0-24V 4A bench supply

[smokyLED]

I have built this circuit, and i can adjust the voltage and current correctly using the pots. However the current limiting and temperature cutout doesn't seem to work.

I am getting no voltage at pins 7 or 8 of the LM324.

PARTS

TF1 230/24V 100VA transformer
F1 1A fuse
F2 6A fuse
SW1 on-off 250Vac
SW2 on-off switch
TS1 240V on-off switch
M1 Panel meter 5Adc
M2 Panel meter 30Vdc
IC1 LM 324 quad opamp
IC2 7812 jänniteregulaattori +12V
D1 1N4004
D2 - D6 1N4148 tai 1N4448 tai vastaava
D7 1N4004
D8 Zener diode 6V 1,3W
D9 LED 
D10 LED
D11 LED 
TY1 TIC47 thyristor
TR1 2N3055 transistor
TR2 BD237 transistor
TR3 - TR4 BC547 transistorC1 Elektroi 4700uF 40V
C2 Polyester 220nF 63V
C3 Elektro 100uF 40V
C4 Polyester 100nF 63V
R1 - R2 1kohm 0,25W
R3 - R4 10kohm 0,25W
R5 3,3kohm 0,25W
R6 1kohm 0,25W
R7 33kohm 0,25W
R8 10kohm 0,25W
R9 470kohm 0,25W
R10 - R11 10kohm 0,25W
R12 33kohm 0,25W
R13 10kohm 0,25W
R14 - R15 10kohm 0,25W
R16 - R18 1,5kohm 0,5W (or 2 series 820ohm 0,25W)
R19 Potentiometer 47kohm LIN
R20 Potentiometer 1kohm LIN
R21 Trimmeri 10kohm
R22 Trimmeri 1kohm 
R23 NTC 1kohm
R24 0,3ohm 5W

The original design is from http://koti.mbnet.fi/~huhtama/ele/index.php?si=kyt01.sis&pa=j

 

[audioguru2]

Hi Smokey,
Pin 7 should go high when the voltage at the slider of R22 that is caused by output current, exceeds the voltage at the slider of R20 its reference voltage.

Pin 8 should go high when the voltage at pin 9 drops a little lower when the thermistor is hot, than the voltage at the slider of R21 its reference voltage.

 

[smokyLED]

yep, just what i thought. but it still doesn't work. i've triple checked the wiring and components and tried different LM324. still doesn't go high when there is a difference.

 

[audioguru2]

yep, just what i thought. but it still doesn't work. i've triple checked the wiring and components and tried different LM324. still doesn't go high when there is a difference.

Then its pin 4 doesn't have a supply voltage connected.
Pin 7 should go high when there is 10mV or less difference in voltage at its inputs due to its input offset voltage, then amplifies it a few hundred-thousand times. Pin 8 needs a little more voltage difference due to the hysteresis provided by the positive feedback.

 

[smokyLED]

pin 4 and 11 is connected. i get full rail voltage at pin 1, and  there is a voltage on pin 14

 

[audioguru2]

Pin 7 drives R11 and pin 8 drives R10. Maybe those resistors have a value much less than 10 thousand ohms.

 

[smokyLED]

replaced the 10k resistors and it works now.

what is the point of having TY1 and SW2, when TR4 already provides current limiting by shorting IC2's supply to ground. There doesn't seem to be any short circuit protection in this circuit... because when i short the output, current limiting kicks in, but i can hear buzzing.

 

[audioguru2]

replaced the 10k resistors and it works now.

Good! ;D Was the orange band on the resistors actually gold? (1 ohm)

what is the point of having TY1 and SW2, when TR4 already provides current limiting by shorting IC2's supply to ground. There doesn't seem to be any short circuit protection in this circuit... because when i short the output, current limiting kicks in, but i can hear buzzing.

I think the switch and SCR would give an indication and protection if the load has an intermittent short.
The buzzing is probably the transformer straining at full current.

 

[smokyLED]

nah, the bands are correct, but the resistance was 2k ohm, even though it's a 1% tolerance resistor.... i'll remember to check resistors with a meter in future, instead of relying on the markings