Design and Implementation of Power Supply of High-Power Diode Laser of LiDAR onboard UAV Jiazhi Yang1, Guoqing Zhou1,2*, Xinchen Yu1, and Wei Zhu1 1
Guangxi Key Laboratory for Spatial Information and Geomatics Guilin University of Technology, Guilin 541004, China Phone: +86-15078372228, E-mail:
[email protected]
2
Department of Modeling, Simulation and Visualization, Old Dominion University Norfolk, Virginia, 23529, USA * Phone:+86-15078372228, E-mail:
[email protected]
Abstract— A small cost-low civilian UAV (Unmanned Aerial Vehicle - UAV) platform usually requests that all carried components should be light in weight, small in volume, and efficient in energy. A laser diode adopted in LiDAR (Light Detection And Ranging) system is often driven by pulsed voltage, which is several 100 V in voltage, 10-100 A in current, several hundred millisecond in pulse width. A DC-DC converter and a fast switch were often applied by the traditional power supply for driving the LiDAR system. This 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. In this paper, a novel power supply topology, which is based on two coupled coils, pulse generator circuit, and a fast switch, is proposed. The power supply topology has been designed and assembled. After tested, it is confirmed that the proposed power supply is able to generate pulse voltage of 100-300 V, up to 120 A pulse current, 50-200 μs pulse width, and 50 Hz maximum pulse frequency. The specification is sufficient to drive a laser diode used in LiDAR scanning system. This power supply topology gives rid of the DC-DC converter, and is light in weight, small in volume and suitable to be used on a UAV platform. Keywords: UAV, LiDAR, Power Supply Topology
I.
INTRODUCTION
In recent years, a UAV platform becomes more and more interesting and usable for capturing spatial data for a variety of application such as environmental monitoring, resource exploration, LiDAR system, and so on. A small low-cost civilian UAV platform often has limitation on carried components such as volume and weight. This limitation of UAV platform has seriously limited its applications, such as LiDAR onboard UAV, which requires lightness in weight, small in volume, and efficiency in power supply.
A laser diode accompanying with its power supply is an important part of LiDAR system onboard UAV. The energy laser diode on the UAV platform is usually converted by power supply to a special pulsed energy, and then a pulsed laser is emitted from laser diode [1-4]. This 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 for widening LiDAR application onboard. 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. The related work includes Coffey [7] 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. [8], Cheng et al. [9], Zhou et al. [11], Yang et al. [14]. A novel low power supply for DC-coupled 1.25 Gb/s laser diode driver is suggested by Fu et al. [10]. With the MAX797, driver circuit of the high-power laser diode was proposed by Li and Xu [13]. For a pulsed power modulated for high output power for laser fuze was proposed by Guo et al. [14]. The automatic power control of DC-coupled burst-mode laser diode was presented by Zhang et al. [15] and Li et al. [16].
II.
DESIGNED CIRCUIT for LASER DIODE POWER SUPPLY
The laser diode has the following characteristics (see Figure 1): – Peak power >300 W at 30 A driving current and 100
978-1-4577-0969-2/11/$26.00 ©2011 IEEE
– – –
ns pulse width. 905 nm pulsed laser output. Extremely high reliability. Small emitting areas allow ease of lens or fiber coupling.
(a)
(b) Fig. 1 Laser diode (a) and its spectral plot distribution (b) R1
C1
On the basis of the given laser diode, the topology of the laser diode for 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]. The detail is shown in Fig. 2. 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 Q1 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 Q1, 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 (positive terminal in the left, this means the power supply have a negative output); for L1 and L2 are strongly coupled (the coefficient of moment induction is near 1). 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. R2
L2
C2
D1 Q1 B1
R3
L1
C3
GND Fig. 2. Schematic diagram of the power supply for laser diode.
From Fig. 2, it can be noticed that the circuit is simple and realizable, the circuit elements are common. Moreover, the designed power supply will have capability of a great opportunity to meet the demand of the UAV platform. On the basis of the topology above, next step is choice of the parameters of each circuit elements.
III. SPECIFICATIONS OF EACH ELEMENTS AND PRODUCTION 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 3. Instead of traditionally trying every element parameter one by one, a circuit model by PSpice is set up and simultation experiment is conducted. This method is fast and cost efficiency. The simulated model is shown in Fig. 3.
C1
2 1
IC = 28 {Cv al1} 1mH R3 V1 = 0V V1 V2 = 5V PW = 5US PER = 100US
0
510
Q1 BT151
L2
1
100mH
L1
V
C3 {Cv al2} 2
K K1 K_Linear
PARAM ET ERS:
COUPLING = 1 L1 L2
0
Cv al1 = 100U Cv al2 = 100p
Fig. 3. Simulation model of the power supply for laser diode
The omission of some elements in the simulation model in Fig. 3, such as the battery, and R1 in Fig. 2, will not impact the result of the simulation, because the initial state of the simulation is the same as the TTL pulse signal coming state in Fig.2, where the battery and R1 are nonfunctional. The TTL signal is replaced by a pulse generator in the simulation model; the parameter of the pulse generator is shown in Fig. 3. The selected thyristor Q1 is BT151 from Philips. The initial voltage of C1 is 28 V, which is shown in Fig. 3. The
capacitance of C1 and C3 is difficult to choose, we will select the optimal capacitance through simulation result. The inductance of L1 and L2 is 1 mH and 100 mH, respectively, and the two inductors are assumed coupling very well; the coefficient of moment induction is 1. The voltage probe in Fig. 3 is used to obtain the output voltage (see Fig. 3). After completing the model setting up, the capacitance of C3 is fixed to 100 pF, which of C1 is changed from 10 μF to 1000 μF. The result of the simulation is shown in Fig. 4.
Fig.3. Simulation result when C1 changed form 10μF to 1000μF.
From Fig. 4 it is noticed that the capacitance of C1 has little influence to the rising edge of the output voltage, and the rising time is less than 1 μs, and the maximum voltage is about 300 V. The capacitance of C1 affects the falling edge of the output voltage, this because the little capacitance of C1, the less energy of C1 can store, so the faster the energy released. Here we choose a 100 μF C1 to store more energy to drive the laser diode, and also consider the volume and the weight of the power supply. After the capacitance of C1 is set to 100 μF, the capacitance of C3 is changed from 10 pF to 100 pF, to find out the optimal one. The simulation result of this condition is
shown in Fig. 5. From Fig. 5 it is noticed that the capacitance of C3 have little influence to both the rising edge and the output voltage. When capacitance of C3 is 10 pF, the rising edge of the output voltage is steeper, less than 1 μs, so the capacitance of C3 is 10 pF. With the above design, experiments and test, a prototype of power supply is produced, as shown in Fig. 6. 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.
Fig. 5. Simulation result when C3 changed form 10 pF to 1000pF
Fig. 6. A prototype of power supply
IV. CONCLUSION In this paper, a novel power supply topology and simulation experiment for laser diode adopted by LiDAR onboard UAV is presented. The design of this power supply has considered the requirement of LiDAR onboard UAV system, such as light in weight and small in volume. The parameters on the basis of the design supply power topology are specified. The simulated experiment demonstrated that the output voltage of the power supply is meets the demand of driving a laser diode, i.e., pulse voltage of 100-300 V, up to 120 A pulse current, 50-200 μs pulse width, and 50 Hz maximum pulse frequency.
[5] [6] [7] [8]
[9] [10] [11]
ACKNOWLEDGEMENTS This paper is financially supported by GuangXi Governor Foundation. The authors would thank those who gave us their hands in experimental design and technical advice.
[12]
[13]
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