Transcript Linear Power Supply Outline • Linear Power Supply – Poor man’s cell phone charger – Small signal resistance • Adjustable power supply • Rectifier Circuit –

Linear Power Supply
Outline
• Linear Power Supply
– Poor man’s cell phone charger
– Small signal resistance
• Adjustable power supply
• Rectifier Circuit
– Half-wave rectifier circuit
– Full-wave rectifier circuit
– Full-wave rectifier circuit as a Frequency
mixer
• Filter Circuit
Outline
• Large-Signal and Small-Signal
Operation
• Application of Diodes (Up to 3.5.1)
How does a small increase in Vad affect Vout?
Drop in Output Voltage
(Slope)
Small Signal Resistance
Small Signal Resistance: ID/VT
I-V Characteristic of a 1n4001
Diode
Export I-V Data to a Table
Export Table
Small Signal Resistance
VF (V)
IF (Computed)
0.748
0.740
67.57 mA
57.89 mA
Dynamic Resistance from the measurement:
(0.748-0.740)/(67.57 mA-57.89 mA)= 0.826 Ohms
Using Small Signal Model in a
Small Signal Calculation
Small Signal Model of Adaptor
Change in Vad
How should a load be
modeled?
A laptop consumes an average power of 25 W with a supply
voltage of 3.3 V. Determine the average current drawn from
the batteries or the adaptor.
P=VI
I= 7.56 A
If the laptop is modeled by a resistor, then RL is 0.436 Ohms.
You Can’t Power a Laptop
with a Circuit Like this!
How should a Cellphone load
be modeled?
A cellphone consumes an average power of 100 mW with a supply
voltage of 2.4 V. Determine the average current drawn from
the batteries or the adaptor.
P=VI
I= 41.6 mA
If the cellphone is modeled by a resistor, then RL is 79 Ohms.
Use a 79 Ohm Resistor to
Model a Cell Phone Load
Dual-Output Adjustable
Linear Regulated Power
Supply
Block Diagram
Simple Description
• Transformer: “Downconvert” the AC
line voltage to a smaller peak voltage
Vm, usually about 2-3 Volts larger than
the ultimately desired DC output.
• Diode Rectifier Circuit: produce a
waveform with large DC component.
• Filter: smooth out the rectified sinusoid.
• Regulator: eliminate residual ripple
c03f27
Half-Wave Rectifier
Voltage offset
Diode is off for
Vin < VD,on
Assume constant voltage model for diodes
On for Vin less than –VD,on
An AC-DC Converter Circuit
Ideal Diode Model
An AC-DC Converter Circuit
Constant Voltage Diode Model
Issue: It remains to be seen whether it can
provide a current to a load
How should a load be
modeled?
A laptop consumes an average power of 25 W with a supply
voltage of 3.3 V. Determine the average current drawn from
the batteries or the adaptor.
P=VI
I= 7.56 A
If the laptop is modeled by a resistor, then RL is 0.436 Ohms.
Rectifier Driving a Resistive Load
The diode is
turned on again
ripples
Vin begins to fall after t1 because RL provides
a discharge path for C1.
C1 must be sufficient large so that the current
drawn by RL does not reduce Vout significantly.
C1 is called smoothing capacitor
Magnitude of the Ripple
Tin
(Vp-VD,on)/RL is the current
discharged through RL
(basic form of this equation:
Q=CV)
The Maximum Forward Bias Current
Maximum Forward Current Occurs at the point
when the diode turns on (t1)
1. C1dVout/dt is maximum
2. The current supplied to RL is (Vp-VD,on)/RL
Screen Shots
Smoothed Capacitor