TDA46052 - N/A - Datasheet.Directory

The IC TDA 4605-2 controls the MOS-power transistor and performs all necessary regulation and

monitoring functions in free running flyback converters. Because of the fact that a wide load range

is achieved, this IC is applicable for consumer as well as industrial power supplies.

The serial circuit and primary winding of the flyback transformer are connected in series to the input

voltage. During the switch-on period of the transistor, energy is stored in the transformer. During the

switch-off period the energy is fed to the load via the secondary winding. By varying switch-on time

of the power transistor, the IC controls each portion of energy transferred to the secondary side

such that the output voltage remains nearly independent of load variations. The required control

information is taken from the input voltage during the switch-on period and from a regulation winding

during the switch-off period. A new cycle will start if the transformer has transferred the stored

energy completely into the load.

Type Ordering Code Package

TDA 4605-2 Q67000-A5020 P-DIP-8-1

Control IC for Switched-Mode Power Supplies

using MOS-Transistors

Bipolar IC

TDA 4605-2

P-DIP-8-1

Features

●Fold-back characteristics provides overload protection for

external components

●Burst operation under secondary short-circuit condition

implemented

●Protection against open or a short of the control loop

●Switch-off if line voltage is too low (undervoltage switch-off)

●Line voltage depending compensation of fold-back point

●Soft-start for quiet start-up without noise generated by the

transformer

●Chip-over temperature protection implemented (thermal

shutdown)

●On-chip ringing suppression circuit against parasitic

oscillations of the transformer

Semiconductor Group 54 06.94

Semiconductor Group 55

TDA 4605-2

In the different load ranges the switched-mode power supply (SMPS) behaves as follow:

No load operation

The power supply is operating in the burst mode at typical 20 to 40 kHz. The output voltage can be

a little bit higher or lower than the nominal value depending of the design of the transformer and the

resistors of the control voltage divider.

Nominal operation

The switching frequency is reduced with increasing load and decreasing AC-voltage. The duty

factor primarily depends on the AC-voltage.

The output voltage is only dependent on the load.

Overload point

Maximal output power is available at this point of the output characteristic.

Overload

The energy transferred per operation cycle is limited at the top. Therefore the output voltages

declines by secondary overloading.

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TDA 4605-2

Pin Definitions and Functions

Pin No. Function

1Information Input Concerning Secondary Voltage. By comparing the

regulating voltage - obtained from the regulating winding of the transformer - with

the internal reference voltage, the output impulse width on pin 5 is adjusted to the

load of the secondary side (normal load, overload, short-circuit, no load).

2Information Input Regarding the Primary Current. The primary current rise in

the primary winding is simulated at pin 2 as a voltage rise by means of external

RC-circuit. If a voltage level is reached which is derived from the control voltage

at pin 1, the output impulse at pin 5 is terminated. The RC-circuit is used to set

the maximum power of the foldback point.

3Input for Primary Voltage Monitoring: In the normal operation V3 is moving

between the thresholds V3H and V3L (V3H > V3 > V3L).

V3<V3L: SMPS is switched OFF (line voltage too low).

V3 > V3H : Compensation of the overload point regulation (controlled by pin 2)

starts at V3H :V3L = 1.7.

4Ground

5Output: Push-pull output for charging or discharging the gate capacity of the

power MOSFET-transistor.

6Supply Voltage Input. From the voltage at pin 6 a stable internal reference

voltage VREF and the switching thresholds V6A ,V6E ,V6 max and V6 min for the

supply voltage detector are derived. If V6 > V6E then VREF is switched on. The

reference voltage will be switched off if V6<V6A . In addition the logic is only

enable, for V6 min < V6< V6 max .

7Input for Soft-Start and Integrator Circuit. The capacitor connected to ground

causes a slow increase of the duration of the output pulse during start-up and an

integrating response of the control amplifier.

8Input for the Feedback of the Oscillator. After the oscillations of the SMPS

started, every transition of the feedback voltage through zero (falling edge)

triggers an output pulse at pin 5. The trigger threshold is at + 50 mV typical.

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TDA 4605-2

Block Diagram

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TDA 4605-2

Circuit Description

Application Circuit

The application circuit shows a flyback converter for video recorders with an output power rating of

70 W. The circuit is designed as a wide-range power supply for AC-line voltages of 180 to 264 V.

The AC-input voltage is rectified by the bridge rectifier GR1 and smoothed by C1. The NTC limits

the rush-in current.

The IC includes an internal circuit to avoid the turn-on of the power transistor T1 because of static

charges applied to the transistors gate, during the turn-off state of the IC. The resistor R13 helps to

limit the spectrum of the radiated noise.

During the conductive phase of the power transistor T1 the current rise in the primary winding

depends on the winding inductance and the mains voltage.

The network consisting of R4-C5 is used to create a model of the sawtooth shaped rise of the

collector current. The resulting control voltage is fed into pin 2 of the IC. The RC-time constant given

by R4-C5 must be designed that way that driving the transistor core into saturation is avoided.

The ratio of the voltage divider R10/R11 is fixing a voltage level threshold. Below this threshold the

switching power supply shall stop operation because of the low mains voltage. The control voltage

present at pin 3 also determines the correction current for the foldback point.

This current added to the current flowing through R4 and represents an additional charge to C5 in

order to reduce the turn-on phase of T1. This is done to stabilize the fold-back point even under

higher mains voltages.

The control of the switched-mode power supply is done by means of a control voltage applied to

pin 1. The control voltage of winding n1 during the off-period of T1 is rectified by D3 smoothed byC6

and stepped down at an adjustable ratio by R5,R6 and R7. The primary peak current, is adjusted

by the IC so that the voltage applied across the control winding, and hence the output voltages, are

at the desired level.

When the energy stored in the transformer is transferred into the load the control voltage passes

through zero. The IC detects the zero crossing via the series R9 connected to pin 8. But zero

crossings of the control voltage can also be produced by ringing of the transformer after the turn-off

of the power transistor for T1 or when a short-circuit is applied to the output of the SMPS.

The capacitor C8 is connected to pin 7. During the start-up phase this capacitor assures pulses with

a shorter duty cycle in order to keep the operating frequency outside the audible frequency range.

On the secondary side of the transformer 3 output voltages are produced using the windings n2 to

n5, rectified by D4 to D6 and smoothed byC9 to C11 . The resistor R12 is used as a bleeder resistor,

the resistors with implemented fuse R15 and R16 protect the rectifies against short circuits in the

output circuits, which are designed to supply only small loads.

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TDA 4605-2

Block Diagram

Pin 1

In the control and overload amplifier the control voltage applied to this pin is compared with a stable

internal reference voltage V. The output signal of this stage is fed to the "stop" comparator. If the

control voltage is rather small at pin 1 an additional current is added by means of current source

which is controlled according the level at pin 7. This additional current is virtually reducing the

control voltage present at pin 1.

Pin 2

A voltage proportional to the drain current of the switching transistor is generated by means of an

external RC-combination in conjunction with the internal functional block primary current / voltage

converter. The output of this converter is controlled by the internal functional block "logic" and is

also connected to the internal reference voltage V2B . If the voltage V2 exceeds the output voltage

of the "control and overload amplifier" the stop comparator will reset the control logic. Consequently

the output of pin 5 is switched to low potential. Further inputs for the logic stage are the outputs of

the start impulse generator with the stable reference potential VST , the supply voltage monitoring

circuit as well as the primary voltage supervision circuit.

Pin 3

The primary voltage applied here via a voltage divider is used to stabilize the fold-back point. In

addition the logic is disable if - in comparison with the internal reference voltage VV - a mains

undervoltage condition is detected.

Pin 4

Ground

Pin 5

In the output stage the output signals from the "logic" block are converted into driving signals

suitable for power MOS-transistors.

Pin 6

From the supply voltage V6 applied to this pin internally a stable reference voltage VREF as well as

the switching thresholdV6A ,V6E ,V6 max andV6 min , for the supply voltage monitor section of the IC.

All other inter reference value (VR,V2B ,VST and Vv) are derived for VREF . If V6>V6E the VREF

voltage source is switched on and the source is switched off if V6<V6A . In addition the logic is

enable only if V6 min < V6 < V6 max .

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TDA 4605-2

Pin 7

By means of a resistor pin 7 is connected with the output of the control amplifier. If V1 is approx.

equal to the control voltage VR the control amplifier has a proportional integrating control

characteristics. The response of the control loop is derived from the capacitor connected to pin 7. If

V1 is equal to 0 V the control and overload amplifier is generating a ramp-up function using the

capacitor connected to pin 7.

Pin 8

The zero crossing detector controlling the logic block recognizes the complete discharge of the

energy stored in the transformator core by detecting the zero crossing the positive to negative

voltage transition of the voltage at pin 8. This enables the logic for a new pulse. Parasitic oscillations

occurring at the end of a pulse cannot lead to a new pulse because of an internal circuit which

inhibits the zero detector for a certain dead time tUL after the end of each pulse.

Start-Up Behaviour

The start-up behaviour of the application circuit (which is given on page 68) is explained in the

diagrams on page 70 for a line voltage barely above the lower acceptable lower limit of the mains

voltage. After applying the mains voltage at the timet0 the following built up of different voltages can

be seen:

–V6 corresponding to the half-wave charge current over R1

–V2 to V2 max (typically 6.6 V)

–V3 to the value determined by the divider R10/R11

The current drawn by the IC in this case is less than 0.8 mA.

If V6 reaches the threshold (at the time t1 in the diagram), the IC internal reference voltage is

switched on. The supply current drawn by the IC rises to 12 mA max.. The primary current/voltage

converter reducesV2 down toV2B and the start pulse generator generates the start pulses from time

point t5 to t6 in the diagram. The feedback to pin 8 starts the next pulse and so on. The width of all

pulses including the start pulse are controlled by means of the control and overload amplifier. After

turn on the IC is generating a signal at pin 7 which slowly ramping up. This signal is used to increase

the duration of the output pulses slowly (soft-start function). The max. output pulse width is limited

by means of the overload amplifier. If the feedback control voltage V1 is increasing, the overload

amplifier allows the generation of output pulses with a wider pulse width. The max. pulse width is

reached at time t2 in the diagram (V2 = V2S max). The IC is then operating at the fold-back point.

Thereafter the peak values ofV2 decrease rapidly, because of the IC control range. The control loop

is in a steady, operational state.

If the voltage V6 falls below the switch-off threshold V6 min before the foldback point is reached, the

attempt to start the SMPS is aborted (pin 5 is switched to low). As the internal circuits of the IC

remain switched on, V6 further decreases to V6A . The IC switches off; V6 can rise again (time t4 in

the diagram) and new start-up attempt begins at time t1.

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TDA 4605-2

If the voltage level of the rectified mains voltage is reduced strongly under the influence of the

applied load it can happen that V3 is below the voltage level V3A - please refer to the time t3 in the

diagram. This is because if an attempt is made to start the SMPS with a too low mains voltage. The

internal primary voltage monitor circuit then clamps the voltage V3 to the voltage level V3S until the

IC switches off (V6<V6A). After this a new attempt to start the SMPS will begin at the time t1 in the

diagram.

Control Range, Overload and No-Load Behaviour

After the IC has started, it is operating in the control range. The voltage level at pin 1 is typically

400 mV. The gain of the control circuit consist of two parts: at first a fixed proportional part which is

internally fixed and an integrating part which can be set by means of the external capacitor at pin 7.

If the load is applied to the output of the SMPS, the control and overload amplifier allows wider

pulses (V5 = "H") .The peak voltage value at pin 2 increases up to V2S max . If the secondary load is

increased further the overload amplifier begins to reduce the pulse width of the output pulse. This

point is referred to as the fold-back point of the power supply. Because of the fact that the IC supply

voltage is directly proportional to the secondary voltage, the supply voltage V6 will be reduced

according to the behaviour of the control circuit under the overload condition. If V6 falls below the

value V6 min , the IC will operate in the burst mode. Because of the large time constant of the start-

up circuit which is operating with half-wave rectification, only a small output power is transferred into

the load during the secondary short-circuit of the SMPS. The overload amplifier reduces the output

pulse width down to the pulse widthtpk . This pulse width must remain possible in order to permit the

IC to start up without problems from the virtual short-circuit, which every switching on with V1=0 is

representing.

If no load is applied to the secondary side, the output pulses (V5= H) become shorter.

If the pulse width is reduced be low a certain internal limit the IC will suppress some of the output

pulses. If the load is reduced further because of the decreasing duty cycle the measurement error

of the rectifier network (R8, D3, C6 of the application circuit) is increasing and therefore the

secondary output voltage will increase, too. If the IC is operating with small pulse width of the output

pulse the control amplifier applies an additional current to the control amplifier in order to reduce the

output voltage. The value of the additional current depends on the size of the resistorsR5,R8,R7.

This can be used to compensate the increase of the secondary voltages.

Behaviour if the Chip Temperature Exceeds Predefined Limits

An integrated protection circuit against over temperature disables the internal logic if the chip

temperature is too high. The internal logic automatically checks the chip temperature and restart the

SMPS as soon as the temperature decreases to a permissible level.

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TDA 4605-2

*) tp= pulse width

v= duty circle

Absolute Maximum Ratings

TA = – 20 to 85 ˚C; all voltages relatives to Vpp

Parameter Symbol Limit Values Unit Remarks

min. max.

Voltages pin 1

pin 2

pin 3

pin 5

pin 6

pin 7

– 0.3

VSupply voltage

Currents pin 1

pin 2

pin 3

pin 4

pin 5

pin 6

pin 7

pin 8

– 1.5

– 0.5

– 5

1.5

0.5

tp≤ 50 µs; v ≤ 0.1*)

tp≤ 50 µs; v ≤ 0.1

Junction temperature Tj125 ˚C

Storage temperature Tstg – 40 125 ˚C

Operating Range

Supply voltage V67.5 15.5 V IC "on"

Ambient temperature TA– 20 85 ˚C

Heat resistance

Junction environment

Junction package Rth JE

Rth JG

100

70 K/W

K/W measured at pin 4

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TDA 4605-2

Characteristics

TA = 25 ˚C; VS = 10 V

Parameter Symbol Limit Values Unit Test Condition Test

Circuit

min. typ. max.

Start-Up Hysteresis

Start-up current drain I6E0 0.6 0.8 mA V6 = V6E 1

Switch-on voltage V6E 11 12 13 V 1

Switch-off voltage V6A 4.5 5 5.5 V 1

Switch-on current I6E1 11 mA V6 = V6E 1

Switch-off current I6A1 10 mA V6 = V6A 1

Voltage Clamp (V6 = 10 V, IC switched off)

At pin 2 (V6≤V6E)

At pin 3 (V6≤V6E)V2 max

V3 max

5.6

5.6 6.6

6.6 8

VI2 = 1 mA

I3 = 1 mA 1

Control Range

Control input voltage V1R 390 400 410 mV 2

Voltage gain of the

control circuit in the

control range

–VR43 dB VR = d

(V2S – V2B)/– dV1

f = 1 kHz

Primary Current Simulation Voltage

Basic value V2B 0.97 1.00 1.03 V 2

Overload Range and Short-Circuit Operation

Peak value in the

range of secondary

overload

V2O 2.9 3.0 3.1 V V1 = V1R – 10 mV 2

Peak value in the

range of secondary

short-circuit operation

V2S 2.2 2.4 2.6 V V1 = 0 V 2

Fold-Back Point Correction

Fold-back point

correction current –I2300 500 650 µAV3 = 3.7 V 1

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TDA 4605-2

Generally Valid Data (V6 = 10 V)

Voltage of the Zero Transition Detector

Positive clamping

voltage V8P 0.75 V I8 = 1 mA 2

Negative clamping

voltage V8N – 0.2 V I8 = – 1 mA 2

Threshold value V8S 40 50 mV 2

Suppression of

transformer ringing tUL 4 4.5 5.5 µs2

Input current – I804µAV

= 0

Push-Pull Output Stage

Saturation voltages

Pin 5 sourcing

Pin 5 sinking

VSat0

VSatV

1.5

1.0

1.4

2.0

1.2

1.8

I5 = – 0.1 A

I5 = + 0.1 A

I5 = + 0.5 A

Output Slew Rate

Rising edge + dV5/dt20 V/µs2

Falling edge + dV5/dt50 V/µs2

Reduction of Control Voltage

Current to reduce the

control voltage –I150 µAV7 = 1.1 V

Characteristics (cont’d)

TA = 25 ˚C; VS = 10 V

Parameter Symbol Limit Values Unit Test Condition Test

Circuit

min. typ. max.

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TDA 4605-2

Protection Circuit

Undervoltage

protection

for V6: voltage at

pin 5 = V5 min

if V6 < V6 min V6 min 7.0 7.25 7.5 V 2

Undervoltage

protection for V6:

voltage at

pin 5 = V5 min

if V6 > V6 max V6 max 15.5 16 16.5 V 2

Undervoltage

protection for VAC :

voltage at

pin 5 = V5 min

if V3 < V3A V3A 985 1000 1015 mV V2 = 0 V 1

Over temperature at

the given chip the

temperature IC will

switch V5 to V5 min

Tj150 ˚C 2

Voltage at pin 3 if one

of the protection

functions was

triggered;

(V3 will be clamped

until V6 < V6A)V3Sat 0.4 0.8 V I3 = 750 µA1

Current drain during

burst operation I68mAV

= V2 = 0 V 1

Characteristics (cont’d)

TA = 25 ˚C; VS = 10 V

Parameter Symbol Limit Values Unit Test Condition Test

Circuit

min. typ. max.

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TDA 4605-2

Test Circuit 1

Test Circuit 2

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TDA 4605-2

Application Circuit

Semiconductor Group 68

TDA 4605-2

Diagrams

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TDA 4605-2

Semiconductor Group 70

TDA 4605-2

Start-Up Hysteresis

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TDA 4605-2

Operation in Test Circuit 2

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TDA 4605-2

Start-Up Current as a Function of the

Ambient Temperature Overload Point Correction as a Function of

the Voltage at Pin 3

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TDA 4605-2

Recommended Heat Sink by 60 ˚C Ambient Temperature

Narrow Range 180 V ... 120 V ~

Narrow Range 90 V ... 270 V ~