smokyLED Posted December 11, 2005 Report Share Posted December 11, 2005 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. PARTSTF1 230/24V 100VA transformerF1 1A fuseF2 6A fuseSW1 on-off 250Vac SW2 on-off switchTS1 240V on-off switchM1 Panel meter 5Adc M2 Panel meter 30Vdc IC1 LM 324 quad opampIC2 7812 jänniteregulaattori +12V D1 1N4004D2 - D6 1N4148 tai 1N4448 tai vastaava D7 1N4004 D8 Zener diode 6V 1,3W D9 LED D10 LED D11 LED TY1 TIC47 thyristorTR1 2N3055 transistorTR2 BD237 transistorTR3 - 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 1kohmR24 0,3ohm 5W The original design is from http://koti.mbnet.fi/~huhtama/ele/index.php?si=kyt01.sis&pa=j Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 11, 2005 Report Share Posted December 11, 2005 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. Quote Link to comment Share on other sites More sharing options...
smokyLED Posted December 11, 2005 Author Report Share Posted December 11, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 11, 2005 Report Share Posted December 11, 2005 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. Quote Link to comment Share on other sites More sharing options...
smokyLED Posted December 11, 2005 Author Report Share Posted December 11, 2005 pin 4 and 11 is connected. i get full rail voltage at pin 1, and there is a voltage on pin 14 Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 11, 2005 Report Share Posted December 11, 2005 Pin 7 drives R11 and pin 8 drives R10. Maybe those resistors have a value much less than 10 thousand ohms. Quote Link to comment Share on other sites More sharing options...
smokyLED Posted December 12, 2005 Author Report Share Posted December 12, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 12, 2005 Report Share Posted December 12, 2005 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. Quote Link to comment Share on other sites More sharing options...
smokyLED Posted December 13, 2005 Author Report Share Posted December 13, 2005 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 Quote Link to comment Share on other sites More sharing options...
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