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Peter Miles
Northam, Western Australia
QRZ Page: VK6YSF
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REGULATOR 12VDC TO 5.0VDC 2.0A
12V
to 5.0V DC/DC 2.0 Amp voltage regulator. December 2024.
A
5.0VDC supply was required to power radio receiving equipment from a 12VDC
main supply. A more efficient switch mode power supply was rejected as
there was concern that this type of equipment may generate RF noise,
therefore an older regulator type supply was chosen.
The TIP2955
transistor provides the necessary current when the load requires is more than 1A, while the 7505 ensures the voltage stays constant at 5V.
The 7505 continues to regulate the voltage to 5V, while the TIP2955 handles the increased load, ensuring the output remains stable at 5V and can supply up to
approximately 2A.
Fig
1 Schematic diagram
Fig
2 Component layout with PCB strips glued to a negative/ground PCB
square sheet.
Photo
1 Component layout with in heavy aluminium enclosure and heaver
aluminium back mounting plate to act as a heat sink.
Since the circuit uses linear regulation, it is less efficient compared to switching regulators, especially at higher currents. The power dissipation in the form of heat can be significant, which
will require a large heat-sink for the TIP2955 and 7505. The
transistor and regulator chip are fixed to the heat-sink with heat
conducting grease to aid the heat transfer.
Testing
results
| Load
Amps |
Input
Voltage |
Out
put Voltage |
Temperature
TIP2955 |
| 0 |
13.58v |
5.06v |
Ambient,
21.0°C |
| 2.07A |
12.8v |
5.06v |
86°C.
Device rated at 130°C |
Fig
3 Load test
Power
Output
Power (5.0v): 10.4W
Input
Power (12.8v: 26.5w
Efficiency:
39%
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| TIP2955
Pin-outs
The TIP2955 is a PNP power transistor commonly used for high-power applications.
Its key specifications are as follows:
Electrical Characteristics
Transistor Type: PNP
Collector-Emitter Voltage (Vceo): -60V (maximum)
Collector-Base Voltage (Vcbo): -100V (maximum)
Emitter-Base Voltage (Vebo): -5V (maximum)
Collector Current (Ic): -15A (maximum continuous)
Peak Collector Current (Icm): -25A (non-repetitive)
Thermal and Power Characteristics
Total Power Dissipation (Ptot): 90W (with proper heatsinking at Tc = 25°C)
Junction-to-Case Thermal Resistance (Rθjc): Typically 1.39°C/W
Operating Junction Temperature (Tj): -65°C to +150°C
Gain Characteristics
DC Current Gain (hFE):
Typically 20–70 (at Ic = -4A, Vce = -4V)
Minimum of 15 at higher currents (Ic = -10A)
Switching Characteristics
Transition Frequency (fT): 3 MHz (typical)
Collector Capacitance (Cc): Approximately 300 pF (at Vcb = -10V, f = 1 MHz) |
7805
Regulator pin-outs
The 7809 is a commonly used linear voltage regulator in the 78xx series. Its key specifications are as follows:
Input and Output Characteristics
Output Voltage: 9V (regulated)
Input Voltage Range: Typically 11.5V to 35V (depends on the manufacturer, but at least 2V higher than the output voltage for proper regulation).
Output Current: Up to 1A (with proper heat sinking).
Line Regulation: Typically 0.01%/V.
Load Regulation: Typically 50mV for 0 to 1A load changes.
Thermal Characteristics
Power Dissipation: Limited by the package and heatsinking, typically 15W with proper heat dissipation.
Thermal Shutdown: Yes, integrated protection against overheating.
Operating Junction Temperature: Usually -40°C to +125°C.
Protection Features
Short-Circuit Protection: Yes, internal limiting of current.
Overload Protection: Thermal and current limiting.
Reverse Polarity Protection: Some manufacturers may include limited protection against reverse polarity at the input.
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Fig 4 TIP2955 transistor and
7805 regulator pin-outs and general specifications.
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OF PAGE
Page initiated 01
December, 2024
Page
last revised 05 May, 2025
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Space Weather
https://www.swpc.noaa.gov/
Notice Board
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VK6YSF JS8Call,
FSQ and
Olivia 8/250 operations.
Current
activity is generally, however not restricted to operations with
JS8Call, FSQ and Olivia 8/250 on the 20m and 40m band.
Proposed
band and mode activity
is often communicated on HamSpots: https://hamspots.net/js8/
or my profile on
X: https://x.com/vk6ysf97230
.
Feel free to contact
me to discuss or arrange a schedule for a contact.
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VK6MJM LF (136 kHz) and MF (474
kHz) Beacon
VK6MJM is a LF/MF station
located in Manjimup, Western Australia.
Mode: Mode: FST4W 300 (Similar to WSPR)
Station details were presented by
Peter Hall (VK6HP) at PerthTech 2024.Presentation PDF: Peter
Hall VK6HP at PerthTech
QRZ Page: VK6MJM
on QRZ.com
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