SoftRock RXTX Ensemble Power Supply 5 Vdc and 12 Vdc

Size: px

Start display at page:

Download "SoftRock RXTX Ensemble Power Supply 5 Vdc and 12 Vdc"

Martha Parrish
5 years ago
Views:

1 SoftRock RXTX Ensemble Reference 1 Purpose and Function The 12 VDC is unregulated and used by the TX Driver/PA section. The 5 VDC is regulated and used by most of the IC s on the board (the USB and Local oscillator being the biggest exceptions) Theory and Design D4 is used to protect the board from being hooked up backwards. If hooked up backwards D4 is reverse biased and little or no current flows into the card. o This Diode is rated for a maximum forward current of 1 amp 2 o A surge current of 30 amps o A maximum reverse voltage of 1000V U9 is a LM7805 5Volt voltage regulator o R52 is not in the reference design provided by National Semiconductor 3 Probably used as a current limiter as I = (12V-5V)/68 = 103 ma which is just above the the Maximum output current of 100 ma 3 R52 and C38 also form a low pass filter 1 Fc 2 RC 4 1 Fc 2 68* 4.7uF Fc 498 Hz which does not seem to be of any value except perhaps if there is a lot of switching noise on the 12 volt supply. o Bulk Capacitors C38 and C40 are both larger than the reference design and should be more than sufficient William R. Robinson Jr. AJ4MC p1of 6

2 SoftRock RXTX Ensemble Calculated The following parameters are for the regulated 5V supply only. No Load Output Voltage 5% of 5 VDC 3 o 5V * 0.05 = 0.25 Volts o Vout_noload = 4.75 to 5.25 Volts Max Load Output Voltage Max load is 100 ma 3 o The worst Rload = 5V/.1 = 50 Ohms Vout_maxload = 4.75 to 5.25 Volts Dropout Voltage Dropout voltage is the minimum Vin-Vout o Any Vin above this voltage should maintain the output volatage o Any Vin below this value will cause Vout to drop also Vdropout = 7.0 V 3 Ripple Rejection -60 dbv at 120 Hz 3 Thermal Shutdown If internal power dissipation becomes too high for the heat sinking provided, the thermal shutdown circuit takes over preventing the IC from overheating. 3 William R. Robinson Jr. AJ4MC p2of 6

3 Simulation NONE SoftRock RXTX Ensemble William R. Robinson Jr. AJ4MC p3of 6

4 Real Circuit SoftRock RXTX Ensemble No Load Output Voltage Vout_noload = 5.08 Volts Max Load Output Voltage With Rload = 50 Ohms for 100 ma Vout_maxload = 4.34 o Note this is below the specification of 5% but when this load is applied the input voltage at pin 1 of the voltage regulator is only 6.18V o This is below the Droput voltage o Also Iin is ( )V/68 = 88ma o This is less than the output current so R52 is limiting the Max Load Vout_maxload when R52 =5.05V Dropout Voltage Dropout voltage is the minimum Vin-Vout o Any Vin above this voltage should maintain the output volatage o Any Vin below this value will cause Vout to drop also Vdropout = 7.0 Volts Ripple Rejection With 110 mvp-p at 120 Hz injected at Pin 1 of the LM7805 there was no noticeable increase in the normal noise of about 20 mvp-p (which seems to be the noise floor of my scope) Vload 20 log( ) dbv = 1.0Volt 5 20mV dbv = 20 log( ) 110mV Ripple Rejection > 14.8 dbv Thermal Shutdown With Rload a dead short the output was 0.09 V and Vin was 2.12 V The device recovered well and never turned hot to the touch William R. Robinson Jr. AJ4MC p4of 6

5 SoftRock RXTX Ensemble Comparison The table below shows good correlation with the documentation See Real circuit for discussion on Max Load Output Voltage and Ripple Rejection Real-Measured Simulation Calculated No Load Output Voltage V 5.08 N/A Max Load Output Voltage V N/A Dropout Voltage V 7.0 N/A 7.0 Ripple Rejection dbv > N/A -62 Thermal Protection Works N/A Works William R. Robinson Jr. AJ4MC p5of 6

6 References SoftRock RXTX Ensemble 1. Robson, Richard R. Sr., WB5RVZ, Ensemble RXTX Project, online, accessed Fairchild Semiconductor, 1N4001-1N4007 General Purpose Rectifiers, online, accessed National Semiconductor, LM78LXX Series 3-Terminal Positive Regulators, online, accessed Paul Horowitz and Winfield Hill, The Art Of Electronics Second Edition (Cambridge University Press), Section 1.19 RC Filters, p UNKNOWN, The ARRL Handbook For Radio Communications, (ARRL 2010) p , (Eq 146) William R. Robinson Jr. AJ4MC p6of 6

SoftRock RXTX Ensemble USB Power Supply USB_5 Vdc and 3.3 Vdc

SoftRock RXTX Ensemble USB Power Supply USB_5 Vdc and 3.3 Vdc Reference 1 Purpose and Function The 5 VDC from the USB port is unregulated but may be regulated by the PC, and used by the ATTiny85 which implements the USB interface in firmware. The 3.3Vdc is regulated