Buck Chopper
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Buck chopper
Operation :- Whenever the mosfet Q1 is turned on the input is connected to the output via the inductor and whenever the mosfet Q1 is turned off, energy stored in inductor L circulates through the diode D1 to the output.
The output voltage is proportional to the duty cycle Vo = D * Vin
Tips on Buck chopper:
The losses on the buck chopper depends on the mosfet conduction, switching, Coss loss, Input gate charge loss due to Ciss. Inductor loss consists of copper loss and core loss. The copper loss depends on the dc loss, and the ac loss. Dc copper loss is due to the DC current flowing through the inductor. AC copper loss is mainly due to skin effect, and proximity loss loss. The output capacitor has power loss due to ESR. When the output voltage is too low in terms of 1.2Volts its advisable to replace the diode D1 with a mosfet. By changing the diode to a mosfet you gain higher efficiency because the voltage drop of the mosfet is much lower than the voltage drop of the diode. However it comes with complexity such as during turn on and tun off the mosfet needs to be turned off as well as whenever the output current is low.
Component selection :
Mosfets :- Every manufacturer has its own method of fabricating mosfet. Some mosfet which has lowest Rds suffers with high Ciss and Coss. Some mosfets have higher Rds on but has lower Ciss, Coss and hence can be used for high frequency application. Select the mosfet depending on the losses. Preferred Vendor IR, Vishay, Fairchild, Infinion etc..
Output inductor :- The output inductor has a flux swing proportional to the Ac ripple current. Powdered iron core is the best material. Preferred Vendor :- Micrometals
Output capacitor :- Calculate the ripple current through the capacitor and multiply with a derating factor. Preferred Vendor : Nichicon, Jamicon, united chemicon,
Pulse Transformer:- To turn on and off the top FET Preferred Vendor :- Pulse Engineering, Preferred core :- Mag-inc, Ferroxcube, TDK.
Application notes:
For more details please refer to the application note about buck chopper. (It would be posted soon as a pdf).
(If you are looking for any help, technical difficulties on your project please consider J Thomas for consultancy/Independent contractor.)
J Thomas
josethom@gmail.com
jthomas@powerelectronicsconsultant.com
Ph :- 714 7263837
back to main>
Operation :- Whenever the mosfet Q1 is turned on the input is connected to the output via the inductor and whenever the mosfet Q1 is turned off, energy stored in inductor L circulates through the diode D1 to the output.
The output voltage is proportional to the duty cycle Vo = D * Vin
Tips on Buck chopper:
The losses on the buck chopper depends on the mosfet conduction, switching, Coss loss, Input gate charge loss due to Ciss. Inductor loss consists of copper loss and core loss. The copper loss depends on the dc loss, and the ac loss. Dc copper loss is due to the DC current flowing through the inductor. AC copper loss is mainly due to skin effect, and proximity loss loss. The output capacitor has power loss due to ESR. When the output voltage is too low in terms of 1.2Volts its advisable to replace the diode D1 with a mosfet. By changing the diode to a mosfet you gain higher efficiency because the voltage drop of the mosfet is much lower than the voltage drop of the diode. However it comes with complexity such as during turn on and tun off the mosfet needs to be turned off as well as whenever the output current is low.
Component selection :
Mosfets :- Every manufacturer has its own method of fabricating mosfet. Some mosfet which has lowest Rds suffers with high Ciss and Coss. Some mosfets have higher Rds on but has lower Ciss, Coss and hence can be used for high frequency application. Select the mosfet depending on the losses. Preferred Vendor IR, Vishay, Fairchild, Infinion etc..
Output inductor :- The output inductor has a flux swing proportional to the Ac ripple current. Powdered iron core is the best material. Preferred Vendor :- Micrometals
Output capacitor :- Calculate the ripple current through the capacitor and multiply with a derating factor. Preferred Vendor : Nichicon, Jamicon, united chemicon,
Pulse Transformer:- To turn on and off the top FET Preferred Vendor :- Pulse Engineering, Preferred core :- Mag-inc, Ferroxcube, TDK.
Application notes:
For more details please refer to the application note about buck chopper. (It would be posted soon as a pdf).
(If you are looking for any help, technical difficulties on your project please consider J Thomas for consultancy/Independent contractor.)
J Thomas
josethom@gmail.com
jthomas@powerelectronicsconsultant.com
Ph :- 714 7263837
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