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Control ICs for Switched-Mode Power Supplies
TDA 4601
Bipolar IC
Features
q q q q q
Direct control of the switching transistor Low start-up current Reversing linear overload characteristic Base current drive proportional to collector current Protective circuit in case of disturbance
P-SIP-9-1
Type TDA 4601
Ordering Code Q67000-A2379
Package P-SIP-9-1
The integrated circuit TDA 4601/D is designed for driving, controlling and protecting the switching transistor in self-oscillating flyback converter power supplies as well as for protecting the overall power supply unit. In case of disturbance, the rise of the secondary voltage is prevented. In addition to the ICs application range including TV-receivers video tape recorders, hifi devices and active loudspeakers, it can also be used in power supply units for professional applications due to its wide control range and high voltage stability during increased load changes.
Semiconductor Group
7
06.94
TDA 4601
Pin Definitions and Functions Pin No. 1 2 3 4 5 6 7 8 9 Function
VREF output
Zero passage identification Input control amplifier, overload amplifier Collector current simulation Connection for additional protective circuit Ground (rigidly connected to substrate mounting plate) DC-output for charging coupling capacitor Pulse output - driving of switching transistor Supply voltage
Block Diagram
Semiconductor Group
8
TDA 4601
Circuit Description The TDA 4601 is designed for driving, controlling and protecting the switching transistor in flyback converter power supplies during start-up, normal and overload operations as well as during disturbed operation. In case of disturbance the drive of the switching transistor is inhibited and a secondary voltage rise is prevented. Start-Up The start-up procedures (on-mode) include three consecutive operating phases as follows: 1. Build-Up of Internal Reference Voltage The internal reference voltage supplies the voltage regulator and effects charging of the coupling electrolytic capacitor connected to the switching transistor. Current consumption will remain at I9 < 3.2 mA with a supply voltage up to V9 approx. 12 V. 2. Enabling of Internal Voltage - Reference Voltage V1 = 4 V Simultaneously with V9 reaching approx. 12 V, an internal voltage becomes available, providing all component elements, with the exception of the control logic, with a thermally stable and overload-resistant current supply. 3. Enabling of Control Logic In conjunction with the generation of the reference voltage, the current supply for the control logic is activated by means of an additional stabilization circuit. The integrated circuit is then ready for operation. The start-up phase above described are necessary for ensuring the charging of the coupling electrolytic capacitor, which in turn supplies the switching transistor. Only then is it possible to ensure that the transistor switches accurately. Normal Operating Mode / Control Operating Mode At the input of pin 2 the zero passages of the frequency provided by the feedback coil are registered and forwarded to the control logic. Pin 3 (control input, overload and standby identification) receives the rectified amplitude fluctuations of the feedback coil. The control amplifier operates with an input voltage of approx. 2 V and a current of approx. 1.4 mA. Depending on the internal voltage reference, the overload identification limits inconjunction with collector current simulator pin 4 the operating range of the control amplifier. The collector current is simulated by an external RC-combination present at pin 4 and internally set threshold voltages. The largest possible collector current applicable to the switching transistor (point of return) increases in proportion to the increased capacitance (10 nF). Thus the required operating range of the control amplifier is established. The range of control lies between a DC-voltage clamped at 2 V and a sawtooth - shaped rising ACvoltage, which can vary up to a max. amplitude of 4 V (reference voltage). During secondary load reduction to approx. 20 W, the switching frequency is increased (approx. 50 kHz) at an almost constant pulse duty factor (1:3). During additional secondary load decreases to approx. 1 W, the switching frequency increases to approx. 70 kHz and pulse duty factor to approx. 1:11. At the same time collector peak current is reduced to < 1 A.
Semiconductor Group
9
TDA 4601
The output levels of the control amplifier as well as those of the overload identification and collector current simulator are compared in the trigger and forwarded to the control logic. Via pin 5 it is possible to externally inhibit the operations of the IC. The output at pin
pin 8 will be inhibited when voltages of ----------- 0.1 are present at pin 5. 2
Flipflops for controlling the base current amplifier and the base current shut-down are set in the control logic depending on the start-up circuit, the zero passage identification as well as on the enabling by the trigger. The base current amplifier forwards the sawtoothspahed V4 voltage to the output of pin 8. A current feedback with an external resistor (R = 0.68 ) is present between pin 8 and pin 7. The applied value of the resistor determines the max. amplitude of the base driving current for the switching transistor. Protective Operating Mode The base current shut-down activated by the control logic clamps the output of pin 7 to 1.6 V. As a result, the drive of the switching transistor is inhibited. This protective measure is enabled if the supply voltage at pin 9 reaches a value 6.7 V or if voltages of
V REF
----------- 0.1 are present at pin 5. 2
In case of short-circuits occurring in the secondary windings of the switched-mode power supply, the integrated circuit continuously monitors the fault conditions. During secondary, completely loadfree operation only a small pulse duty factor is set. As a result the total power consumption of the power supply is held at N = 6 ... 10 W during both operating modes. After the output has been inhibited for a voltage supply of 6.7 V, the reference voltage (4 V) is switched off if the voltage supply is further reduced by V9 = 0.6 V. Protective Operating Mode at Pin 5 in Case of Disturbance The protection against disturbances such as primary undervoltages and/or secondary overvoltages (e.g. by changes in the component parameters for the switched-mode power supply) is realized as follows: Protective Operating Mode with Continuous Fault Condition Monitoring In case of disturbance the output pulses at pin 8 are inhibited by falling below the protective threshold V5 , with a typical value of V1/2. As a result current consumption is reduced (I9 14 mA at V9 = 10 V). With a corresponding high-impedance start-up resistor *), supply voltage V9 will fall below the minimum shut-down threshold (5.7 V) for reference voltage V1 . V1 will be switched off and current consumption is further reduced to I9 3.2 mA at V9 10 V. Because of these reductions in current consumption, the supply voltage can rise again to reach the switch-on threshold of V9 12.3 V. The protective threshold at pin 5 is released and the power supply is again ready for operation.
V REF
Semiconductor Group
10
TDA 4601
In case of continuing problems of disturbance (V5 V1/2 0.1 V) the switch-on mode is interrupted by the periodic protective operating mode described above, i.e. pin 8 is inhibited and V9 is falling, etc. Switch-On in the Wide Range Power Supply (90 Vac to 270 Vac) (application circuit 2) Self-oscillating flyback-converters designed as wide range power supplies require a power source independent of the rectified line voltage for TDA 4601. Therefore the winding polarity of winding 11/13 corresponds to the secondary side of the flyback converter transformer. Start-up is not as smooth as with an immediately available supply voltage, because TDA 4601 has to be supplied by the start-up circuit until the entire secondary load has been charged. This leads to long switch-on times, especially if low line voltages are applied. However, the switch-on time can be shortened by applying the special start-up circuit (dotted line). The uncontrolled phase of feedback control winding 15/9 is used for activating purposes. Subsequent to activation, the transistor T1 begins to block when winding 11/13 generates the current supply for TDA 4601. Therefore, the control circuit cannot be influenced during operation.
Semiconductor Group
11
TDA 4601
Absolute Maximum Ratings Parameter Supply voltage Voltages Reference output Zero passage identification Control amplifier Collector current simulation Blocking input Base current cut-off point Base current amplifier output Currents Zero passage identification Control amplifier Collector current simulation Blocking input Base current cut-off point Base current amplifier output Junction temperature Storage temperature range Thermal resistances: system-air TDA 4601 system-case TDA 4601 system-air 1) TDA 4601-D 2) TDA 4601-D system-case Symbol Limit Values min. max. 20 V 0 Unit
V9
V1 V2 V3 V4 V5 V7 V8
0 0.6 0 0 0 0 0
6 0.6 3 8 8
V V V V V V V
V9 V9
Il i2 Il 3 Il 4 Il 5 IQ 7 IQ 8 Tj Tstg Rth SA Rth SC Rth SA Rth SA1
5 3 0 0 1 1.5 40
5 3 5 5 1.5 0 125 125 70 15 60 44
mA mA mA mA A A °C °C K/W K/W K/W K/W
Semiconductor Group
12
TDA 4601
Absolute Maximum Ratings (cont'd) Parameter Symbol Limit Values min. Operating Range Supply voltage Case temperature TDA 4601 Ambient temperature range 3) TDA 4601-D
1) Case soldered on PC-board without cooling surface 2) Case soldered on PC-board with copper-clad 35 µm layer, cooling surface 25 cm2 3)
Unit
max.
V9 TC TA
7.8 0 0
18 85 70
V °C °C
Rth SA1 = 44 K/W and PV = 1 W
Semiconductor Group
13
TDA 4601
Characteristics TA = 25 °C according to measurement circuit 1 and diagram Parameter Symbol min. Start Operation Current consumption (V1 not yet switched on) V9 = 2 V V9 = 5 V V9 = 10 V Switching point for V1 Normal Operation Limit Values typ. max. Unit
I9 I9 I9 V9
11.0
1.5 2.4 11.8
0.5 2.0 3.2 12.3
mA mA mA V
V9 = 10 V; Vcont = 10 V; Vclock = ± 0.5 V; f = 20 kHz
duty cycle 1:2 after switch-on Current consumtion Vcont = 10 V Vcont = 0 V Reference voltage I1 < 0.1 mA I1 < 5 mA Temperature coeffiecient of reference voltage Control voltage Vcont = 0 V Collector current simulation voltage
I9 I9 V1 V1 TC1 V3 V4*) V4 *) V5 VQ7 *) VQ8 *) VQ8 V2 *)
110 50 4.0 4.0 2.3 1.8 0.3 6.0 2.7 2.7 1.6
135 75 4.2 4.2 10 3 2.6 2.2 0.4 7.0 3.3 3.4 2.0 0.2
160 100 4.5 4.5
mA mA V V 1/K
2.9 2.5 0.5 8.0 4.0 4.0 2.4
V V V V V V V V
Vcont = 0 V Vcont = 0 V/ 10 V
Clamping voltage Output voltages Vcont = 0 V Vcont = 0 V Vcont = 0 V/ 10 V Feedback voltage
*) DC-component only
Semiconductor Group
14
TDA 4601
Protective Operation V9 = 10 V; Vcont = 10 V; Vclock = 0.5 V; f = 20 kHz; duty cycle 1:2 Parameter Current consumption V5 < 1.9 V Switch-off voltage Symbol min. Limit Values typ. 22 1.5 2.1 max. 28 1.8 2.5 mA V V Unit
I9 VQ 7 V4
14 1.3 1.8
V5 < 1.9 V
Switch-off voltage
V5 < 1.9 V
Blocking input Blocking voltage Vcont = 0 V Supply voltage blocked for V8
V5 V4
V9
V1 V1 ----- 0.1 ----2 2 6.7 0.3 7.4 0.6 7.8 1.0
V V V
Vcont = 0 V V1 off (with further reduction of V9)
Characteristics TA = 25 °C; according to measurement circuit 2 Parameter Switching time (secondary voltage) Voltage variation N3 = 20 W Voltage variation N3 = 15 W S3 = closed V2 sec S2 = closed V2 sec V2 sec 500 20 75 1000 30 mV V kHz 100 500 mV Symbol min. Limit Values typ. 350 max. 450 ms Unit
tON
Standby operation S1 = open secondary useful load = 3 W
f
70
The cooling conditions have to be optimized with regard to maximum ratings (TA ; Tj ; Rth JC ; Rth SA).
Semiconductor Group
15
TDA 4601
Circuit Diagram
Semiconductor Group
16
TDA 4601
Test and Measurement Circuit 1
Test Diagram: Overload Operation Semiconductor Group 17
TDA 4601
Wide range from 80 to 270 Vac
Application Circuit 2 Semiconductor Group 18
TDA 4601
Notes on Application Circuit 2 Wide Range SMPS Filtering of the rectified AC-voltage has been increased up to 470 µF to ensure a constant and humfree supply at Vline = 80 Vac. The stabilized phase is tapped for supplying the IC. In order to ensure good start-up conditions for the SMPS in the low voltage range, the non-stabilized phase of winding 13/15 is used as a starting aid (BD 139), which is turned off after start-up by means of Z-diode C12. In comparison to the 220 Vac standard circuit, however, the collector-emitter circuit had to be altered to improve the switching behavior of BU 208 for the entire voltage range (80 to 270 Vac). Diode BY 231 is necessary to prevent inverse operation of BU 208 and may be integrated for switching times with a secondary power < 75 W (BU 208 D). Compared to the IC TDA 4600-2, the TDA 4601 has been improved in turn-off during under-voltage at pin 5. The TDA 4601 is additionally provided with a differential amplifier input at pin 5, enabling precise turn-off at the output of pin 8 accompanied by hysteresis. For wide range SMPS, TDA 4601 is recommendable instead of TDA 4600-2. If a constant quality standard equal to that of the standard circuit is to be maintained, wide range SMPS (80 to 270 Vac) with secondary power of 120 W can only be implemented at the expense of time.
Semiconductor Group
19
TDA 4601
Supplements to Application Circuit 2 Efficiency versus Output Power
Efficiency versus Output Power
Semiconductor Group
20
TDA 4601
Supplements to Application Circuit 2 Load Characteristics V2sec = f (I2sec)
Output Voltage V2sec (line change)
Semiconductor Group
21
TDA 4601
Further Applications
Application Circuit 3 Semiconductor Group 22
TDA 4601
Notes on Application Circuit 3 Fully Insulated, Clamp-contacted PTC-Thermistor Suitable for SMPS-Applications at Increased Start-Up Currents The newly developed PTC-thermistor Q63100-P2462-J29 is designed for applications in SMPS as well as in various other electronic circuits, which, for example, receive the supply voltage directly from the rectified line voltage and require an increased current during turn-on. Used in the flyback converter power supply of TV-sets, an application proved millions of times over, the new PTCthermistor in the auxiliary circuit branch has resulted in a power saving of no less than 2 W. This increase in efficiency has a highly favorable effect on the standby operation of TV-sets. The required turn-on current needs only 6 to 8 s until the operating temperature of the PTCthermistor is reached. Low thermal capacitance of the PTC-thermistor allows the circuit to be operated again after no more than 2 s. Another positive feature is the improved short-circuit strength. The clamp contacts permit more or less unlimited switching operations and thus guarantee high reliability. A flame-retardant plastic package and small dimensions are additional advantages of this newly developed PTC-thermistor.
Technical Data Parameter Breakdown voltage at TA = 60 °C Resistance at TA = 25 °C Resistance tolerance Trip current (typ.) Residual current at VA max Max. application voltage Reference temperature (typ.) Temperature coefficient (typ.) Max. operating current Storage temperature range Symbol Limit Values 350 5 25 20 2 265 190 26 0.1 25 to 125 Unit V k % mA mA V °C %/K A °C
VBD rms R 25
R 25
IK IR Vop max rms TREF TC I max Tstg
Semiconductor Group
23
TDA 4601
Application Circuit 4 Semiconductor Group 24
TDA 4601
Notes on Application Circuit 4 Improved Load Control and Short-Circuit Characteristics Turn-on is the same as for circuit 3. To make the price more attractive, switching transistor BU 508 A was selected. To ensure optimum standby conditions, the capacitance between pins 2 and 3 was increased to 100 pF. Z- diode C6.2 transfers control voltage Vcont directly to pin 3 resulting in improved load control. Design and coupling conditions of various flyback transformers were sometimes a reason for overshoot spectra, which, despite the RC-attenuating element 33 x 22 nF and the 10-k resistor, even penetrated across the feedback winding 9/15 to the zero passage indicator input (pin 2) and activated double and multiple pulses in the IC. Double and multiple pulses, however, lead to magnetic saturation in the flyback transformer and thus increase the risk of damaging the switchedmode power supply. The larger the quantities of power to be passed, the more easily overshoots are generated. This can be observed around the point of return. The switched-mode power supply, however, reduces its own power to a minimum in all cases of overload or short-circuit. A series resonant circuit, whose resonance corresponds to the transformer's selfoscillation, was created by combination of the 4.7-µH inductance and the 22-nF capacitance. This resonant circuit short-circuits overshoots via a 33- resistor.
1 f = ----------------- 500 kHz 2 LC
Semiconductor Group
25
TDA 4601
Application Circuit 5 Semiconductor Group 26
TDA 4601
Notes on Application Circuit 5 Highly Stable Secondary Side Power supplies for commercial purposes require highly constant low voltages and high currents which, on the basis of the flyback converter principle, can be realized only under certain conditions, but, on the other hand, are implemented for economical reasons. An electrically isolated flyback converter with a highly stable secondary side must receive the control information from this secondary side. There are only two possibilities for meeting this requirement: either through a transformer which is magnetically isolated from the flyback converter or by means of an optocoupler. The development of CNY 17 has enabled the manufacture of a component suitable for electrical isolation and characterized by high reliability and long-term stability. The IC TDA 4601-D is the sucessor of the TDA 4600-D. It is compatible with its predecessor in all operational functions and in the control of a self-oscillating flyback converter. Pin 3 is the input for the control information, where the latter is compared with the reference voltage prevailing at pin 1 and the control from the optocoupler and subsequently transformed into a frequency/pulse width control. The previous feedback and control information winding is not necessary. The feedback information (zero passage) is obtained from winding 3/4 - supply winding. The time constant chain 330 /3.3 nF and 330 /2.2 nF was implemented in series with 150 µH to prevent interference at pin 2. The LCelement forms a series resonant circuit for overshoots of the flyback converter and short-circuits them.
Semiconductor Group
27
TDA 4601
Application Circuit 6 Semiconductor Group 28
TDA 4601
Notes on Application Circuit 6 Wide Range Plug SMPS up to 30 W Due to their volume and weight, plug SMPS have so far been limited to a restricted primary voltage and a secondary power of no more than 6 W. The line-isolated wide range flyback converter presented here has a variable frequency and is capable of producing a secondary power of 30 W. It is characterized by a compact design with an approx. weight of 400 g. The entire line voltage range of 90 to 260 Vac is stabilized to ± 1.5 % on the secondary side. Load fluctuations between 0.1 and 2 A are regulated to within 5 %. The output (secondary side) is overload, short-circuit, and openloop proof.
Semiconductor Group
29
TDA 4601
Application Circuit 7 Semiconductor Group 30
TDA 4601
Notes on Application Circuit 7 Wide Range SMPS with Reducing Peak Collector Current IC BU 208 for Rising Line Voltage (variable point of return) Wide range SMPS have to be dimensioned at line voltages of 90 to 260 Vac. The difference between the maximum collector current I C BU 208 max and the largest possible limit current IC BU 208 limit which causes magnetic saturation of the flyback transformer and flows through the primary inductance winding 5/7 is to be determined at Vacmin (IC BU 208 limit 1.2 x IC BU 208 max). Then, the transmissible power of the flyback transformer and its value at Vacmax is to be determined. In the standard circuit the collector current IC BU 208 max is almost constant at the point of return independent of the line voltage. The transmissible power on the secondary side, however, increases at the point of return in proportion to the rising rectified line voltage applied (figures 1 and 2). In the wide range SMPS a line voltage ratio of 270/90 = 3/1 is obtained, causing doubling of the transmissible power on the secondary side, i.e. in the wide range SMPS a far too large flyback transformer had to be implemented. The point of return protecting the SMPS against overloads or short circuits, is derived from the time constant at pin 4 t 4 = 270 k x 4.7 nF. Thus, the largest possible pulse width is determined. With the introduction of the 33-k resistor this time constant is reduced as a function of the control voltage applied to winding 13/15, rectified by diode BY 360 and filtered by the 1-µF capacitance, which means that the pulse time becomes shorter. By means of the Z-diode C18 the line voltage level can be defined at which the influence of the time constant correction becomes noticeable. The change in the rectified voltage of winding 13/15 is proportional to the change in the rectified line voltage. At the point of return IC BU 208 the peak collector current has been reduced with the aid of the given values from 5.2 A at 90 Vac to 3.3 A at 270 Vac. The transmissible power at the point of return remains stable between 125 and 270 Vac due to the set activation point of the point of return correction (unbroken curve in figure 2).
Semiconductor Group
31
TDA 4601
Load Characteristics
Figure 1
Figure 2 Semiconductor Group 32