Count
ASI301Q
35
AST612Q
35
ASI301TRQ
250
AST612TRQ
450
ASI401Q
35
AST7525MATRQ
1000
ASI401TRQ
250
PB-1220PQ
40
AST100Q
25
PB-1221PQ
40
AST100TRQ
500
PB-1224PE-05Q
40
AST1109MLTRQ
1000
PB-12N23P-01Q
40
AST1240MLTRQ
1000
PB-12N23P-03Q
40
AST1440MATRQ
600
PB-12N23P-05Q
40
AST1575BMATRQ
300
PB-12N23P-12Q
40
AST1628MATRQ
800
AST1750MATRQ
400
AST200Q
48
AST200TRQ
1000
AST501Q
35
AST501TRQ
450
AST605Q
35
AST605TRQ
300
