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# help in unregulated 40 power supply

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#### prabid

##### New Member
i got 36 volt transformer 5.5A and bridge 35a and cap 10,000 uf

i need power supply to driver my stepper motor i built the control with l298

the max power to the control is 46 volt

when i connect the transformer with the bridge and with cap i got around 46 volt how ??? i need to get down to 40 or something so the chip don't burn

any help plz????

Because the DC voltage from a fullwave rectifier is equal to the peak voltage of the AC waveform minus the diode drops.
DCVout = (1.414 x VAC) - DiodeDrops
49.5 = (1.414 x 36) - 1.4
Use a transformer with a lower voltage or add a voltage regulator after the filter cap. What is the voltage rating of the stepper motor?

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Yes you need 30V transformer or you could add a regulator but then it would become a regulated supply.

my stepper rate 12volt
and if i add regulator will be difference between the regulator and the unregulated or the result will be the same ???

or the other solution i can change to 30 volt transformer and the problem will be solved

and what is the diffrence to use one filter or 2 filter
i am using now one cap 10.000 uf
so if i put other one in parallel will be the same or the out will change

Why not use a 24VAC transformer, more than enough for a 12V stepper.

The size of filter capacitor depends on the required current and minimum ripple.

I assume you mean 10000µF capacitor, 10µF won't do anything.

Well, if you have a 12V stepper and you don't intend to PWM it, then you should be running it on 12V! Since the l298 drops nominal 3.7V under full load (2A), you need to feed the l298 with around 15.7Vdc to get 12V out for the stepper. A 12VAC transformer with a bridge rectifier and cap would then give you a nominal unregulated 15.6Vdc.
Are you going the PWM the stepper for more torque?

Why would a unregulated supply be used over a regulated one? Cost? Efficiency? If it's efficiency can you bring the input voltage as close to the regulated output voltage as possible to lower the loss?

Mainly cost and efficiency. If you wanted efficiency and regulation, then a switching power supply would be the way to go.

thanx all for helping

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