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Electronic ballast powered by low-voltage sources. Electronic ballast on the KR1211EU1 chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Ballasts for fluorescent lamps

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This version of the power supply from a low-voltage source is an electronic ballast implemented on a specialized microcircuit KR1211EU1.

Chip KR1211EU1 is a specialized controller for electronic ballasts (ballasts) for compact fluorescent lamps powered by an on-board DC network of 3-24 V. Produced using CMOS technology.

In table. 3.12 shows the distinctive characteristics of microcircuits in different cases. The pinout of the cases and the assignment of the conclusions are shown in fig. 3.56.

Rice. 3.56. Pinout and pin assignment of the microcircuit KR (KF) 1211EU1A

Table 3.12. Differences of microcircuits with different markings

Maximum values ​​of parameters and modes:

• supply voltage V_cc - 12 V;
• high level input voltage V_IN (N) inputs IN, FV, FC - F_CC +0,5B;
• low level input voltage V_IN (L) inputs IN, FV, FC - -0,5 V;
• maximum output current I_OUT - 250 mA;
• power dissipation P_D - 750 mW;
• maximum load capacity C_L - 1000 pF.

Electrical specifications:

• supply voltage V_CC - 3.. .9 V;
• high level input voltage V_IN (H) inputs IN, FV, FC, not less than - 0,7V_CC;
• low-level input voltage Vm (L) on inputs IN, FV, FC, no more than - 0,2V_CC;
• average output current for each output I_OUT (av) - 150 mA;
• master oscillator frequency f_T, not more than - 5 MHz;
• high level input current I_IN (H) inputs IN, FV, FC, no more than - 1 μA;
• low level input current I_IN (L) inputs IN, FV, FC, no more than - 1 µA;
• consumption current at f_т = 0, no more than - 10 μA.

Description of work. The block diagram of the 1211EU1/A microcircuit is shown in fig. 3.57.

Rice. 3.57. Structural diagram of the microcircuit KR (KF) 1211EU1L

Summary feature microcircuits KR (KF) 1211EU1 - the presence of two sufficiently powerful key control channels operating in antiphase with a mandatory pause between output pulses. The impulse in the second channel appears some time after the end of the impulse in the first one, and vice versa; in Western terminology, this pause is called dead time - idle time. Due to this, the microcircuit is well suited for building simple, easily repeatable pulse voltage converters.

The microcircuit consists of:

• master oscillator;
• frequency divider;
• pulse shaper;
• output amplifiers.

Chip management is made through the outputs IN, FC, FV. Built-in threshold devices are connected to the control pins of the microcircuit. The IN pin toggles the frequency divider and resets the RS trigger blocking the pulse shaper and output amplifiers. When a low level voltage is applied to the IN pin, the division factor K1 is selected and the RS-trigger is reset, when a high level is applied, the division factor K2 is selected.

The FC and FV pins are used to build protection circuits. Applying a high level voltage to the FV pin causes the output amplifiers to turn off (voltage is set to zero on the OUT1 and OUT2 pins) for the time that the high level voltage is held at this pin. Applying a high voltage to the FC pin causes the RS flip-flop to be set and the output amplifiers to turn off (voltage is set to zero at the OUT1 and OUT2 pins) until the RS flip-flop is reset at the IN input.

The operating frequency of the master oscillator of the microcircuit depends on the parameters of the circuit elements R2, C1 connected to the output T.

The current flowing through the resistor R2 charges the capacitor C1. When the voltage on it rises to a level equal to about 2/3 of the supply voltage, the internal key of the microcircuit that shunts it opens, as a result of which the capacitor quickly discharges. Then the cycle repeats. The oscillation frequency f at the input T of the microcircuit can be estimated by the formula

For stable operation of the device, the capacitance of the capacitor C1 must be no more than 3000 pF, and the resistance of the resistor R2 must be at least 500 ohms.

Sawtooth pulses at the input T (Fig. 3.58) serve as the basis for the formation of output pulses at the outputs OUT1 and OUT2. Rectangular pulses alternately appear on them, the duration of which depends on the voltage level at the IN input.

Rice. 3.58. Timing relationships between input and output signals

At a low logic level, it is equal to six, and at a high - eight periods of oscillation of the master oscillator. At the end of the pulse, a pause is formed with a duration equal to one oscillation period of the master oscillator, during which the voltage at both outputs is low. Then a pulse appears in another channel, and so on. In other words, the pulse repetition rate at the outputs of the microcircuit f_O is related to the frequency f by the following relations: at a low level at the input IN

at a high level at the input IN

Here, the sums of the numbers in the denominators are the oscillation periods at the outputs OUT1 and OUT2, expressed in terms of the oscillation period at the input T.

The dependence of the stability of the generator frequency on the change in the supply voltage can be estimated from the graph shown in fig. 3.59. The current consumed by the microcircuit increases with increasing frequency of the generator, as shown in Fig. 3.60.

The output of the generator is connected to a controlled frequency divider, from the output of which symmetrical antiphase pulses are fed to the input of the shaper; the shaper provides a pause between them with a duration of one period of the clock frequency, as shown in Fig. 3.61. A typical scheme for using the 1211EU1 / A microcircuit in electronic ballasts for a fluorescent lamp with a power of 9-15 W is shown in fig. 3.62.

The inverter circuit consists of a 1211EU1 / A microcircuit with timing circuits and a push-pull transformer stage, the load of which is an oscillatory circuit L2, C8 with a fluorescent lamp.

Rice. 3.59. The dependence of the pulse repetition period at the output of the 1211EU1 microcircuit on the supply voltage; division factor is 14

After turning on the circuit heats the cathodes of the lamp with a voltage with a frequency 30% higher than the resonant one, and then supplies it with a high voltage with a frequency equal to the resonant one, under the influence of which the lamp begins to glow in the normal mode.

Rice. 3.60. Dependence of current consumption on generator frequency and temperature

The frequency of the pulses generated by the generator is selected such that at a high voltage level at the input IN (with a division factor equal to K2), the pulse repetition frequency at the output of the microcircuit is equal to the resonant frequency of the oscillatory circuit.

Rice. 3.61. Inverter Timing Diagrams

Rice. 3.62. A typical circuit for switching on a 1211EU1 / A microcircuit in an electronic ballast for a fluorescent lamp with a power of 9-15 W (click to enlarge)

When the supply voltage is applied, the current flowing through the resistor R2 begins to charge the capacitor C2 connected to the IN pin. The time constant of the RC circuit R2, C2 determines the heating time of the lamp cathodes.

In this case, during the time when the threshold value of the voltage at the input IN is reached, the cathodes of the lamp are heated with a frequency higher than the resonant one (division ratio K1), and after reaching the threshold value, the lamp is ignited and glows (division ratio K2). For this circuit, the resonant frequency of the oscillatory circuit is 45 kHz, the charge time of the capacitor C2 is 2 s.

Elements L1, C5 and C6 provide a change in voltage at the drains of transistors according to a sinusoidal law. The transistors switch at zero drain voltage, which reduces the heating of the transistors by reducing switching losses.

The 1211EU1A microcircuit differs from the 1211EU1 in the lower values ​​of both division factors K1 and K2 (see Table 3.12) of the frequency divider, which makes it possible to approximately halve the frequency of the master oscillator f_т. This is done so that the duration of the pause between the output pulses, equal to one period of the clock frequency f_т, has also approximately doubled, which makes it possible to effectively use inexpensive bipolar transistors with a longer switching time as output switches than those of field-effect transistors.

In addition to the field effect transistors indicated in the diagram, you can use KP742, KP723, IRLR2905, STD20NE06L, SPP80N04S2L, SPP80N06S2L.

As a step-up transformer T1 for lamps up to 15 W, armored cores of the cup type B22 (where 22 is the outer diameter of the cup in millimeters) without a gap, ferrite grade 2000NM are used. Winding II contains 150-170 turns of PEL with a diameter of 0,3 mm, winding I - 2x18 turns of PEL with a diameter of 0,6 mm.

For an LL with a power of 18-36 W, a more powerful core, W-shaped or armored, with an average core section of 0,6-1 cm2 should be taken. The main geometric parameters of some magnetic cores are presented in table. 3.13.

Table 3.13. The main geometric parameters of some magnetic circuits

Notes to the table. 3.13: K - ring magnetic conductors; Ш - Ш-shaped; B - armored. S_M, cm2 - effective value of the cross-sectional area of ​​the magnetic circuit; S_O, cm2 - area of ​​the magnetic circuit window; V_M = I_MxS_M, cm3 - effective volume of the magnetic circuit.

The number of turns of the primary winding is determined on the basis of 1-1,4 turns per 1 V of the supply voltage, the wire diameter is based on the current density of 3-4 A/mm2. For example, with an average primary current of 2 A, a wire with a diameter of 0,8-1 mm should be used. Similarly, the number of turns of the secondary winding is calculated, while the amplitude of the pulses must be at least 150 V.

The current limiting choke L2 is similar to the chokes used in the IR2153 electronic ballasts discussed above.

Application notes. Increasing the supply voltage increases the voltage supplied to the lamp and the power dissipated by the microcircuit. To avoid failure of both the lamp and the power transistors, blocking is introduced into the electronic ballast circuit for exceeding the supply voltage (FV output) and the consumed current (FC output).

The scheme of the electronic ballast blocking unit for exceeding the supply voltage is shown in fig. 3.63.

Rice. 3.63. Output stage voltage protection circuit

An increase in the supply voltage leads to an increase in the voltage at the FV input. When the response threshold is exceeded, the output stages of the microcircuit are turned off (a voltage equal to zero is set at the outputs OUT1 and OUT2). The level of operation of the protection circuit (maximum allowable voltage V_{P MAX}, supplied to the output stage) is determined by the choice of resistor values ​​R1, R2:

where 0,6V_CC - threshold of operation of the protection circuit.

Resistor R1 must be large enough to limit the current through the internal protection diode during large supply voltage surges.

The current protection circuit of the output stage is shown in fig. 3.64.

Rice. 3.64. Output stage current protection circuit

In the event of a lamp failure, the current through the lamp increases sharply, which leads to an increase in the voltage drop across the lamp filaments. This voltage is rectified by the detector VD1, C1 and is fed through the divider R1, R2 to the input FC. To prevent accidental operation from interference, a capacitor C1 is connected in parallel with the resistor R1. The divider R1, R2 must be calculated so that at the maximum allowable current through the lamp, the voltage at the FC input is 0,6V_CC.

On fig. 3.65 shows a diagram of an electronic ballast with protection of power keys.

Rice. 3.65. Scheme of electronic ballast with protection of power keys (click to enlarge)

This circuit is similar to the circuit shown in Fig. 3.62, but supplemented with protection nodes. Additional resistors R3, R4 and jumpers XI, X2 allow you to reduce the operating frequency of the master oscillator by 5, 10 and 15%. Elements VD1 and R5 provide protection against power surges. With increasing supply voltage V_p up to 17 V, the zener diode VD1 opens, the voltage at the input FV will be 5 V, which corresponds to the threshold of the protection circuit. The voltage at the terminals OUT1, OUT2 will then become equal to zero, the transistors VT1, VT2 are closed. Resistor R6 limits the current on the FV input to 5 mA for voltage surges up to 100 V.

Resistor R11 is a current sensor. The voltage from it is supplied to the detector VD3, C8 and then to the input FC. Selecting the resistor R11, set the threshold I_MAX current protection trips:   

If necessary, this value can be recalculated taking into account the transformation ratio of the transformer T1 into the current consumption from the power source. Elements R7, R8, C5 allow you to limit the voltage surges at the drains of field-effect transistors VT1, VT2 at the moments of switching at the level of 0,2V_p. The load characteristic of the microcircuit is shown in fig. 3.66.

Rice. 3.66. Load characteristic of the microcircuit

Author: Koryakin-Chernyak S.L.

See other articles Section Ballasts for fluorescent lamps.

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