This conversation started as a thermistor question in the parts forum and has morphed into something more: options for a more sophisticated soft start circuit. Since it is now about more than a single part, I thought I'd move it over here to the power supply thread.
With respect to controlling inrush/startup current in a large power amplifier, there seems to be several approaches but no real consensus. Some of you are fine with a properly sized NTC inrush current limiter by itself, others recommend an NTC coupled with a relay (or alternatively, a large resistor and a relay), and finally, a sort of Cadillac solution: the fully implemented soft start circuit on a small PCB. (As a side note, I've seen a popular old Hafler soft start circuit mentioned with a link to the circuit and board, but those old links no longer work.)
I would be fine building a soft start circuit if I knew this was the best and most reliable approach, but I haven’t seen a lot of people supporting the notion so far. Can I ask for thoughts on whether this is worth pursuing? Right now, I'm kind of liking the simplicity of the resistor/relay combination.
With respect to controlling inrush/startup current in a large power amplifier, there seems to be several approaches but no real consensus. Some of you are fine with a properly sized NTC inrush current limiter by itself, others recommend an NTC coupled with a relay (or alternatively, a large resistor and a relay), and finally, a sort of Cadillac solution: the fully implemented soft start circuit on a small PCB. (As a side note, I've seen a popular old Hafler soft start circuit mentioned with a link to the circuit and board, but those old links no longer work.)
I would be fine building a soft start circuit if I knew this was the best and most reliable approach, but I haven’t seen a lot of people supporting the notion so far. Can I ask for thoughts on whether this is worth pursuing? Right now, I'm kind of liking the simplicity of the resistor/relay combination.
Under a coup[le of hundred VA they aren't required.
Over that relay and resistor or relay and NTC thermistor are often used.
I used a phase control circuit to ramp up the mains slowly on my big power amp. It used a very simple PIC micro circuit with a triac.
The PIC ramps up the phase slowly on power up.
Over that relay and resistor or relay and NTC thermistor are often used.
I used a phase control circuit to ramp up the mains slowly on my big power amp. It used a very simple PIC micro circuit with a triac.
The PIC ramps up the phase slowly on power up.
I found the "one size fits all" soft-start solutions to be unsatisfactory and since I like to have options at my disposal I designed a relay board with amplifier soft-start in mind as one of the possible uses. It can be used as a building block to make lots of different kinds of start-up operations. Just add the desired passive components (resistor, NTC thermistor) off-board. More info here:
a versatile delay-on relay board
The relay board allows me to adjust the delay before the contacts of the relay make. I am using a not-very-large 10A relay, however, this is fine as long as you size the soft-start element so that the current is less than that when the relay contacts close. I don't expect any problems. Several boards can be wired in series to trigger one after the other using the "triggered' state of the board that is immediately upstream to begin the timing.
This gives me a lot of flexibility to implement whatever type of soft-start or startup control I want, or to use the board for other applications. The relays that fit this footprint can also be used as speaker relays, so I can use the same board to connect the speakers to the amp after it has settled and the start-up period is over. At the same time I can use an output from the board to disable a mute circuit that uses LED/LDR "Vactrol" type elements so that the audio input is also muted during startup. The possibilities are many
a versatile delay-on relay board
The relay board allows me to adjust the delay before the contacts of the relay make. I am using a not-very-large 10A relay, however, this is fine as long as you size the soft-start element so that the current is less than that when the relay contacts close. I don't expect any problems. Several boards can be wired in series to trigger one after the other using the "triggered' state of the board that is immediately upstream to begin the timing.
This gives me a lot of flexibility to implement whatever type of soft-start or startup control I want, or to use the board for other applications. The relays that fit this footprint can also be used as speaker relays, so I can use the same board to connect the speakers to the amp after it has settled and the start-up period is over. At the same time I can use an output from the board to disable a mute circuit that uses LED/LDR "Vactrol" type elements so that the audio input is also muted during startup. The possibilities are many
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The beauty of triac based solution is there are no relay contacts to burn/weld.
Mine worked up to 3KWatts but needed a heat sink.
Mine worked up to 3KWatts but needed a heat sink.
An externally hosted image should be here but it was not working when we last tested it.
I have seen you mention this several times. Sounds interesting. Have you ever considered putting the work online, e.g. circuit, code, etc? If you already did that can you link to it here?
Here is the pic code.
Code:
[/;INTH0.ASM
;**********
;INTERNAL OSC, INTERNAL MCLR, POWER UP TIMER ON
;
;ON POWER UP WAIT ONE SECOND
;IF MAINS IS THER RAMP UP PHASE ANGLE UNTIL FULLY ON AND KEEP ON UNTIL MAISN FAILS
LIST R=DEC
LIST P=PIC12F508
;INCLUDE REGISTER DEFINITIONS
INCLUDE P12F508.INC
;_MCLRE_ON EQU H'0FFF'
;_MCLRE_OFF EQU H'0FEF'
;_CP_ON EQU H'0FF7'
;_CP_OFF EQU H'0FFF'
;_WDT_ON EQU H'0FFF'
;_WDT_OFF EQU H'0FFB'
;_LP_OSC EQU H'0FFC'
;_XT_OSC EQU H'0FFD'
;_IntRC_OSC EQU H'0FFE'
;_ExtRC_OSC EQU H'0FFF'
__CONFIG _MCLRE_OFF & _WDT_OFF & _CP_OFF & _IntRC_OSC
INCLUDE MACRO.ASM
;ACCESSES REGISTER BANK BIT
#DEFINE RB0 STATUS,5
;
#DEFINE TRIAC GPIO,0
#DEFINE SWITCH GPIO,1 ;
#DEFINE MAINS GPIO,2 ;
#DEFINE LED GPIO,5 ;
STATEA EQU 6
FIRSTA EQU 0
;***********************
FIRSTRAM EQU 7 ;JUST POINTER TO FIRST RAM LOCATION
DEL1 EQU 7
DEL2 EQU 8
WAITTIME EQU 9
LOOPCOUNT EQU 10
MAINSFLAG EQU 11
TIMEOUTL EQU 12
TIMEOUTH EQU 13
LASTMAINS EQU 14
LASTRAM EQU 1FH
;;;;;;;;;;;;;;;;;;;;;
ORG 0
MOVWF OSCCAL
MOVLW FIRSTA
MOVWF GPIO
CLRWDT
MOVLW STATEA
TRIS GPIO
MOVLW 0C0H ;WEAK PULL UPS OFF & WAKE UP ON PIN CHANGE OFF
OPTION
CALL WAIT1SEC ;LET POWER SUPPLY CAP CHARGE UP.
;;;;;;;;;;;;;;;;;;;;;;;
MLOOP BCF LED
BCF TRIAC
CALL WAITMAINSEDGETIMEOUT
BC MLOOP
MOVLW 8
MOVWF WAITTIME
LOOP1
CALL TOGGLELED
MOVLW 25
BTFSC SWITCH
MOVLW 50
MOVWF LOOPCOUNT
LOOP2
MOVF WAITTIME,W
CALL WAITWMS
CALL WAITMAINSEDGETIMEOUTZ ;WAIT MAINS EDGE WITH TIMEOUT WITH TRIAC ON
BC MLOOP
DECFSZ LOOPCOUNT,F
GOTO LOOP2
DECFSZ WAITTIME,F
GOTO LOOP1
RUNLOOP
BCF LED ;KEEP LED OFF TO SAVE POWER
CALL WAITMAINSEDGETIMEOUTZ ;WAIT MAINS EDGE WITH TIMEOUT WITH TRIAC ON
BNC RUNLOOP
GOTO MLOOP
;******************************
WAITMAINSEDGETIMEOUT
CLRF MAINSFLAG
MOVLW 4
BTFSC MAINS
MOVWF MAINSFLAG
;
MOVLW LOW 1071 ;15MS TIMEOUT
MOVWF TIMEOUTL
MOVLW HIGH 1071
MOVWF TIMEOUTH
WM1 MOVF GPIO,W ;14 US LOOP
ANDLW 4
XORWF MAINSFLAG,W
BNZ MAINSCHANGED
DEC16 TIMEOUTL ;(4US)
MOVF TIMEOUTL,W
IORWF TIMEOUTH,W
BNZ WM1
SETC
RETLW 0
MAINSCHANGED
CLRC
RETLW 0
;********************
;WAIT MAINS EDGE WITH TRIAC ON
WAITMAINSEDGETIMEOUTZ
CLRF MAINSFLAG
MOVLW 4
BTFSC MAINS
MOVWF MAINSFLAG
;
MOVLW LOW 1071 ;15MS TIMEOUT
MOVWF TIMEOUTL
MOVLW HIGH 1071
MOVWF TIMEOUTH
BSF TRIAC
WM1Z
MOVF GPIO,W ;14 US
ANDLW 4
XORWF MAINSFLAG,W
BNZ MAINSCHANGEDZ
DEC16 TIMEOUTL ;(4US)
MOVF TIMEOUTL,W
IORWF TIMEOUTH,W
BNZ WM1Z
BCF TRIAC
SETC
RETLW 0
MAINSCHANGEDZ
BCF TRIAC
CLRC
RETLW 0
;********************
WAIT1MS MOVLW 1
GOTO WAITWMS
MS250 MOVLW 250
;ALSO ENTERED HERE
WAITWMS MOVWF DEL1
MS MOVLW 249
MOVWF DEL2
DD NOP
DECFSZ DEL2,F
GOTO DD
DECFSZ DEL1,F
GOTO MS
RETLW 0
;***********************
WAIT1SEC
CALL MS250
CALL MS250
CALL MS250
GOTO MS250
;*************************
TEST
BSF RB0
MOVLW 0
MOVWF GPIO
BCF RB0
TEST1
CLRWDT
MOVLW 0
MOVWF GPIO
MOVLW 255
MOVWF GPIO
GOTO TEST1
;***********************
WAIT100US
MOVLW 25
MOVWF DEL2
DD100 NOP
DECFSZ DEL2,F
GOTO DD100
RETLW 0
;**********************
TOGGLELED BTFSC LED
GOTO WAS1
WAS0 BSF LED
RETLW 0
WAS1 BCF LED
RETLW 0
;**********************
;MACRO.ASM
;*********
;ADD -1
DEC24 MACRO ADDRESS
MOVLW 255
ADDWF ADDRESS,F
SKPNC
INCF ADDRESS+1,F
MOVLW 255
ADDWF ADDRESS+1,F
SKPNC
INCF ADDRESS+2,F
MOVLW 255
ADDWF ADDRESS+2,F
ENDM
DEC16 MACRO ADDRESS
DECF ADDRESS,F
INCFSZ ADDRESS,W
INCF ADDRESS+1,F
DECF ADDRESS+1,F
ENDM
INC16 MACRO ADDRESS
INCFSZ ADDRESS,F
DECF ADDRESS+1,F
INCF ADDRESS+1,F
ENDM
NEG16 MACRO ADDRESS
COMF ADDRESS,F
COMF ADDRESS+1,F
INCFSZ ADDRESS,F
DECF ADDRESS+1,F
INCF ADDRESS+1,F
ENDM
NEG8 MACRO ADDRESS
COMF ADDRESS,F
INCF ADDRESS,F
ENDM
CLR16 MACRO ADDRESS
CLRF ADDRESS
CLRF ADDRESS+1
ENDM
CLR24 MACRO ADDRESS
CLRF ADDRESS
CLRF ADDRESS+1
CLRF ADDRESS+2
ENDM
RRSIGNED MACRO ADDRESS
RLF ADDRESS+1,W
RRF ADDRESS+1,F
RRF ADDRESS,F
ENDM
LOADAD16 MACRO ADDRESS,DATA
MOVLW LOW DATA
MOVWF ADDRESS
MOVLW HIGH DATA
MOVWF ADDRESS+1
ENDM
SHORTLOADAD16 MACRO ADDRESS,DATA
MOVLW DATA ;DONT USE LOW ELSE OVERFLOW ERROR WONT SHOW
MOVWF ADDRESS
CLRF ADDRESS+1
ENDM
SHL16 MACRO ADDRESS
CLRC
RLF ADDRESS,F
RLF ADDRESS+1,F
ENDM
RLC16 MACRO ADDRESS
RLF ADDRESS,F
RLF ADDRESS+1,F
ENDM
CLOCK0 MACRO
BCF SCL
ENDM
CLOCK1 MACRO
BSF SCL
ENDM
DATA1 MACRO
MOVLW DATAPORTSDAIN
TRIS DATAPORT
ENDM
DATA0 MACRO
MOVLW DATAPORTSDAOUT
TRIS DATAPORT
BCF SDA
ENDM
;00
RAMBANK8 MACRO
BCF RAMPAGEBIT0
BCF RAMPAGEBIT1
ENDM
;01
RAMBANK30H MACRO
BSF RAMPAGEBIT0
ENDM
;10
RAMBANK50H MACRO
BSF RAMPAGEBIT1
ENDM
RESETRAMBANK30H MACRO
BCF RAMPAGEBIT0
ENDM
;10
RESETRAMBANK50H MACRO
BCF RAMPAGEBIT1
ENDM
END
CODE]
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Its just PIC assembler.
You will need Microchips MPLAB or MPLAB X to assemble it (free)
I have found that I can use a close rated fuse + soft start with toroid transformers as small as 160VA.
120VA and smaller can usually be started on a T1A fuse and run permanently with this size of fuse.
A 160VA toroid needs a T800mA fuse and may run on a T630mA fuse.
But it will not start repeatedly from cold with this fuse size.
My transformers need at least a T2A fuse to start reliably if I don't fit a soft start.
Typically I use T1A fuse for all my 160VA to 250VA transformers and all fitted with soft start of ~100ohms.
Auxilliary transformers (3VA to 10VA EI) that often operate permanently, even when on standby/off have an F500mA fuse, just in case.
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I use a single soft start for my whole amp which consists of three transformers, 300VA, 160VA and 80VA. They are individually fused after the soft start. Does anyone see any problems with that?
The relay contact will close with a rather low current and even less when you turn off the amp. The welding problem is nonexistent I would say.
I have advised against that.
I recommend an individual current limiting resistor to each transformer and separate bypass contacts to short out those soft start resistors after the time delay.
It just seems wrong to me to have three different inductive loads fed through one resistor.
But maybe I'm being overly cautious.
Probably better to not delay the pre-amp section.To prevent all kinds of transient to pass the final amp with noises and plops in the speakers.
Mona
There's protection circuitry and delay on speakers, and delayed relay on the preamp output too, all a bit over the top really, when I switch on there's a prelude of various clicks!
Hi,
Could we use an AC/DC Converter instead of that transformer and rectifier stage? Like ;
https://uk.farnell.com/tracopower/tmpm-10112/psu-pcb-mount-10w-12v-0-83a/dp/1772176
I never saw these kind of converters which use for soft start product? Is it has any disadvantages ?
Best Regards
Could we use an AC/DC Converter instead of that transformer and rectifier stage? Like ;
https://uk.farnell.com/tracopower/tmpm-10112/psu-pcb-mount-10w-12v-0-83a/dp/1772176
I never saw these kind of converters which use for soft start product? Is it has any disadvantages ?
Best Regards
Attachments
So there is no any problem with this method,great.I can also choise to COSEL;
https://www.digikey.com/products/en?keywords=TUHS10F12
A cap multiplier on the power supply with a slow ramp up is also a nice option. I use this often when a smps has to charge a huge cap bank. Without the cap multiplier, the large in-rush causes the amps to shutdown.
The other benefit is that a relay is not required to prevent speaker turn on thump. The only problem is the dropout voltage. So you have to size transformer higher voltage. Plus is that ripple is removed.
The other benefit is that a relay is not required to prevent speaker turn on thump. The only problem is the dropout voltage. So you have to size transformer higher voltage. Plus is that ripple is removed.
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