### Chopper1

• 1. CHOPPERS  Transfer power from DC circuit to another DC circuit.  Converts fixed voltage to variable voltage.
• 2. Application of Chopper 1.Speed control of DC Motor. 2.Positional control in robotics. 3.Regulated power supply (SMPS) 4.Input to Inverter. 5.Solar Power Converter.
• 3. Step Down Chopper CH: - fully controlled switch Operation: - Periodic Time period: - T Duty cycle: - Ton/T Ton = DT CH: - ON Vo=Vs CH: - OFF Io=0/Vo=0 t t t
• 4. Buck Converter S1 :- Fully Controlled Switch -MOSFET(high frequency)/IGBT/SCR+Commutation Circuit S2:- Uncontrolled Switch :- provides free wheeling action (due to L) DC Motor load -Step down chopper with a freewheeling diode.
• 5. Buck Converter SW:-ON (0<t<DT) Vo = Vs Vs = 𝑖𝑅 + 𝐿 𝑑𝑖 𝑑𝑡 + 𝐸 L :- charging SW :- OFF (DT<t<T) 0 = 𝑖𝑅 + 𝐿 𝑑𝑖 𝑑𝑡 + 𝐸 L:- discharging
• 6. 𝐼𝑚𝑎𝑥 = 𝑉𝑠 𝑅 1−𝑒 −𝑇𝑜𝑛 𝜏 1−𝑒 −𝑇 𝜏 − 𝐸 𝑅 𝛕 = time constant = L/R 𝐼𝑚𝑖𝑛 = 𝑉𝑠 𝑅 𝑒 𝑇𝑜𝑛 𝜏 −1 𝑒 𝑇 𝜏−1 − 𝐸 𝑅 T = time period (Valid when 𝛕 ≤ T) ∆I = ripple in inductor current = Imax – Imin Ripple must be as low as possible Maximum ripple in IL occurs if D = 0.5 (Buck Converter) ∆I = Vs/4fL (assume 𝛕>>T)To reduce the ripple, f and L must be high∆𝐼 = 𝑉𝑠 𝑅 1−𝑒 −𝑇𝑜𝑛 𝜏 1−𝑒 −𝑇 𝜏 − 𝑒 𝑇𝑜𝑛 𝜏 −1 𝑒 𝑇 𝜏−1 = 𝑉𝑠 𝑅 (1−𝑒 −𝑇𝑜𝑛 𝜏 ) (1−𝑒 −𝑇 𝜏 ) − 𝑒 −𝑇 𝜏 (𝑒 𝑇𝑜𝑛 𝜏 −1) (1−𝑒 −𝑇 𝜏 ) = 𝑉𝑠 𝑅 1−𝑒 −𝑇𝑜𝑛 𝜏 1−𝑒 −𝑇 𝜏 (1 − 𝑒 −𝑇 𝜏 ∗ 𝑒 𝑇𝑜𝑛 𝜏 ) = 𝑉𝑠 𝑅 1−𝑒 −𝑇𝑜𝑛 𝜏 1−𝑒 −𝑇 𝜏 (1 − 𝑒 −𝑇𝑜𝑓𝑓 𝜏 )
• 7. Discontinuous Conduction • Current can become 0 for finite duration of time. • Boundary :- When current IL=0 only for an instant of time. • For boundary :- Imin =0 • 𝑉𝑠 𝑅 𝑒 𝑇𝑜𝑛 𝜏 −1 𝑒 𝑇 𝜏 −1 = E/R • 𝑒 𝑇𝑜𝑛 𝜏 − 1 = 𝐸 𝑉𝑠 𝑒 𝑇 𝜏 − 1 • 𝑇𝑜𝑛 = 𝜏𝑙𝑛 1 + 𝐸 𝑉𝑠 𝑒 𝑇 𝜏 − 1
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