Switch Mode Power Supply
(SMPS)
Troubleshooting
Why?
• Starting with the 11 product line, Switch
Mode Power Supplies (SMPS) are used in all of
Denon and Marantz AVR’s.
Outline
•
•
•
•
Introduction
Power Supply Review
Switch Mode Power Supply (SMPS) Operation
Troubleshooting
What is a Power Supply?
A Power Supply Converts Electrical Power
A power supply converts available electrical energy to a form
required by various circuits used within an electrical system. The
most common power supply used in Audio Equipment converts AC to
DC, but power supplies can also convert DC to DC, or DC to AC.
Common Power Supply Components
Power Supply Components
1.
2.
3.
Conversion (mandatory)
Isolation (Optional)
Regulation (Optional)
Linear Regulation Power Supply Components
Isolation
conversion
Regulation
What is a SMPS?
• A Switch‐Mode Power Supply uses a switch to
regulate output voltage
Switch
How Does A Switch Regulate DC?
1.
2.
3.
DC Output Controlled By Switch On Time
SMPS Components
Isolation
conversion
Hot Ground
Cold Ground
Regulation
Caution ‐‐‐ An ISOLATION TRANSFORMER must be used
when connecting test equipment to the HOT GROUND
side of the power supply.
Why Use a SMPS?
Transformer
Regulator
Greater Efficiency
1.
2.
In a Series Regulated power
supply, the regulator operates in
the linear region and is always
conducting
In a SMPS, the switch is either
full on or off. This reduces heat
and improves efficiency
Capacitor
Linear Regulated Power Supply
Smaller Components
1.
2.
Capacitors
Transformers
Switch/Regulator
On/Off switching Simplified
Transformer
Capacitor
SMPS
Why Use a SMPS?
1.
Smaller Components
1. Capacitors
2. Transformers
SMPS Advantage – Simplified Standby Supply Over Units with Linear Supplies
AVR3808CI Standby Supply Includes:
AVR3808CI Standby Supply Includes:
1. 2 Standby and 1 Run 5VDC Source
2. 2 Relays to control on/off switching
3. 5 VDC Switching Circuit
4. 2 on/off Control Lines from CPU
AVR3808CI Standby Power Supply Block Diagram
SMPS Advantage – Simplified Standby Supply Over Units with Linear Supplies
AC IN
SMPS Components:
•
•
•
AVR3311CI Standby Power Supply Block Diagram
1‐ 5.2VDC supply
1 ‐ Standby/On Relay
1 ‐ Control Line from CPU
Section Summary
1.
2.
Power Supplies Convert Electrical Power
Most Power Supplies have three functions
•
Conversion (mandatory)
•
Isolation (Optional)
•
Regulation (Optional)
3. SMPS have the following advantages over Linear Supplies:
•
•
•
Efficiency
Smaller Components
Simple on /off switching
SMPS
Operation
MARANTZ /DENON SMPS
Schematic
1. Conversion
2. Isolation
3. Regulation
Simplified SMPS Block Diagram
1.
2.
3.
4.
Conversion
Isolation
Regulation
On/Off Control
SMPS Operation is controlled by the SMPS Control IC
SMPS Control IC
SMPS Control IC
TOP258MG
Features Include:
1. Internal Switching
Device
2. Built –in Soft Start
3. Internal
Overvoltage/ Under
voltage Protection
4. Internal Over
Current Protection
SMPS IC Pin Functions
Drain (D)
Main Switch. This pin also
provides start voltage to
Control input (C).
Control (C)
Regulator feedback and
startup control input
Current Limit (X)
External current limit input
and on/off control.
Voltage Monitor (V)
Over voltage, Under
voltage monitor input.
How Does It Work?
This SMPS Has Three Stages of Operation:
1. Startup
2. Run
3. Fault Detect & Protection
Startup Process
1.
Raw B+
4.
5.
4.
Step
1. AC to DC Conversion ‐‐ Raw B+
2. On/Off Transistors Switched ON
3. Control pin (C) climbs to 5.8 Volts
4. Switching Drive Starts
Note: Capacitance on control pin (C)
provides current boost for switch drive.
5. Soft start begins
2.
3
.
Run
Run Operation
1. PWM drive signal develops transformer
secondary current which is rectified and
filtered to generate secondary voltages.
2. Secondary Voltages Developed and supplied
to load.
3. Control Pin (C) of PWM IC receives output
voltage Sample. This sample is passed
through the Opto Isolator and sent to the
Control input of the control IC
4. Control Pin voltage varies by as much 1
Volt (4.8 to 5.8 volts) depending on load. The
PWM duty cycle decreases as the voltage on
the control pin increases.
Protection
Protection Shutdowns
1. OV/UV
Over Voltage/Under Voltage
2. Current Limit
3. Low Line
4. Regulation OK
Over voltage/Under voltage Protect
Purpose:
1. Detects excessive AC line voltage
and disables SMPS control IC
2. Monitors secondary output and
disables SMPS control IC if
excessive.
3. At power up and power down
disables start up process.
How?
1. Monitors sample of Raw B+
2. Monitors Secondary B+ voltage
Failure Mode
A. When >3.1V or <2.5V is detected
at V pin, drive from D pin is
disabled and SMPS IC is place in
slow Start Mode. In slow start
mode, C pin has 1 PVV saw tooth
wave riding on 4.8VDC.
B. If error Condition last >100
microseconds, SMPS IC will shut
down
Failure Modes
Over Current Protection
Purpose:
Detects excessive current in
switching device and disables
power supply when a excessive
current condition exists.
How?
SMPS IC internally monitors
current through the D and S
terminals. The resistor value on
the X pin establishes the
acceptable current level
Failure Mode
When an excessive current
condition is detected, drive at D
pin is disabled immediately and
SMPS IC is placed in slow start. If
condition still exists, the process
will repeat.
Over Current
Trip Point
Low Line Protection
Purpose:
Detects when Raw B+ drops below 97
Volts DC
How?
When Raw B+ drops below 97 VDC,
the switch transistors are off and the
SMPS IC will not drive the transformer
Failure Mode
Base of transistors are 0 VDC and pin X
is 1.4 VDC
Out OF Regulation
Section Summary
1. Three SMPS Operation Modes:
1. Startup
2. Run
3. Protection
2. Four Protection Conditions:
1.
2.
3.
4.
OV/UV
Current Limit
Low Line
Regulation OK
Troubleshooting
No DC Output
Normal Voltages
15 VPP
Hot Ground
Cold Ground
Troubleshooting Setup
Step 3.
With an Isolation
transformer,
supply AC power
Step 1.
Remove SMPS
from Unit
Step 2.
Install a 20 Ohm 1
watt Load resistor
between SMPS
output and cold
ground
Troubleshooting
Step 1. Check for 5.2 VDC at output of supply
If Present, power supply is good and suspect a load issues in the unit
Troubleshooting
Step 2. With an Oscilloscope, monitor C input (pin 3) of control IC
(next Slide)
Waveform Looks like this
Suspect SMPS IC is shutdown. This could be due to
UV/OV Protect or SMPS IC is not being switched on.
Check
1. Voltage on X pin (pin 2 of IC102) = 1.4 VDC
A. If No, suspect
2. Check voltage on V pin (pin 1) = 2.9 VDC
A. If no, suspect
B. If yes, suspect
Next Slide
Waveform Looks like this
Suspect over current protect is being tripped
Check the se components
Next Slide
Waveform Looks like this
Suspect an open in the run supply for the C input
(pin 3) or a issue in the regulator feedback signal
path.
Check
TROUBLESHOOTING
No Regulation
Step 1
Step 2
Connect DC
Power
Supply
Step 3
Check DC
Voltages
The End