ELM185xB Laser Diode Driver
• Pulse drive wave
This drive wave is tested base upon standard circuit (4) under the conditions that R1=22kΩ, R2=2.2Ω,
R3=220kΩ, VR1=0, C1=3300pF, C2=1μF, V1=3.6V
ch3
ILM wave= current wave
ch2
AMD wave
ch1
control signal pulse in
Ch1 2.00V/div
Ch3 100mV/div
Ch2 500mV/div
50.0μs/div
Drive circuit with detection circuit of single fault mode)
■Application circuit example 3 (
Based on different applications of laser, it is required that laser output can be maintained in safety region when
single fault error happens. The example of single fault detection circuit is shown as application circuit (5).
If any of following 3 conditions happens, laser output of ELM185xB will be overmuch when single fault of all
pin occurs:
1) Ground short fault happens to KLD (Ground current will be flowed directly from laser and thus result in
overmuch of laser diode light output.)
2) Ground short fault happens to AMD (laser diode light output will be overmuch since output is judged to be 0)
3) VCC short fault happens to CMP (laser diode light output will be overmuch since circuit cannot be controlled.)
If any of these 3 conditions is detected, laser drive will be stopped forcibly and become single fault detection
circuit. Meanwhile, the condition when single fault occurs is the same as initial power input, solutions (start-up
circuit) of error detection for normal action when the circuit starts is required additionally.
For example of this safety circuit, please refer to application (5).When abnormality occurs, ELM742B, the
comparator will detect the error, the latch which is composed by ELM7SU04BW will be turned reversely,
and ELM33405CA, P-ch MOS will be off and thus shut down the power. When comparison voltage of
3 comparators is under 0.9V of KLD, under 0.1V of AMD, and above 2.5V of CMP, it will be judged as
abnormality by OR condition of the comparator and thus the power will be shut down. This circuit is only for
reference use; confirmation of safety standard fit actions on actual application is still required.
Start-up circuit consists of time constant of R1 and C1.The ratio of disperse voltage of R3, R4, R5, R8 is
required to be changed with power voltage. For best solution, ELM recommends using ELM742B as the
voltage detector, ELM7SU04BW as the latch and ELM33405CA as the transistor.
This circuit is for reference use only; additional inspection of safety standard suitableness is required.
It is possible to insert detection circuit as shown in circuit (2) and (3) in this circuit.
10 - 7
ELM-TECH [ ELM Technology Corporation ]
