|
|
|
|
Usage of Thermo-sensitive
devieces and Thermisitors 1 |
|
|
 |
Thermo-sensitive devices, where to use |
|
There are several types of such resistors
that change resistance with the temperature. As an example, to switch control
an equipment to a preset temperature, negative temperature coefficient (NTC)
thermistor NT73, is used because
it has a merit in sensitivity rather than linearity.
(Application example) Thermistor as a sensor to switch(on/off) control IC |
|
Another example to use such a device is a
temperature compensator. Linear positive temperature coefficient (PTC) resistor LA73 is
conveniently used to linearly control the circuits, devices, etc. The resistor
as a sensor and the device to be controlled should be thermally tightly coupled.
(Application example)
LA73 is used as the bias resistor
and output load resistor for temperature compensation of high frequency amplifiers. |
|
|
|
Temperature compensation of high frequency amplifiers |
|
This is the example of mobile power stage
amplifiers. When the temperature of the FET is raised, drain current will be
increased. The positive temperature coefficient (PTC) resistor LA73(Rc
in the figure) is coupled to the FET to increase the resistance value. Then
the bias voltage is modified in such a way to decrease the drain current. Thus
the drain current is kept stable by the negative feedback. |
|
|
|
Temperature compensation of Hall elements |
|
A hall element is a sensor, sensitive to the
magnetic field. It is used as the non-contact current probe for oscilloscope,
a non-contact potentiometer, etc.. For a GaAs type element, however, it has
a temperature coefficient of around -600ppm/ max, which needs to be compensated.
A typical application circuit is shown. The Hall element is fed with a constant
current and a differential voltage will be derived proportional to the applied
magnetic field. This voltage is amplified and just compensated by the Rc, which
is the specifiable linear positive temperature coefficient (PTC) resistor LT73 or
LA73. |
|
 |
| |
Temperature compensation of Hall Element |
|
|
|
Temperature compensation of Optical pick-up |
|
The sensitivity of a PIN photo-diode device
is affected so greatly by the temperature that it is a prerequisite to be compensated.
An example of a photo pick-up is shown in the figure, where the linear positive
temperature coefficient resistor LA73 is
used.
R1 is for reverse bias current to the PIN photo-diode, and Rc adjust the gain
of the amplifier by the equation G=R3/(R2+Rc).
This equation means that the effect
of compensation can be adjusted less sensitively in the direction to be weaken
by the series resistor R2.
Note that Rc should be thermally close coupled to
the PIN photo-diode. |
|
 |
| |
Temperature compensation of Optical pick-up |
|
|
Application Notes
Brush up your circuit
Basic Knowledge
