TW201014183A - Pulse-width modulation (PWM)-controlled soft ON/OFF circuit - Google Patents

Abstract

The present invention relates to a pulse-width modulation (PWM)-controlled soft ON/OFF circuit, comprising: an operation transconductance amplifier, a plurality of switches, a plurality of inverters, a controllable-start timer, a RC network and a reference voltage source. The present invention applies a simple design of the circuit structure to realize the controllable soft-start circuit, and it does not need very large capacitor for fitting into the IC chip. Therefore, the PWM-controlled soft ON/OFF circuit can be integrated into the LED driving chip. When the IC chip receives the PWM signal from the exterior, it can make the duty cycle of the feedback average input voltage of the external circuit to the PWM signal to increase proportional ratio to adjust LED brightness by utilizing the PWM signal.

Description

201014183 VIII. If there is a chemical formula in this case, please disclose the chemical formula that best shows the characteristics of the invention: IX. Description of the invention: [Technical field of the invention] The present invention relates to a controllable soft start with pulse width modulation function and A soft-close circuit, in particular, a capacitor capable of being fabricated in an integrated circuit and built in the inside of the chip, and capable of externally inputting the feedback voltage of the feedback terminal and the pulse width modulation signal in the feedback circuit Controllable soft-start and soft-off circuit with pulse width modulation function proportional to Duty Cyde. [Prior Art] Please refer to the first to fourth and seventh figures. In the general led driver chip (2), there is a built-in controllable soft start circuit (4), as shown in the first figure. The controllable soft start circuit (4) 'includes an operational transconductance amplifier (11), a reference voltage source (12), an RC network and a feedback voltage input terminal (182), and a switching circuit output terminal ( 183). The non-inverting input terminal of the operational transconductance amplifier (n) is connected to the reference voltage source (12), and the inverting input terminal of the operational transconductance amplifier (11) is connected to the feedback voltage input terminal (182), and the operation is turned The output of the operational amplifier (11) is connected to the RC network 'and the output of the operational transconductance amplifier (u) is connected to the output of the switching circuit (183); wherein the RC network The RC network 5 201014183 is formed by using a resistor (171) in series with a capacitor (172), and the other end of the resistor (171) is connected to the output terminal of the operational transconductance amplifier (u). The other end of 172) is connected to the ground. Figures 2 to 4 are diagrams showing the relevant voltage waveforms of the controllable soft-start circuit (4) of the conventional application when applied to the LED driver chip (2); at this time, the frequency of the pulse width modulation signal (iWM) is IKHz, Duty Cyde is 10%, 4〇%, and 80%, respectively. In this application, the operational transconductance amplifier (u) has a VG/w of 10uS's resistance (171) of 120 kilohms; due to the limitation of the internal area of the wafer, the capacitance used in the general wafer is only the largest. Can be 100pF~200PF. As can be seen from the waveforms shown in Figures 2 to 4, the output terminal voltage F(10) of the external connection circuit of the feedback driver voltage of the LED driver chip (2) is changed according to the change of the pulse width modulation signal. And at the output end of the LED driver chip (the cut produces a large voltage ripple) and then at the output of the LED driver crystal (the capacitor that is interfaced with 0^^ generates audio noise. Avoid unnecessary noise noise generated by the LED driver chip (7) when dimming with pulse width modulation, and the capacitance (10) used in the controllable soft-start circuit (4) of the circuit type of the thief is often large. Therefore, it is not possible to fabricate the ribs in the form of a circuit, so that the capacitor (172) attached to the controllable soft-start circuit of the conventional mode is externally connected to the outside of the wafer. 6 201014183 [Summary of the Invention] The invention relates to a controllable soft start and soft shutdown circuit with a pulse width modulation function, which realizes a controllable soft start circuit by using a simpler circuit structure design, and does not require a large capacitance. Complete controllable soft start and soft The function of turning off, which in turn enables the capacitor to be fabricated as an integrated circuit and built in

Inside the chip, and can eliminate the audio noise generated in the capacitor during the low frequency operation of the pulse width modulation signal in the circuit; therefore, the controllable soft start and soft shutdown of the pulse width modulation function The circuit can be integrated into the interior of the LED driver chip so that the LED driver chip can initiate or end the operation of the LED driver chip via the controllable soft-start and soft-shutdown circuit with pulse width modulation function. When the LED driving chip inputs the pulse width modulation signal externally, the controllable soft start and soft closing circuit with the pulse width modulation function can make the external circuit input under the feedback function of the entire wafer circuit. The feedback terminal voltage is proportional to the Duty Cycle of the pulse width modulation signal, thereby realizing the adjustment of the brightness of the (10) brightness by the pulse width dependence; therefore, by the pulse width Wei The use of the controllable soft-opening soft-off circuit effectively simplifies the internal circuit structure of the LED driver chip, thereby making the application of the relevant periphery simpler and requiring fewer peripheral components and lower cost. A controllable soft start and soft shutdown circuit with pulse width modulation function includes: - operation transduction amplifier, - first resistance, - second resistance, a first switch, a third switch, a The fourth switch, a first reverse 7 201014183 phase device, a second inverter, a controllable start timer, an RC network - a reference voltage source and a pulse width modulation signal input terminal, a feedback a voltage input end and a switch circuit output end; the first switch is connected in parallel with the second resistor, and the first switch is connected to one end of the parallel circuit formed by the first resistor to be connected in parallel with the inverting input end of the operational transconductance amplifier The other end of the loop is connected to the feedback voltage input terminal; the second switch is connected in series with the first resistor, and the other end of the second switch is connected to the positive phase input terminal of the operational transconductance amplifier, the first resistor The other end is connected to the inverting input terminal of the operational transconductance amplifier; one of the third switches is terminated to the positive phase input terminal of the operational transconductance amplifier, and the other end of the third switch is connected to the ground end; One of the four switches is terminated Calculating a positive phase input terminal of the transconductance amplifier, and the other end of the fourth switch is connected to a positive end of the reference voltage source; and the team network is connected between the output end of the operational transconductance amplifier and the ground end, And the output end of the operational transduction amplifier is connected to the output end of the switch circuit; the pulse width modulation signal input end is respectively connected to the input end of the first inverter, the control end of the fourth switch, and the Controlling the input end of the timer; wherein the output of the first inverter is connected to the control end of the third switch, and the output of the controllable start timer is respectively connected to the second The input end of the inverter is connected to the control end of the first switch, and the output end of the second inverter is connected to the control end of the second switch. Further, the reviewing committee can have a further understanding of the technical features of the present invention. The following is a detailed description of the three specific embodiments and the drawings. 8 201014183 [Embodiment] Embodiment 1 'Please refer to the fifth, sixth to twelfth and fifteenth to seventeenth views. The present invention is a controllable soft start and soft with pulse width modulation function. The circuit (1) is closed, comprising: an operational transconductance amplifier (11), a first resistor (161), a second resistor (162), a first switch (151), a second switch (152), and a a third switch (153), a fourth switch (154), a first © inverter (141), a second inverter (142), a controllable start timer (13), an RC network The circuit, a reference voltage source (12) and a pulse width modulation signal input terminal (181), a feedback voltage input terminal (182) and a switching circuit output terminal (183). Wherein the first switch (ι 51), the second switch (152), the third switch (153) and the fourth switch (154) both use a field effect transistor, and in practical applications, a double can also be used. The carrier transistor; the reference voltage source (12) is a bandgap reference voltage source', and in practice, a voltage divider circuit with a bandgap φ reference voltage source can also be used. The first switch (151) is connected in parallel with the second resistor (162), and one of the parallel loops formed by the first switch (151) and the second resistor (162) is terminated opposite to the operational transconductance amplifier (11). a phase input end, the other end of the parallel circuit is connected to the feedback voltage input terminal (182); the second switch (152) is connected in series with the first resistor (161), and the other end of the second switch U52) Connected to the non-inverting input terminal of the operational transconductance amplifier (11), the other end of the first resistor is connected to the inverting input terminal of the operational transconductance amplifier (11); the third switch (153) is 9 201014183 - terminal Connected to the positive phase input terminal of the operational transconductance amplifier (1), the other end of the third_(153) is connected to the ground terminal; one of the fourth _〇54) is terminated to the different transconductance amplifier (1)) The positive phase is input to the human terminal, and the fourth terminal (the other end of the 1(4) is connected to the positive terminal of the scale f source (12); * between the output of the operational transconductance amplifier (11) and the ground terminal The network is connected, and the output of the operational transconductance amplifier (11) is connected to the output of the switch circuit (183), wherein the rc network is using a resistor (171) and The other end of the capacitor (172) is formed of a series RC network 'and the resistor (171) is connected to that of the operational transconductance amplifier (11) of the output terminal, the capacitive 〇72) of the other end is connected to the ground terminal. The pulse width modulation signal input terminal (181) is respectively connected to an input end of the first inverter (141), a control end of the fourth switch (154), and the controllable start timer (13) The input end of the first inverter (141) is connected to the control end of the third switch (153), and the output ends of the controllable start timer (13) are respectively connected to The input end of the second inverter (142) and the control end of the first switch (151), and the output end of the second inverter (142) is connected to the control of the second switch 〇 52) end. The pulse width modulation signal (19) of the pulse width modulation signal input terminal (181) controls opening or closing of the fourth switch (154), and controls the first via the first inverter (141) Opening or closing of the three switch (153); the controllable start timer (13) is for detecting the time when the pulse width modulation signal (19) is high or low, and controlling the first switch ( 151) is opened or closed 201014183, and the second switch (152) is controlled to open or close via the second inverter (142). When the pulse width modulation signal (19) of the pulse width modulation signal input terminal (181) is at a high potential, the fourth switch (154) is closed, and the first inverter (141) is The third switch (153) is turned on; when the pulse width modulation signal (19) of the pulse width modulation signal input terminal (181) is low, the fourth switch (154) is turned on and The first inverter (141) is such that the third switch (153) is closed. When the pulse width modulation signal input terminal (181) of the pulse width modulation signal input terminal (181) is at a high potential or a low potential for a time longer than a preset time, the controllable start timer (13) outputs a potential causes the first switch (151) to be closed, and the second switch (152) is turned on via the second inverter (142); the pulse width modulation of the pulse width modulation signal input terminal (181) When the variable signal (19) is at a high potential or a low potential for less than a preset time, the controllable start timer (13) outputs a potential to turn on the first switch (151), and via the second reverse The phaser (142) is such that the second switch (152) is closed. The controllable soft start and soft-off circuit (1) with pulse width modulation function has four working states: wherein 圮 is the resistance of the first resistor (161); and 2 is the second resistor ( 162) resistance value; Gm is the transduction of the operational transconductance amplifier (11); the reference voltage is the output voltage of the reference voltage source (12); back to 201014183, the voltage is the voltage of the feedback voltage input terminal (182) . The first working state is the working state (1), and its equivalent circuit is as shown in Fig. 8: wherein the input voltage is the positive phase input terminal and the inverting input terminal of the operational transconductance amplifier (11). The voltage at both ends; the output current /0/ is the output current of the operational transconductance amplifier (11). When the pulse width modulation signal (19) input by the controllable soft start and the soft-closed electric Φ circuit (1) with the pulse width modulation function is high, and the pulse width modulation signal (19) The time for the high potential is less than the preset controllable start-up time. Then, the input voltage of the operational transconductance amplifier (11) is: ~: Shaoqing-VFB)x-5-R, +Rl (1) and the output current of the operational transconductance amplifier (11) / (7) for:

Ο 7〇« = Gm-vn=Gmx (ymF ^vfb)x __L R'+R^ (2) In the operating state (1), the output current of the operational transconductance amplifier (8) is the capacitance (172) ) to charge. The second working state is the working state (2), and its equivalent circuit is as shown in the ninth figure: wherein the input motor is the positive phase wheel input end and the reverse phase input end of the operational transduction amplifier (11) The voltage at both ends; the output current ^ is the output current of the 12121414 different transconductance amplifier (11). When the pulse width modulation signal (19) of the controllable soft start and soft-off circuit (1) with the pulse width modulation function is high, the pulse width is changed to 5 ( 19) The time for the south potential is greater than the preset controllable start-up time.

Then, the input voltage of the operational transconductance amplifier (11) is: K2 = VreF-vfb (3) and the output current / 〇2 of the operational transconductance amplifier (11) is: I〇2=^-K2 =Gmx(VR£F-FFg).. (4) The first working state, that is, the working state (3), the equivalent circuit is as shown in the tenth figure. The input voltage 6 is the operational transconductance amplifier (n ) the right phase

The voltage across the input and inverting inputs; the output current is the output current of the operational amplifier (11). When the pulse width is light, the controllable soft-opening soft-close circuit (1) converts the pulse width of the human (10) to a low potential, and the pulse width modulation (10) is a low potential _ less than the Wei mosquito. Controlled startup time. At this time, the input voltage of the operation transduction amplification H(1)) is: 13 201014183 Equation (5) Then the operational current of the operational transconductance amplifier (1) is ... (6) and in the case of work sorrow (2) The operation of the (6) towel of the operational transconductance amplifier ((1) the output current is - negative value means that the capacitance (172) is in the discharge state at this time, the path is reversed from the capacitance 〇 72) to the operational transduction amplification The output of H(ll), therefore, the discharge current of the capacitor (172) is the output current of the operational transconductance amplifier (11). The fourth working state, that is, the working state (8), its equivalent circuit is as shown in the tenth-figure: where the input voltage 6 is the two ends of the positive-phase input terminal and the inverting input terminal of the operational transduction amplifier ((1) Voltage; output current 7 ~ is the output current of the operational transconductance amplifier (11). When the pulse width modulation function is controlled by the soft-start and soft-close circuit (1) The signal (19) is low, and the pulse-wave modulation signal (19) is low for a longer time than the preset controllable start-up time. At this time, the input voltage of the operational transconductance amplifier (11) is:

V^=-VFBX ^1+^2 .. Equation (7) 201014183 The output current of the operational transconductance amplifier (1) is: (8) and in the working state (4), in equation (8) The operating current of the operational transconductance amplifier (n) is a negative value, that is, the capacitance (172) is in a discharging state at this time, and the discharging current path is reversely flown by the capacitor (172) into the operation. The output of the amplifier (11), therefore, the discharge current of the capacitor (172) is the output current of the operational transconductance amplifier (11). Please refer to the sixth figure, the embodiment of the present invention applied to the LED driving chip; the enabling end (EN) of the LED driving chip (2) is input to the pulse width modulation signal CPfFM) by the external connection circuit, and then The enabling circuit (21) inside the LED driving chip (2) inputs the pulse width modulation signal (19) to the controllable soft start and soft-close circuit (丨) of the pulse width modulation function. The wave width modulation signal input terminal (181); and the feedback terminal (FB) of the LED driver chip (2) is input by the external connection circuit, and the feedback voltage is directly input to the pulse width. The feedback voltage input end (182) of the controllable soft start and soft turn off circuit of the modulation function; and the switch circuit of the controllable soft start circuit (1) with the pulse width modulation function The output terminal (183) is an input terminal connected to the pulse width modulation comparator (221) input to the LED driving chip (2). Wherein, the output voltage G is the controllable type of the pulse width modulation function 15 201014183 soft start and soft turn off circuit (1) of the operational transconductance amplifier (1)) of the wheel terminal voltage; the reference voltage ^ is the pulse width The control voltage source of the controllable soft start and soft shutdown circuit (1) of Wei (the output voltage of (2); the voltage of the output voltage of the external connection circuit of the LED driver chip (2), feedback The voltage ^^ is 〇: 0 drives the feedback terminal (FB) voltage of the chip (2), and is also the feedback voltage input terminal of the controllable soft start and soft-off circuit G) with pulse width modulation function (182) voltage. When the LED driving chip (2) is activated, the pulse width modulation of the pulse width modulation signal input terminal (181) of the controllable soft start and soft-close circuit (1) with pulse width modulation function The signal (19) is high, and the output of the controllable δ-timer (13) is low; therefore, the controllable soft-start and soft-off circuit with pulse width modulation function (1) Is in working condition (1). The output voltage of the operational transconductance amplifier (11) is connected to the pulse width modulation by the switchable circuit output terminal (183) of the controllable soft start and soft-close circuit with the pulse width modulation function. The input of the device (221) passes through the RS flip-flop (23) and the power driving module (24), thereby generating a driving signal of the power transistor (25), thereby turning on the power transistor (25). The output current of the operational transconductance amplifier (11) is to charge the capacitor (172), so that the output voltage of the operational transconductance amplifier (11) begins to rise gradually; with the operation of the transconductance amplifier (11) As the voltage of the wheel rises, the power transistor (25) starts to operate. 201014183 By the theory of the circuit diagram of the sixth figure and the related theory of the switching power supply, it can be known that the output voltage of the external connection circuit starts to rise, the current on the resistor (3) gradually increases, and the LE:D drive wafer ( 2) The feedback voltage ^^ increases in proportion to the output voltage of the external connection circuit until the feedback voltage and the reference voltage of the controllable soft-start and soft-off circuit (1) with the pulse width modulation function The output reference voltage of source (12) is equal. It can be seen from equation (2) that the output current /0/ of the operational transconductance amplifier (11) is twice the output current of the conventional controllable soft-start circuit compared to the conventional controllable soft-start circuit. In order to achieve the same output voltage rise speed, the capacitance value of the capacitor (172) in the controllable soft start and soft-shutdown circuit (1) with pulse width modulation function is only the formula. The capacitance value of the controllable soft-start circuit is &/ (and times the capacitance value required in the original circuit is reduced. When the enable terminal (EN) of the LED driver chip (2) is input to the pulse wave by the external connection circuit When the width modulation signal (ΡΚΛ/) continues to be high for more than the preset controllable start-up time, the controllable soft-start and soft-off circuit (1) with the pulse width modulation function The controllable start timer (13) outputs the zeta potential, so that the controllable soft start and soft-close circuit (1) with the pulse width modulation function enters the working state (2). Then the LED drive chip (2) The feedback voltage is clamped to the voltage equivalent of the output reference voltage of the quasi-voltage source (12) of the controllable soft-start and soft-off circuit (丨) with the pulse width modulation function. When the enable terminal (EN) of the LED driver chip (2) is connected by an external circuit When the input pulse width modulation signal changes from a high potential to a low potential, the controllable soft start of the pulse width modulation function and the controllable start timer (13) of the soft shutdown circuit output a high potential. Further, the controllable soft start and soft-off circuit (丨) with the pulse width modulation function enters the working state (3), and the output voltage 4 of the operational transconductance amplifier (11) is via the pulse width. The switchable circuit output (183) of the programmable soft start and soft-shutdown circuit G) is coupled to the input of the pulse width modulation comparator (221) and passes through the RS flip-flop (23) and power The driving module (24) further generates a driving signal of the power transistor (25). At this time, the capacitor (172) is in a discharging state, and the magnitude of the discharging current is the output current J(7) of the operational transconductance amplifier (11) in the equation (6); and when the output of the operational transconductance amplifier (11) When the voltage 匕 is gradually reduced, the operating time of each cycle of the power transistor (25) is indirectly reduced until the power transistor (25) is completely turned off. It can be seen from equation (6) that the discharge current of the capacitor (172) is the output current of the operational transconductance amplifier (11) compared with the controllable soft-start circuit of the conventional formula. The soft start circuit is doubled. In order to achieve the same output voltage drop speed, the capacitor required for the pulse width modulation function and the capacitor (IK) in the soft-start circuit and soft-close circuit (1) 201014183 The value is only twice the capacitance of the controllable soft-start circuit of the conventional method, and reduces the capacitance value required in the original circuit. When the enable terminal (EN) of the LED driver chip (2) is input from the external connection circuit When the wave width modulation signal (the corpse fTM) continues to be low for more than a preset controllable start-up time, the controllable soft start and soft-off circuit (1) with the pulse width modulation function The controllable start timer (13) outputs a high potential, so that the controllable soft start and soft-close circuit (1) with the pulse width modulation function enters the working state (4). Then the LED drive chip (2) The feedback voltage F/τβ will be clamped to the voltage value of zero potential When the enable terminal (EN) of the LED driver chip (2) is input to the pulse width modulation signal (PPFM) as shown in Fig. 12 by the external connection circuit, the pulse width modulation signal (P gray M) is used. The period of the control is usually much smaller than the preset controllable start-up time'. The controllable soft start circuit with the pulse width modulation function and the soft start circuit (1) have the output of the controllable start timer (13). Potential; at this time, the working state of the controllable soft-start and soft-off circuit (1) with the pulse width modulation function will be periodically converted between the working state (1) and the working state (3). And the switching frequency is the same as the frequency of the pulse width modulation signal (ΡπΜ). When the circuit is stable and reaches the dynamic balance, the operation of the controllable soft start and soft-off circuit (1) with the pulse width modulation function The average voltage of the output voltage of the transconductance amplifier 19 201014183 (Η), the feedback voltage of the LED driver chip (2), and the output of the external connection circuit are unchanged, and the average charge on the capacitor (172) Keep unchanged, and then you can get the following equation, where Duty Cycle D is the duty cycle of the pulse width modulation signal (household gray):

Vfb=DxVref (9) From equation (9), the feedback voltage of the LED driver chip (2) drives the enable (EN) of the chip (2) to be pulse-width modulated (PifM) input from the external connection circuit. The duty cycle is proportional. Embodiments - A clear view of the thirteenth, sixth to nineth and fifteenth to seventeenth, the present invention is a controllable soft start and soft turn off circuit with pulse width modulation function (1) The method includes: an operational transconductance amplifier (11), a first-resistor (161), a second resistor (162), a first switch (151), a second switch (152), and a second inverter. (142), a controllable start timer (13), an RC network, a reference voltage source (12) and a pulse width modulation signal input terminal (181), and a feedback voltage input terminal (182) And a switching circuit output terminal (183); wherein the first switch (151) and the second switch (152) both use field effect transistors, and in practical applications, a bipolar transistor can also be used; The reference voltage source (12) is a voltage-gap reference voltage source, and in actual use 20 201014183 can also be used as a voltage divider circuit. The first switch (151) is connected in parallel with the second resistor (10)), and one of the parallel loops formed by the first switch (151) and the second resistor (10) is terminated to the inverting end of the guide The other end of the parallel circuit is connected to the feedback voltage input terminal (182); the first item (10) is connected in series with the first resistor (161) and the other end of the second switch (152) is respectively connected To the positive terminal of the operational amplifier ϋ (11) and the positive terminal of the reference voltage source (10), the other end of the first resistor (161) is difficult to operate the inverting input of the transconductance amplifier (1). The output of the operational transconductance amplifier (11) is connected to the output of the switching circuit (183); The network is formed by using a resistor (171) and a valley (172) in series, and the other end of the resistor (171) is connected to the output of the operational transconductance amplifier (11). The other end of the capacitor (172) is connected to the ground. The pulse width modulation signal input terminal (181) is connected to the input end of the controllable start timer (13); the output end of the controllable start timer (丨3) is respectively connected to the first The input end of the second inverter (142) and the control end of the first switch (151), and the output end of the second inverter (丨42) is connected to the control end of the second switch (152) . The controllable start timer (13) is used to detect the time when the pulse width modulation signal (19) is high or low, and controls the opening or closing of the first switch (1, 51, 51,183,183) The opening or closing of the second switch (152) is controlled via the second inverter (142). When the pulse width modulation signal input terminal (181) of the pulse width modulation signal input terminal (181) is at a high potential or a low potential for a time longer than a preset time, the controllable start timer (13) outputs a high potential causes the first switch (151) to be closed, and the second switch (152) is turned on via the second inverter (142); the pulse width of the pulse width modulation signal input terminal (181) When the width modulation k number (19) is high or low for less than the preset time, the controllable start timer (13) outputs a low potential to turn the first switch (151) on. The second switch (152) is closed via the second inverter (142). The controllable soft start and soft-off circuit a) having the pulse width modulation function has two working states: wherein 圮 is the resistance of the first resistor (161); A is the third resistor (162) The resistance value is (9) is the transduction of the operational transconductance amplifier (1); the reference voltage is the output voltage of the reference voltage source (12); and the feedback voltage is the voltage of the feedback voltage input terminal (182). The first working state, that is, the working state (1), its equivalent circuit is as shown in the eighth figure: wherein the input voltage ^" is the operational transconductance amplifier ((1), the phase wheel input end and the inverting input end two Terminal voltage; input (four) current ~ is the output current of the operational transconductance amplifier (11); 曰 " Hai with pulse width modulation function of the controllable soft start and soft shutdown 22 201014183 road (1) input pulse The wave width modulation signal (19) is high, and the pulse width modulation signal (19) is at a high potential for less than a preset controllable start-up time. & At this time, the operational transconductance amplifier (11) The input voltage is .. formula (1)

And the output current /0/ of the operational transconductance amplifier (11) is · 701 = Gm - Vn = Gm X (V^ - rra) x Ά (2). In the operating state (1), the operational transconductance amplifier (10) The output current Λ?/ is to charge the capacitor (172).

+ Τ? 2 The second working state, ie working state (2), its equivalent circuit is shown in Figure IX: where the input voltage 6 is the non-inverting input and inverting phase of the operational transconductance amplifier (11) The voltage across the input terminal; the output current / 〇2 is the output current of the operational transconductance amplifier (11): when the controllable soft start and soft-close circuit (1) with pulse width modulation function is input The pulse width modulation signal (19) is high, and the pulse width "cycle" k (19) is the south potential for a time greater than a preset controllable startup time. 23 201014183 At this time, the input voltage κί2 of the operational transconductance amplifier (11) is: V'2=VREF~VFB (3) and the output current/cut of the nasal transduction amplifier (11) is: Equation (4) I02 = Gm · Vi2 = GM X - VF8) Please refer to the sixth figure, the embodiment of the present invention applied to the LED driving chip; the enabling end (EN) of the LED driving chip (2) is external After connecting the circuit to the pulse width modulation signal (cadence FM), the pulse width modulation signal (19) is input to the pulse width through the internal enabling circuit (21) of the LED driving chip (2). The pulse width modulation signal input terminal (181) of the controllable soft start and soft turn off circuit of the modulation function (1), and the feedback terminal (FB) of the LED drive chip (2) is connected by an external circuit After inputting the feedback voltage, the feedback voltage is directly input to the feedback voltage input terminal (182) of the controllable soft start and soft-off circuit (1) having the pulse width modulation function; Wave width modulation function The controllable soft start and soft shutdown circuit (1) of the switch circuit output (183) is connected to the LED drive chip (2) Pulse width modulation comparators (221) one of the inputs. Wherein, the output voltage is the output voltage of the operational soft-start and soft-shutdown circuit (1) of the operational transconductance amplifier (U); the reference voltage is the pulse width modulation Functionally controlled soft-start and soft-off circuit (1) The output voltage of the reference voltage source (12); output 24 201014183 Voltage is the output terminal of the external connection circuit of the LED driver chip (2); The feedback terminal (10) of the factory's z^LED driver chip (2) is also the feedback voltage input terminal (182) of the controllable soft-start and soft-off circuit (1) with pulse width modulation function. The voltage. When the LED driving chip (2) is activated, the pulse width modulation of the pulse width modulation signal input terminal (181) of the controllable soft start and soft-close circuit (1) with pulse width modulation function The signal (19) is high, and the output of the controllable starter (13) is low; therefore, the controllable soft start and soft-shutdown circuit with the pulse width modulation function (D is at Working state (1) The output voltage G of the operational transconductance amplifier (11) is the output of the switching circuit via the controllable soft-start and soft-shutdown circuit (1) with pulse width modulation function (183). ) to connect to the input of the pulse width modulation comparator (221), and through the RS flip-flop (23) and the power drive module (24), thereby generating a driving signal of the power transistor (25), thereby turning on the power Crystal (25). The output current / 〇 / of the operational transconductance amplifier (11) is to charge the capacitor (172), so that the output voltage of the operational transconductance amplifier (丨丨) begins to rise gradually; The operation of the operational amplifier (Π) is the rise of the output voltage core 'power transistor ( 25) Then the action starts. However, according to the theory of the circuit structure of the sixth figure and the related theory of the switching power supply, the output voltage of the external connection circuit starts to rise, and the current on the resistor (3) gradually increases, and the LED drives the chip. (2) The feedback voltage is proportional to the output voltage κ0ί/Γ of the connection circuit of 201014183, until the feedback voltage and the controllable soft-start and soft-off circuit with the pulse width modulation function (1) The output voltage reference voltage of the reference voltage source (12) is equal to 2. According to equation (2), the output current of the operational transconductance amplifier (11) is compared with the controllable soft start circuit of the conventional formula. / is the output current of the controllable soft-start circuit of 习 / (/? / + / ? 2) times. In order to achieve the same output voltage rise speed ' then the pulse width modulation function can be The capacitance required for the capacitor (172) in the soft-start and soft-close circuit (1) is only 圮/(8) times the capacitance value of the controllable soft-start circuit of the conventional type, and the original circuit is reduced. The required capacitance value. When the enable terminal (EN) of the LED driver chip (2) is input to the pulse width modulation signal (PWM) by the external connection circuit and continues to be high for more than a preset controllable start-up time, then the pulse The controllable soft start of the wave width modulation function and the soft start circuit (1) of the controllable start timer (13) output a high potential, thereby enabling the controllable soft start of the pulse width modulation function And the soft shutdown circuit (1) enters the working state (2). The feedback voltage of the LED driver chip (2) is clamped to the output reference voltage factory of the reference voltage source (12) of the controllable soft-start and soft-off circuit (1) with the pulse width modulation function. ^ Equal voltage value. Embodiment 2 'Please refer to the fourteenth, sixth to eighth, tenth, twelfth and fifteenth to seventeenth drawings. 'The present invention is a controllable function with pulse width modulation 26 201014183 The soft start and soft turn off circuit comprises: an operational transconductance amplifier (11), a first resistor (161), a second resistor (162), a third switch (153), and a fourth switch (154) a first inverter (141), an rc network, a reference voltage source (丨2) and a pulse width modulation signal input terminal (181), a feedback voltage input terminal (182) and a switch a circuit output terminal (183); wherein the third switch (153) and the fourth switch (154) both use field effect transistors, and in practical applications, a bipolar transistor can also be used; the reference voltage source (12) is to use a bandgap reference voltage source, and in practice, a voltage divider circuit with a bandgap reference voltage source can also be used. One of the second resistors (162) is terminated to the inverting input of the operational transconductance amplifier (丨丨), and the other end of the second resistor (162) is coupled to the feedback voltage input terminal (182); One of the first resistors (161) is terminated to the inverting input terminal of the operational transconductance amplifier (11), and the other end of the first resistor (161) is connected to the non-inverting input terminal of the operational transconductance amplifier (11); One of the third switch (153) is terminated to the non-inverting input of the operational transconductance amplifier (11), and the other end of the third switch (153) is connected to the ground end; one end of the fourth switch (154) Connected to the non-inverting input of the operational transconductance amplifier (11), and the other end of the fourth switch (154) is connected to the positive terminal of the reference voltage source (12); and the output of the operational transconductance amplifier (11) The RC network is connected between the terminal and the ground, and the output of the operational transconductance amplifier (11) is connected to the output of the switch circuit (183); wherein the RC network uses a resistor (171). ) is connected to a capacitor (172) in the form of a 27 201014183 RC network, and the other end of the resistor (17 i) is connected to the operational transduction At the output of the amplifier (11), the other end of the capacitor (172) is connected to the ground. - the pulse width modulation signal input terminal (181) is respectively connected to an input end of the first inverter (141) and a control terminal of the fourth switch (154); wherein the first inverter ( The output of 141) is connected to the control terminal of the third switch (153). The pulse width modulation signal (19) of the pulse width modulation signal input terminal (181) controls opening or closing of the fourth switch (154), and controls the first via the first inverter (141) The three switches (153) are opened or closed. When the pulse width modulation signal (19) of the pulse width modulation signal input terminal (181) is at the south potential, the fourth switch (154) is closed, and the first inverter (141) is The third switch (153) is turned on; when the pulse width modulation signal (19) of the pulse width modulation signal input terminal (181) is low, the fourth switch (154) is turned on and The first inverter (141) © causes the third switch (153) to close. The controllable soft start and soft-off circuit (1) with pulse width modulation function has two working states: wherein A is the resistance of the first resistor (161); 圮 is the second resistor (162) The resistance value of the transconductance amplifier (u); the reference voltage K-shaped F is the output voltage of the reference voltage source (12); the feedback voltage is the feedback voltage input terminal (182) Voltage. The first working state, that is, the working state (1), its equivalent circuit is as shown in the eighth diagram of the 28th 201014183: wherein the input voltage 匕 is the positive phase input terminal and the reverse phase input of the operational transconductance amplifier (u) The voltage of the terminal is the output current of the operational transconductance amplifier (11). When the pulse width modulation signal (19) input by the controllable soft start and soft-off circuit (1) with the pulse width modulation function is high, the pulse width modulation signal (19) is high. The potential coffee is less than the preset controllable start-up time. Then, the input voltage of the operational transconductance amplifier (11) is:

Vi\ = (Vref~Kb)x ———

Rl+R2 (1) and the output current of the operational transconductance amplifier (8) is: m % ura) χ '+Rl (Expression (2) and in the operating state (1) 'The operational transconductance amplifier (11) The output current '〇/ is the capacitor (172) is charged. The second working state, that is, the working state (3), the equivalent circuit is as shown in the tenth figure: its towel, the input voltage 6 is the operation The voltage between the non-inverting input terminal and the inverting input terminal of the transconductance amplifier (11); the output current 7 is still the output current of the transconductance transconductance amplifier (11). When the pulse width modulation function is used Controllable soft start and soft power off 29 201014183 The pulse width modulation signal (19) input by the road (1) is low, and the pulse width modulation Wei (10) is low (four), _ first set controllable Start-up time. At this time, the input voltage of the (four) lead amplifier (8) is ^+r2

Vi3=~Vfbx (5) ❹ The output current / 〇3 of the operational transconductance amplifier (11) is J〇3^Gm-Vi3=-GmxVFB:

Rl+R^ (6) In the working state (3), the output current of the operational transconductance amplifier (11) in the equation (6) is a negative value, that is, the capacitance (172) is at this time. Is in a discharged state' and the discharge current path is reversely flown from the capacitor (172) into the output of the operational transconductance amplifier (11). Therefore, the discharge current of the capacitor (172) is the operational transconductance amplifier (11). ) The output current. Please refer to the sixth embodiment of the present invention for applying the LED driver chip. The enable terminal (EN) of the LED driver chip (2) is input from the external connection circuit to input the pulse width modulation signal (iWM). Transmitting the pulse width modulation signal (19) to the controllable soft start and soft shutdown circuit (1) with the pulse width modulation function via the enable circuit (21) inside the LED driver chip (2) The pulse width modulation signal input terminal (181); and the feedback terminal 201014183 (FB) of the LED driver chip (2) is input directly from the external connection circuit to directly input the feedback voltage to the pulse money. The feedback voltage input terminal (182) of Wei's controllable money start-up and soft-off circuit (1); and the controllable soft start and soft-off circuit (1) with pulse width modulation function The circuit output (183) is one of the inputs connected to the pulse width modulation comparison |§ (221) of the input to the LE:D driver chip (2). Wherein, the output voltage G is the output voltage of the controllable soft start of the pulse width modulation function and the operation of the soft turn-off circuit (1) (the operational transconductance amplifier 〇丨); the reference voltage ^ dirty is the pulse wave The controllable soft start of the width modulation function and the output voltage of the reference voltage source (12) of the soft-off circuit (1); the output voltage is the output voltage of the external connection circuit of the LED driver chip (2); the feedback voltage b is the feedback terminal (FB) voltage of the LED driver chip (2), and is also the feedback voltage input terminal (182) of the controllable soft start and soft shutdown circuit (168) with pulse width modulation function. The voltage. When the LED driving chip (2) is activated, the pulse width modulation of the pulse width modulation signal input terminal (181) of the controllable soft start and soft-close circuit (1) with pulse width modulation function The signal (19) is at a high potential, and the output of the controllable start timer (13) is low; therefore, the controllable soft start and soft-off circuit (1) with the pulse width modulation function is at Working status (1). The output voltage of the nasal transduction amplifier (11) is connected to the switch output 31 (183) of the controllable soft start and soft-close circuit (1) with the pulse width modulation function. The pulse width modulation comparator (221) inputs 'and passes through the RS flip-flop (23) and the power drive module (24), thereby generating a driving signal of the power transistor (25), thereby turning on the power transistor (25) . The output current /0/ of the operational transconductance amplifier (11) charges the capacitor (172), so that the output voltage of the operational transconductance amplifier (11) begins to rise gradually; with the operation of the transconductance amplifier ( 11) The output voltage core rises and the power transistor (25) starts to operate. According to the correlation between the circuit structure of the sixth figure and the conventional switching power supply, the output voltage of the external connection circuit starts to rise, the current on the resistor (3) gradually increases, and the LED drive chip (2) is fed back. The voltage rises in proportion to the output voltage of the externally connected circuit, ot/r, until the voltage source and the controllable soft-start and soft-close circuit (1) of the pulse width modulation function are referenced ( 12) The output reference voltage is equal to each other. It can be seen from equation (2) that the output current / 〇 / of the operational transconductance amplifier (11) is twice the output current of the conventional controllable soft-start circuit compared to the conventional controllable soft-start circuit. In order to achieve the same output voltage rise speed, the capacitance value of the capacitor (172) in the controllable soft start and soft-shutdown circuit (1) with pulse width modulation function is only the formula. The capacitance value of the controllable soft-start circuit is 圮/(Λ/+/ω times, and the capacitance value required in the original circuit is reduced. When the enable terminal (ΕΝ) of the LED driver chip (2) is connected by an external circuit Input 32 201014183 When the pulse width modulation signal CPfFA/) changes from high potential to low potential, the controllable soft start and soft shutdown circuit with pulse width modulation function (the controllable start timer of U) 13) The output high potential, so that the controllable soft start and soft-close circuit (丨) with the pulse width modulation function enters the working state (3). The output voltage of the operational transconductance amplifier (11) is The switch circuit output terminal (183) via the controllable soft start and soft-shutdown circuit of the pulse width modulation function is coupled to the input of the pulse width modulation comparator (221) and is triggered by the RS. (23) and the power drive module (24), thereby generating work Crystal electrical drive signal (25) of. At this time, the capacitor (172) is in a discharged state, and the discharge current is the output current /OJ of the operational transconductance amplifier (11) in the equation (6); and when the operational transconductance amplifier (11) When the output voltage 匕 is gradually reduced, the operating time of each cycle of the power transistor (25) is indirectly reduced until the power transistor (25) is completely turned off. It can be seen from equation (6) that compared with the controllable soft-start circuit of the conventional mode, the discharge f-flow of the electric valley (172) is the output current k of the operation liberation |||(11) is a custom The controlled soft start circuit (8) says) times. In order to achieve the same output voltage drop speed, the controllable soft start and soft-off circuit with pulse width modulation function (1) the capacitance required for the capacitor (172) is large, and is only a customary formula. The capacitance value of the controlled soft-start circuit and / / (A + D times ' reduce the capacitance value required for the original circuit board. 33 201014183 When the enable terminal (εν) of the LED driver chip (2) is input by an external connection circuit As shown in the twelfth figure, the pulse width modulation signal CP stage Μ), since the period of the pulse width modulation signal (PFM) is usually much smaller than the preset controllable start time 'the pulse width The controllable soft start of the modulation function and the soft start circuit (1) of the controllable start timer (13) output low potential; at this time, the controllable soft start with the pulse width modulation function and The working state of the soft-off circuit will be periodically converted between the working state (1) and the working state (3), and the switching frequency is the same as the pulse width modulation signal (the frequency of the household ash ^. When the circuit is stable and reaches After dynamic balancing, the controllable softness of the pulse width modulation function The output voltage of the operational transconductance amplifier (11), the feedback voltage of the LED driver chip (2), and the output voltage of the external connection circuit remain unchanged. And the average charge on the capacitor (172) remains unchanged, and thus the equation "Wut the duty cycle (Duty Cycle) D is the duty of the pulse width modulation signal (ρ milk V/)] Ratio: Άν赃... Equation (9) From equation (9), the [ED drive crystal (2) feedback voltage ^ and the [ED drive wafer (2) enable (EN) are modulated by the pulse width of the external connection circuit input. The duty cycle of letter 34 201014183 Cpwm) is proportional. The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Therefore, those skilled in the art can make modifications and changes to the above embodiments without departing from the spirit of the present invention. This creation has the industrial applicability, novelty and progress, and meets the requirements of new patents. [Simple description of the map]

The controllable soft-start circuit diagram of the first figure is used; when the controllable soft-start circuit of the second figure is applied to the LED driver chip, the input frequency of the LED driver chip is ΙΚΗζ, the duty ratio Is a pulse width modulation signal of 1〇〇/0; >_, voltage waveform of the output terminal voltage of the LED driver chip and the output voltage of the external connection circuit of the LED driver chip (1); When the controllable soft-start circuit of the three-picture mode is applied to the LED driver chip, the input frequency of the LED driver chip is ΙΚΗζ, the duty ratio is 40%, and the pulse width modulation signal is _, LED The voltage waveform of the output voltage of the external connection circuit of the driving chip and the voltage of the output voltage of the external connection circuit of the driving chip (2); the application of the controllable soft-start circuit of the fourth figure to the LED When the chip is driven, the frequency input to the enable terminal of the LED driver chip is 35 201014183 脉 the pulse width modulation signal of 80% of the work ratio, the feedback terminal voltage of the LED driver chip, and the external connection circuit of the LED driver chip Voltage waveform of the output voltage vour ( FIG. 5 is a circuit diagram of the present invention (a); FIG. 6 is a diagram showing an embodiment of the present invention applied to an LED driver chip; FIG. 7 is an external application circuit diagram of the LED driver chip; 1) equivalent circuit diagram; ninth diagram equivalent circuit diagram of the working state (2) of the present invention; eleventh diagram equivalent circuit diagram of the working state (3) of the present invention; eleventh diagram working state of the invention (four Equivalent circuit diagram of Fig. 12; waveform diagram of the pulse width modulation signal of the twelfth figure; Fig. 13 is a circuit diagram of the invention (2); Fig. 14 is a circuit diagram of the invention (3); When the LED driving crystal# of the present invention is applied, the frequency of the input end of the LED driving chip is IKJ^Z, the pulse width modulation signal of the duty ratio is 10〇/〇, and the LED driving chip is used. Voltage waveform diagram of the output terminal voltage VOUT of the external connection circuit of the feedback voltage driving chip (1)·, FIG. 16 is applied to the LE:D driving chip of the present invention, and the input terminal of the LED driving chip is input. The frequency is ΙΚΗζ, the duty ratio is 4〇0/〇36 201014183 Pulse wave width modulation signal household _, LED driver chip feedback terminal voltage and LED driver chip external connection circuit output terminal voltage \/0177 · voltage waveform diagram (two;); When the LED is driven by the chip, the input frequency of the LED driver chip is 1Kpjz, the pulse width modulation signal/WW of the duty ratio is 8〇%, and the feedback of the driving chip is external to the 4 voltage driving chip. The voltage waveform of the output voltage of the connected circuit is (0). [Main component symbol description] (I) Controllable soft-start and soft-off circuit with pulse width modulation function (II) Operational transduction amplifier (12) Reference voltage source (13) Controllable start timer (141) First inverter (142) second inverter (151) first switch (152) second switch (153) third switch (154) fourth switch (161) first resistor (162) second resistor 37 201014183 (171) Resistor (172) Capacitance. (181) Pulse Width Modulation Signal Input (182) Feedback Voltage Input (183) Switch Circuit Output (19) Pulse Width Modulation Signal (2) LED Driver chip

A ^ (21) enable circuit (221) (222) comparator (23) RS flip-flop (24) power drive module (25) power transistor (26) oscillating circuit (27) slope conversion circuit ❹ (3) Resistor (4) Controllable soft start circuit Pulse width modulation signal (L) Low potential (Η) High potential (R) RS trigger input (5) RS flip-flop input 38 201014183 (Q)RS Output of the Trigger (IN) LED Driver Chip Input (OUT) LED Driver Chip Output (LX) LED Driver Chip Inductor Terminal (FB) LED Driver Wafer Feedback Terminal (EN) LED Driver Chip The terminal (GND) of the LED driver chip (VIN) The input voltage of the external connection circuit of the LED driver chip; (the output voltage of the external connection circuit of the LED driver chip; (Fra) the feedback terminal of the LED driver chip Voltage

39

Claims (1)

201014183 X. Patent application scope: 1. A controllable soft start and soft shutdown circuit with pulse width modulation function, comprising: an operational transduction amplifier, a first resistor, a second resistor, a first switch a second switch, a third switch, a fourth switch, a first inverter, a second inverter, a controllable start timer, an RC network, a reference voltage source and a pulse a wave width modulation signal input end, a feedback voltage input end and a switch circuit output end; the first switch is connected in parallel with the second resistor, and the first switch is terminated with one of the parallel circuits formed by the second resistor An inverting input terminal of the operational transconductance amplifier, the other end of the parallel circuit is connected to the feedback voltage input terminal; the second switch is connected in series with the first resistor, and the other end of the second switch is connected to the operation transduction a non-inverting input terminal of the amplifier, the other end of the first resistor is connected to an inverting input end of the operational transconductance amplifier; the third switch is terminated to a positive phase input end of the operational transconductance amplifier, and the third The other end of the switch Connected to the ground; the fourth switch is terminated to the positive phase input terminal of the operational transconductance amplifier, and the other end of the fourth switch is connected to the positive terminal of the reference voltage source; and the output of the operational transduction amplifier The rc network is connected between the terminal and the ground, and the output of the operational transduction amplifier is connected to the output of the switch circuit; the pulse width and the signal input end are respectively connected to the money-inverter The wheel end, the control of the fine control_ and the input of the controllable start timer t 201014183, wherein the output end of the 'δ海 first phase ι§ is connected to the control end of the third switch, the controllable The output of the start timer is respectively connected to the input end of the second inverter and the control end of the first switch and the output of the second inverter is connected to the control of the second switch The pulse width modulation signal of the pulse width modulation signal input terminal controls the opening or closing of the fourth switch and controls the opening or closing of the third switch via the first inverter; Controllable start timer is used to detect pulse width Time varying signal is a high potential or low potential, and controlling the opening or closing of the first switch, via the second inverter and controlling the second switch of the open or closed. 2. A controllable soft-start and soft-off circuit with a pulse width modulation function, comprising: an operational transconductance amplifier, a first resistor, a second resistor, a first switch, a second switch, a second inverter, a controllable start timer, a _ Rc network reference voltage source and a pulse width modulation signal input terminal, a feedback voltage input terminal and a switching circuit output terminal; The second resistors are connected in parallel, and the code first-off and the second resistor are formed in parallel, the terminal ends to run a larger H rib input end, and the other end of the parallel circuit is connected to the feedback voltage input end; The second switch is connected in series with the first resistor, and the other end of the second switch is respectively connected to the positive phase of the input device and the positive terminal of the wire quasi-voltage source. The terminal is connected to the inverting input of the operational transconductance amplifier at the end of 201014183; the operational transduction amplifying the round end of the n wheel and the ground end of the rc network, and the output of the operational transduction amplification it is connected to the The output of the compensation circuit; the pulse width modulation is the connection of the controllable An input end of the timer; the output end of the controllable start timer is respectively connected to an input end of the second inverter and a control end of the first switch, and an output end of the second inverter is Is connected to the control end of the second switch; the controllable start timer is used to detect the time when the pulse width modulation signal is high or low, and controls the opening or closing of the first switch, and The opening or closing of the second switch is controlled via the second inverter. 3. A controllable soft start and soft shutdown circuit with a pulse width modulation function, comprising: an operational transduction amplifier, a first resistor, a second resistor, a third switch, a fourth switch, a first inverter, an RC network, a reference voltage source and a pulse width modulation signal input terminal, a feedback voltage input terminal and a switch circuit wheel terminal; one of the second resistors is terminated by the operation The inverting input terminal of the transconductance amplifier is connected to the feedback voltage input terminal; the first resistor is terminated to the inverting input terminal of the operational transconductance amplifier and the first resistor The other end is connected to the non-inverting input terminal of the operational transconductance amplifier; one of the third switches is terminated to the non-inverting input terminal of the operational transconductance amplifier, and the other end of the 42th 201014183 three-switch is connected to the ground end; One of the fourth switches is terminated to the positive phase input of the operational transconductance amplifier, and the other end of the fourth switch is connected to the positive terminal of the reference voltage source; and the output of the operational transduction amplifier is connected to the ground terminal Then the RC network is connected. The output end of the operational transconductance amplifier is connected to the output end of the switch circuit; the pulse width modulation signal input end is respectively connected to the input end of the first inverter and the control end of the fourth switch; wherein The output end of the first inverter is connected to the control end of the third switch; the pulse width modulation signal of the pulse width modulation signal input terminal controls the opening or closing of the fourth switch An inverter controls the opening or closing of the third switch. 4. A controllable soft start and soft-shutdown circuit having a pulse width modulation function according to any one of claims 1 to 3, wherein the circuit is a resistor and a capacitor. An RC network formed in series, and the other end of the resistor is connected to the output of the operational transconductance amplifier, and the other end of the capacitor is connected to the ground, and the reference voltage source is especially a gap reference voltage source Or a voltage divider circuit that passes through a bandgap reference. 5. The controllable soft start and soft-close circuit of the pulse width modulation power cycle b, as recited in claim 1 to 3 of the patent scope, wherein the first switch or the second The switch or the third switch or the fourth switch refers in particular to a dual carrier transistor or a field effect transistor. 43