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SG3524

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Lumpin

New Member
Hi there!

Does anyone here familiar with the PWM IC SG3524? My question here is how to adjust the duty cycle. Which pins should i alter if i want to vary the duty cycle? My operating voltage will be 12V.

Any relevant schematic will be much helpful.

Thanks in advance.
 

Scubasteve

New Member
Hey,

I believe that the PWM duty cycle is a function of the feedback voltage, but I am not sure. Play around with pin 1 and 2 of the device and this should vary your duty cycle, these are the inverting/non-inverting inputs of the error amplifier.

Steve

What are you using this for? may i ask..
 

Chippie

Member
As Scubasteve says, the duty cycle is a functional variable dircetly influnced by the feedback voltage obtained from sampling the output voltage....As the o/p voltage falls due to increased loading the duty cycle decreases, so the on time of the switching elements is increased,increasing the power transfer to the secondary side of the supply........All you can influence is the switching frequency, by changing the values of the resistor and capacitor on pins 6/7 respectively. Pins 4 and 5 will also impact on the duty cycle, these are used for curent sensing to detect overload, the switching action wil revert to a minimum duty cycle.........


HTH Chip
 

Lumpin

New Member
Thanks for your fast reply steve and chippie :)

Actually, i want to learn to design a dc motor speed controller using this SG3524 IC. A simple one. So far, i only found one circuit at https://www.4qdtec.com/images/pwm.gif but it's way too complicated for me. (I wonder why i can't attach the schematic here). Moreover, the datasheet for this IC lacks of informations for a beginners like me.

From what i see from that circuit, the input signal is fed through pin 16, pin 2 and to the ground. Pin 1 is connected to pin 9 (and ground) via a 100K resistor. The datasheet for the SG3524 says that the pin 16 is the 5 V reference. So, does this means that the duty cycle is varied by altering the voltage between pin 16 and pin 2? not pin 1 and pin 2?

I hope you don't mind (if you have one) to share any simple speed controller circuit using this IC.

Thanks in advance.

Har
 

Chippie

Member
I'll take a stab and say the ref voltage is applied across an external pot whose slider is connected to pin 2 via the 10k resistor......'fraid I dont have any other schematics...... :(
 

Lumpin

New Member
Chippie, do you mean that the duty cycle is varied by adjusting the Vref and also voltage to pin 2? From what i get, if we slide the pot so that the voltage from vref to ground increase, the voltage at pin 2 to ground will decrease, and vice versa. This will simply adjust the duty cycle, am i right? Please correct me if i'm wrong.

I've seen a circuit which didn't use the pin 4 and 5 of this chip, however that circuit is intended for use with car audio amplifier. Is it ok if i simply ground these pins for motor speed controller?

About pin 6 and 7, from what i understand is that these pins are used as the switching frequency. From that circuit, it is using 4.7K resistor and 10nF cap. Using the equation 1/(Rt x Ct) yields the frequency as 21.3kHz. Divide it by 2 yields the frequency as 10.65 kHz (correct me if i'm wrong). The question is why the circuit use this frequency (10.65 kHz) ? Does it has anything to do with the remote control frequency or it's just depends on the designer of what frequency he want to use?
 

Scubasteve

New Member
I do not recommend using this IC for a motor speed control, its use is best for switching power supplies.. This IC cannot ever reach 100% PWM, just a max of 90%, which isn't great. This means, whatever your motor is, you will only be able to use 90% of its power..

I am sure there are more PWM ICs out there... try www.allegromicro.com

Steve
 

causalitist

New Member
**broken link removed**

i used this.. its great..
it goes up to 98% pwm.. its fine.

i really like the ramp speed adjustment.
that 4qd circuit is insane.. most of it doesnt look to bad, but anyone who knows there stuff will tell you those 4qd guys are god.

even this circuit is more complicated than needed... you could eliminate the transistor/ramp speed stuff completely.. forget that opamp on the bottom as well until later...

all you need is a voltage divider from the REF pin to the non-inv input pin (2??) and to ground.. use a pot, with wiper to the chip non inv... one side to ground, one side to Vref pin...

experiment with reistor values between pot and ground, and pot anf vref.. to get the response you want..

basically, 0-5v to the non-inv pin controls duty cycle... the rest is easy.. pin 1 to 9 directly.. pin 8 to ground, (forget soft start).. both pins 4 and 5 to ground until later when you worry about current limiting.
 
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