8. Block diagram

The driver block diagramme (pulse power supply) DLT-37 is presented in

fig.12.

The pulse power supply of light-emitting diodes functionally consists of

generator G, single-shot multivibrator M, multiplexer MX1, voltage-to-current

converterv U/I, multiplexer MX2, analog-to-digital converter ADC, liquid crystal

display LCD, the pulse power supply converter of Peltier element DRVP, the pulse

power supply converter DC/DC.

The generator G forms the pulse sequence with variable repetition rate. The

repetition rate can be changed with the help of the button "Frequency". It's

indicated by light-emitting diodes “2 kHz”, “4 kHz”, “8 kHz”, “16kHz”. The

waiting multivibrator M and the multiplexer MX1 receive the voltage impulses in

the form of a meander from the generator G .

The single-shot multivibrator M generates voltage impulses with the

adjustable fixed duration synchronously with rise-up portion of input voltage

impulses. Switching of duration of impulses is carried out by means of the switch

SW1 in the range from 0,6 to 20 µс.

The multiplexer MX1 by means of the button “Operating mode” switch the

clock pulses on the input of voltage-to-current converter U/I. In addition, clock

pulses come to the jack “Synchro” for synchronisation with the external

photoreception amplifier.

The IR-light-emitting diode LED recive a pulse current from U/I converter.

Start-up of circuit U/I is carried out by means of the button “Curent ON/OFF”. The

green light-emitting diode “Work” lights up in that case . If the circuit of the LED

is broken the light-emitting diode “Break” lights up. Adjustment of the amplitude

The circuit executed on DRVP, A2, A3 is used for stabilisation and

adjustment of LED temperature. Stabilisation and temperature adjustment is carried

out by means of Pelte element P. The temperature sensor is based on the

thermoresistor RT. After amplification by A2 the signal from the temperature

sensor supplies on the first input of the error amplifier A3. The reference voltage

DRVP generates the voltage on the Peltier element which changes the temperature

DRVP begin working after pressing the button "Cooler ON / OFF". Then cooling is

working the light-emitting diode “Cooling” is shining . Integrated temperature

controller allows to maintain the temperature of LED in the range from -10 ° C to

+25 ° C.