pixels square 3D image array with <5 cm ranging
accuracy, in real time at rates up to 30 Hz, is designated.
3.2 Power Driving Circuit for Laser Diode
A laser diode accompanying with its power supply is an
important part of LIDAR system onboard UAV. The
traditional power supply had problems in efficiency and
bulk, has been demonstrated that it is not proper for
application on a small low-cost civilian UAV platform.
How to design a power supply for laser diode to meet the
requirement of light, small, and energy efficiency, is a
valuable work. In this paper, a novel power supply
topology for LiDAR system on board UAV platform is
presented. The power supply is composed of two coupled
coils, pulse generator circuit, and a fast switch (Zhou and
Yang, 2011).
Coffey (2009) though that the power-supply largely
impacts the performance of laser-diode for a given
specification. Different methods of design and
implementation of the laser diode power supply have
been proposed by Cui et al. (2011), Zhou et al. (2011),
Yang et al. (2011). A novel low power supply for DC-
coupled 1.25 Gb/s laser diode driver is suggested by Fu
et al. (2006). With the MAX797, driver circuit of the
high-power laser diode was proposed by Li and Xu
(2008). For a pulsed power modulated for high output
power for laser fuze was proposed by Guo et al. (2011).
The automatic power control of DC-coupled burst-mode
laser diode was presented by Zhang et al. (2009) and Li
et al. (2008).
A proposed schematic diagram of the power supply for laser
diode is depicted in Figure 7. As seen from Figure 7,
Driving power supply is composed of two coupled coils
(could be replaced by a pulsed transformer), a thyristor,
TTL pulse signal, resister and capacitor [3-6]. With this
topology of power supply, the input voltage of the power
supply is a *28 V DC voltage from airplane, and the
output maximum voltage is 300 V. Before the TTL pulse
signal coming, the power supply is in a steady state.
During this steady state, capacitor C1 is charged by the
input voltage through R1 and L1 to +28V; the thyristor
QI is turn off because the TTL pulse signal is in a low
state; there is no current in L2; and the output voltage is
0. If a pulse signal comes to the gate of the thyristor QI,
Q1 will turn on, and C1 will release its energy through
Q1 and L1 rapidly cause the low resistance in the circuit.
This situation will generate a high voltage across L2; for
L1 and L2 are strongly coupled. The voltage across L2
can be controlled through turns ratio of L2 and L1, here
we should choose a turns ratio of 10. Assuming the other
parameters of the two inductors are all the same besides
the turns ratio, the inductance of L2 will be 100 times
larger than L1. The generated pulsed voltage is around
300 V (voltage of L1 plus L2). The voltage generated by
L2 is coupled to laser diode D1 through R2 and C2.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B3, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
CI C2
RI i 12 R2
IE ————dr ee
| ^n
| Q (n A
; =e
- Bl E: à À |
e | IT
Figure 7. Schematic diagram of the power supply for laser
diode
In order to meet the requirement of laser diode adopted in
LiDAR scanner onboard small UAV platform, the
parameters of each circuit elements have been specified
and are depicted in Figure 8. Instead of traditionally
trying every element parameter one by one, a circuit
model by PSpice is set up and simulation experiment is
conducted. This method is fast and cost efficiency.
C1
2 2 1
IC - 28
(Cval1)
1mH C3
(Cval2)
Q1
BT151
2
[R] Ki | PARAMETERS:
K Linear zb Cval1 = 100U
“0
Cval2 = 100p
= COUPLING = 1
L1
V1=0V
V2 =5V
PW = 5US
PER = 100US
L2
Figure 8. Simulation model of the power supply for laser diode
With the above design, experiments and test, a prototype
of power supply is produced, as shown in Fig. 9. The
prototype of power supply is synchronous with a pulse
signal generated by control circuit, and the output voltage
and current adjustable to fit laser diode, and the repeat
pulse generation is up to 1000 pulses per second.
Figure 9. A prototype of power supply
4. SIMULATED EXPERIMENTS AND RESULTS
Experiments with simulating different flight height is
conducted. One of experimental results with a flight
height of 200 m is shown in Figure 10. As seen from
Figure 10, the shape of footprint is a square with a size of
at 4398.031 mm x 4398.031 mm in x and y axes,
respectively, which is close to the theoretic size of 4.5 m.
The difference between practice and theoretic values is
102 mm. However, it is estimated that practical error may
be
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