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Step Down Power supply

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shaljdav

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Hi everyone, I am designing Power supply, using LTC7138 Step-down regulator. Input voltage is equal 130V and the output should be also 130V output voltage with 400mA maximum output current. After designing and testing the circuit, unlikely for me, the results were not satisfied me. When the RLOAD = 400 ohm, the output voltage is equal 110V instead of 130V and hence the output current is equal 275mA. With increasing RLOAD the Output voltage also increases, especially when RLOAD is equal 1.3k, output voltage is equal 125V (output current = 125V/1.3k = 95mA). I don’t think there is exciting internal resistance. So I need an answer please.

Here below you can find the circuit which I’ve tested.
kk.png
 

Hi,

Since it is a step DOWN supply ... the output voltage will be less than the input voltage.

The controller is able to go to 100% duty cycle, then the voltage drop is only the drop of the internal switch and the DC resistance of the external inductance.
* The switch ON resistance is about 1.8 Ohms.
* What is the coil resistance?
And due to your 130V/130V configuration it is likely that the duty cycle isn´t 100%.

I don´t think it makes sense to build a 130V in --> 130V out supply. What is it good for?

Klaus
 

Hi , thank you for your response.
LTC7138 regulator's output range is about from 0,8V to Vin (130V in this case)
This LTC7138 regulator is adjustable. The final purpose is to get Programmable Power Supply with the output voltage range from 0,8V to 125V, which we can obtain by changing the values of R2 or R3 resistors. Now I am on my first stages, and I just only want to make sure that my Power supply will produce the maximum output power (130V 400mA).
The DC resistance of the external inductance is about milliohms. From the measurement results, iT looks like 70 ohm internal resistance exciting in the circuit
 

Hi,

LTC7138 regulator's output range is about from 0,8V to Vin (130V in this case)
Vin is a theoretical limit here. Only with 100% duty cycle and no load current.

If you want 125V output, then ensure at least 130V input voltage. In any case. No drop below 130V even with full load.
I´d go for an even higher margin.

Klaus
 

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