Buck Converter

Question 1

What is a SPDT?

Answer 1

A Single Pole Double Throw (SPDT) switch is a switch that only has a single input and can connect to and switch between 2 outputs. It has one input terminal and 2 output terminals.

Question 2

When is the diode and Mosfet on the DC converters?

Answer 2

• The MOSFET is on during the on state.
• The diode freewheels in the off state.

Question 3

What are the assumptions about the buck and boost converter circuits?

Answer 3

1. Capacitance is large enough to negate output voltage ripple. relative to average, or DC, output voltage.
2. L and C have no internal resistance effects that would result in power loss.
3. Power transistor and power diode on-state volt-drops are 0 V.
4. Power transistor and diode switching times are assumed negligible and assumed to produce instantaneous rise and fall transitions.
5. Input voltage is constant.
6. Circuit has been operating for some time and reached a steady state. 7. Output loading constant represented by resistor.

Question 4

What are the implications of the steady-state assumptions?

Answer 4

• For the I_L the sawtooth waveform:
  
  • identical amplitudes.
  • identical shapes

Question 5

Voltage in an inductor

Answer 5

v_L = L di/dt

Question 6

Steps to derive the voltage conversion ratio for a buck inverter.

Answer 6

• Equate the change in inductor current to fall in inductor current.
• Rearrange Equation to find the input voltage.
• V = (T_on/(T_on + T_off))*V_in = Vin*(on time/PWM period) = Vin*D

Question 7

Why is the inductor current triangular?

Answer 7

• The inductor is resistant to change to the change of current.
• In the on-state, the v_L = Vin-V, is positive so the rate of change is constant and positive.
  
  • In the off state, the v_L​ = -v.

Question 8

Buck converter analysis implications

Answer 8

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