The weekly report summarizes the work done on designing a power supply circuit. Key points: - The student designed a charger circuit using an LM317 regulator to charge a 1500mAh 3.7V LI-PO battery within 60 minutes. - Testing showed regulators 7806 and 7805 can generate stable 6V and 5V outputs with input voltages above 7.2V and 7V respectively. - Issues identified were the LM317 running hot during charging and output voltage drops of 7806 below 6V at lower inputs. - Next steps are to improve charging circuit and add an alarm for low 7806 output.

1. [INC 281 MULTIDISCIPLINARY WORKSHOP WEEKLY REPORT] April 20, 2012
Name-Surname Ms. Pornprom Nisaimun
Student ID. 54261518
Group Name Instinct
M 53211801 Kung 54261502
Boss 53211808 Mic 54261507
Engineering Team
Yui 53211835 Arm 54261510
Members
Ball 53211836 Garfield
Top Ice
Product Design P’Jub
Team Members P’Ploy
Weekly Progress
I was Power Supply circuit design responsible. In duration 2 last week ago, I have worked as
follows:
1. Found the information about battery, and I choose to use battery LI-PO
(Lithium-ion Polymer Battery) because it is small (W x L x T = 44 x 67 x 10.7
mm), light, and can distribute current more than its capacity so much. (Page 5)
2. Designed charger circuit by using LM317 because I can vary output voltage
from 1.2 V to 37 V
3. Bought the battery and electronic devices to make an experiment of Power
Supply circuit. (Details of the experiment on page 2 to 4)
4. Design PCB of charger circuit. (Page 4)
5. Approximated of budget (Page 5)
Engineering Analysis
Strong Point
- Both charger circuit, and power supply 5 V and 6 V can operate.
- Size of PCB and battery can put into product.
Week Point
- LM317 in charger circuit is too hot. I think that may be cause of high current to charge
battery.
- IC regulator 7806 cannot retain output voltage when input voltage decrease <7.2 V
Next Week Job
- Design new charger circuit by add current regulator circuit to solve the problem about
temperature.
- Design alarm circuit when output voltage of 7806 less than 6 V.
- Design new PCB of charger circuit.
Department of Control System and Instrumentation Engineering
KING MONGKUT’s UNIVERSITY OF TECHNOLOGY THONBURI

2. [INC 281 MULTIDISCIPLINARY WORKSHOP WEEKLY REPORT] April 20, 2012
The experiment of Power supply circuit
1. Charger circuit test by using 4.2 V, 2 A
Calculation
min
Circuit Test
Battery
Switching
transformer
Fig 1.1 Charger circuit test
Results
V before
30 min 60 min 90 min 120 min 150 min
charged
3.2 V 3.5 V 3.6 V 3.6 V 3.6 V 3.6 V
Summary
Charger circuit by using LM317 with 4.2 V, 2 A can charge battery LI-PO 3.7 V, 1500
mAh in about 60 minutes of time period.
Department of Control System and Instrumentation Engineering
KING MONGKUT’s UNIVERSITY OF TECHNOLOGY THONBURI

3. [INC 281 MULTIDISCIPLINARY WORKSHOP WEEKLY REPORT] April 20, 2012
2. Power supply 5 V and 6 V circuit test
Object
- To ensure that 7.4 V of input voltage can generate output voltage 6 V and 5 V by
IC regulator 7806 and 7805
- To find critical input voltage that the IC regulator cannot retain output voltage to
6 V and 5 V
Test circuit
Fig 2 Power supply 5 V and 6 V circuit by using LM317 to generate voltage apply to
input of 7806 and 7805
Results
Vin Vout 7806 (J2) Vout 7805 (J3)
6.8 V 5.6 V 5.15 V
7.0 V 5.8 V 5.15 V
7.2 V 6V 5.15 V
7.4 V 6.2 V 5.15 V
7.6 V 6.4 V 5.15 V
7.8 V 6.4 V 5.2 V
Summary
IC regulator 7805 can retains voltage output well while IC regulator 7806 will retain
certainly output voltage at input voltage >=7.2 V. So if we use two series of 3.7 V to make
voltage 7.4 V and apply to input of IC regulator, we can generate output voltage 6 V and 5 V.
However, we have to ensure that Gas sensor (use supply voltage 6 V) can operate with this
condition.
Department of Control System and Instrumentation Engineering
KING MONGKUT’s UNIVERSITY OF TECHNOLOGY THONBURI

4. [INC 281 MULTIDISCIPLINARY WORKSHOP WEEKLY REPORT] April 20, 2012
LI-PO
7.4 V, 1500 mAh
(3.7 V x 2 )
Fig 3 As-built circuit
3. The size of PCB charger circuit
24 mm
20 mm
46 mm
Department of Control System and Instrumentation Engineering
KING MONGKUT’s UNIVERSITY OF TECHNOLOGY THONBURI

5. [INC 281 MULTIDISCIPLINARY WORKSHOP WEEKLY REPORT] April 20, 2012
4. The approximation of budget
Price/each Total
No. Details Amount Shop
Baht Baht
1. Switching transformer 12 VDC, 2 A 150 1 140 0-2222-
2. DC Jack 10 1 10 4990, 0-2222-8476
3. Battery LI-PO 3.7 V, 1500 mAh 150 2 300 3D 0-2221-5768,
08-9230-7894
4. C 0.1 uF/50 V 1.10 3 3.3
5. C 10 uF/50 V 1.10 1 1.10
6. C 1 uF/50 V 1.10 1 1.10
7. C 0.33 uF/50V 1.10 1 1.10
8. LM317TG 9 1 9
9. R 240 Ω ¼ W 0.12 1 0.12
10. POT 5 kΩ 25 turns 25 1 25 (NPE) 0-2225-
11. MC7805 6.50 1 6.50 0094, 0-2225-2528
12. L7806 7.20 1 7.20
13. Connector Male WKH-N02BIT-L 0.75 4 3
14. Connector Female WKH-C02B 1 4 4
15. PCB Tab Vertical 1 2 2
16. Spring 20 2 40
Total budget 553.42
*Note As the approximation dose not add VAT.
5. The comparison to LI-PO Battery table
(mm) Price
Capacity Voltage Weight Datasheet
W L T (Baht)
1350 mAh 7.4 V 35 67 14 80 g 618 with
1350 mAh 7.4 V 35 69 21.7 89 g 390 without
1500 mAh 7.4 V 44 67 10.7 - 300 without
Department of Control System and Instrumentation Engineering
KING MONGKUT’s UNIVERSITY OF TECHNOLOGY THONBURI