K9HZ Full Rig Power Control Unit

Bill Schmidt, K9HZ has  designed a fool-proof control circuit for the uBITx for power control.  This circuit prevents bad things from happening by shutting down the radio before any damage is done. 

It faults on:

  1. reverse voltage
  2. over power
  3. High SWR
  4. High PA Current 
  5. High voltage. 

It provides a visual indication of WHAT fault occurred, and the individual fault LEDs begin to flicker BEFORE the trip so you can fix the problem before you hit a hard trip. 

The fault conditions listed above can be expanded to any number by adding more SCR Trip components (they are set to trip at 1.8V whatever the fault is).

 When initially turned on, the transistorised RS Flipflop circuit comes up in the “Operate” mode.  If a trip occurs, it flips into “FAULT” and shuts down the PA. 

The circuit is reset with the “RESET” button, but ONLY if the fault has been resolved.  Turning the power off and on resets the circuit too.

Bill bread-boarded the circuit last week and has been using it on his radio for a while and found that it works flawlessly (yes transmitting and yanking the coax off the back of the radio shuts down the PA nicely!).  The circuit and a build list can be found in the BITX20 list’s files section.

Parts List for the uBITx Power Control Circuit

Capacitors Value Voltage
C1 10uf 16VDC
C2 0.01uf 50V
C3 0.01uf 50V
C4 0.1uf 50V
C5 0.1uf 50V
C6 0.01uf 50V
C7 0.01uf 50V
C8 0.01uf 50V
C9,C10, C11 0.01uf 50V
Diodes
D1 Green LED
D2 1N4148/ 1N4001
D3 1N4148/ 1N4001
D4 Red LED
D5 1N4148/ 1N4001
D6 12V 0.5W zener 1N759, or 1N5242, or 1N6002
D7 BT149G SCR
D8 BT149G SCR
D9 BT149G SCR
D10 BT149G SCR
D11 1N4148/ 1N4001
D12 1N4148/ 1N4002
D13 1N4148/ 1N4003
D14 1N4148/ 1N4004
D15 Red LED
D16 Red LED
D17 Red LED
D18 Red LED
D19 SB530
Transistors
Q1 2N3904
Q2 2N3904
Q3 2N3904
Q4 2N3904
Q5 2N2222
Resistors Value Watts
R1 1K 0.125
R2 1K 0.125
R3 10K 0.125
R4 10K 0.125
R5 10K 0.125
R6 10K 0.125
R7 10K 0.125
R8 100K 0.125
R9 2.2K 0.125
R10 47K 0.125
R11 1K 0.125
R12 2.2K 0.125
R13 1K 0.125
R14 1K 10-turn POT
R15 10K 10-turn POT
R16 88K 0.125 Can just use a 100K POT set appropriately
R17 12K 0.125 Can just use a 100K POT set appropriately
R18 10K 0.125
R19 100K 0.125
R20 1K 0.125
R21 1K 0.125
R22 1K 0.125
R23 1K 0.125
R24 10K 0.125
R25 10K 0.125
R26 10K 0.125
R27 10K 0.125
R28 62 OHM 2
R29 1K 0.125
R30 1K 10-turn POT 0.125
R31 10K 0.125
R32 100K 0.125
Switch
SPST Momentary contact
Integrated Circuits
U1 LM339 (Make sure to connect Vdd and ground!!!!).
U2 BTS660P
Fuses Value Voltage
F1 1A Poly Fuse 50V
F2 4A Poly Fuse 50V
Conectors
Your choice
Reference

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