In this post, we will offer you a new look at the now classic half-bridge driver of the type IR2104 - IR2109 - IR2184, the possibilities of which are not limited to passport data, assuming only amplification of the input signal. We will unleash its full potential, and learn how to make a PLL generator and a protected amplifier from this driver - in one person! The circuits obtained here are suitable for generators, boost converters, inverters and other devices, where it is required to obtain resonance in the output inductive (transformer) circuit. The circuits can also be used to excite a Tesla transformer, but with some conditions described below.

The simplest way to obtain automatic resonance in the output transformer is known - this is the ZVS driver circuit. The disadvantage of such a solution will be a difficult start, lack of protection and large losses in the chokes of this driver. The half-bridge driver has more advanced circuitry, which is distinguished by the absence of these shortcomings. But according to the declared passport characteristics, it does not work as a generator, especially as a resonant one. Such a driver requires a binding of several microcircuits, one of which is a PLL device. We talked about this option in of the previous part of this work. Here we will try to get by with simpler solutions and for this we will introduce two feedback loops into the driver circuit: PH180 and PH0 (Fig. 1).

Fig.1. Block diagram of half-bridge driver piping with generator and PLL

PH180 will provide negative feedback to keep the circuit unstable, and PH0 is positive feedback to create a generator mode. For the latter, the value of the current in the output circuit is required, which can be provided by the current transformer TA1. The overall goal is to make the positive feedback stronger than the negative one. And since hysteresis threshold elements are installed at the IN input, inside the DA1 microcircuit, then smooth changes in voltage on it will not lead to undefined states at the output: on the output transistors VT1-VT2. This is what we need.

Also, it is necessary to take into account possible sudden changes in the load, which, in resonant states at the output of the circuit, can give strong voltage drops. In this case, it is necessary to protect the output transistors and the DA1 microcircuit. This can be done by introducing feedback, which is included at the center point of the series circuit connected to the output of the circuit, consisting of capacitance Cr and inductance Lr (Fig. 2). This feedback is presented here as a PR1 block. Its task is to react quickly enough to exceeding the threshold voltage and turn off the output transistors, and then hold the protection for a certain number of periods.

Fig.2. Structural diagram of a half-bridge driver piping with a generator, PLL and overvoltage protection

The implementation of the feedbacks proposed above in practice is as follows. PH180 can be performed on a transistor VT3, which is connected through a resistor R5 to the output of the half-bridge and inverts this signal (Fig. 3). This maintains an unstable driver mode, which is a prerequisite for generation. The very same generation occurs due to the feedback chain, consisting of the current transformer TA1, and the phase-shifting circuit R4C4. Since the output of the half-bridge circuit will be connected to a resonant load of capacitance and inductance connected in series, then for positive feedback, which will promote maximum resonance, it is necessary to control the current, which is what the current transformer does. But at resonance, the current is shifted relative to the voltage by 90 degrees, hence the voltage across TA1 will have the same shift (Fig. 7). This shift is compensated by a chain of series-connected R4-C4, after which it is fed to the IN input of the driver, which is additionally protected from overvoltage by a zener diode ZD2. This is how the PH0 feedback is realized.

Fig.3. Schematic diagram of a half-bridge generator with a PLL

If overvoltage protection is not required, then the generator circuitry (Fig. 3) turns out to be quite enough in practice. It can be used in devices where the load is constant. Where the load resistance can change, it is necessary to apply protection: block PR1 from Figure 2. This can be done on one transistor VT4, which will be connected to the load through a chain of resistances R10-R13 (Fig. 4). When it is opened, the inverse SD input of the DA1 driver will turn off the output transistors. The VD4 LED indicates the protection process, and the capacitor C8 supports the circuit shutdown for several tens of milliseconds.

Fig.4. Schematic diagram of a half-bridge generator with a PLL and voltage protection

Instead of one resistance in the protection feedback circuit, three resistors R11-R13 connected in series are used, since the voltage at the point of their connection can reach rather high values.

A typical turn-on of the generator obtained above is shown in Figure 5a. There it is shown as a GG1 block. Its output XS4-XS4 is connected to a resonant load, consisting of a capacitance Cr and an inductance Lr, and the XS5 input is connected between them for voltage control and protection. By the way, in these schemes Cr and Lr can be swapped.

Figure 5b shows a 24V-220V DC-DC converter circuit. For example, at Lr = 800 uH, Cr = 0.2 uF, it converts the 24V supply voltage into the 220V supply voltage, with the active load Rn power of 200 W and a sufficiently high efficiency. When using a closed magnetic circuit as the core of the Lr coil, a small gap of 1-2 mm must be made in it.

Fig.5. Various options for enabling the GG1 generator

Generally speaking, with the element base indicated below and the given ratings - TA1, R3, R4, C4 - these circuits work well with a Cr capacitance in the range of 0.1 .. 0.5 uF, and with an inductance of Lr - 0.25 .. 1 mH. For other parameters Cr, Lr or TA1, select R3, R4, C4. It is also worth noting that at high currents through these elements, the Cr capacitor must be designed for the corresponding reactive power, and the diameter of the inductance wire Lr for the corresponding current.

Photos 6 and 7 show oscillograms of the processes occurring in the circuit connected to the load, for example, in Fig. 5b. To obtain photo 6, the blue oscilloscope probe is connected to the XS4 output, and the yellow one to the midpoint between Cr and Ls. The probe divider for the blue beam is set at 1:10, and for the yellow one at 1:100. The supply voltage of the circuit is 41V, the resistive load Rn is not connected. As we can see from this photo, the amplitude of the voltage across the reactive elements is approximately 15 times higher than the supply voltage. This mode, by the way, can be used by researchers for experiments where it is required to obtain large reactive energy in the circuit.

Fig.6. Voltage at the output of the circuit (blue beam) and voltage in the resonant circuit (yellow beam)

Fig.7. Resonant circuit voltage (yellow beam) and current transformer voltage (blue beam)

The image in Figure 7 can be obtained by connecting the blue oscilloscope beam to the output of the current transformer TA1. The resonant mode of operation of the device is very clearly visible here: the current in the resonant circuit is shifted relative to the voltage by 90 degrees.

Another version of the circuit is shown in Figure 8. The brand of the DA1 driver microcircuit, which has a slightly different pinout, and the method of obtaining the +12V internal power supply due to the introduction of the DA2 voltage stabilizer, were subject to change here. The advantage of such an inclusion is less heating of the damping resistance R8, which means a slightly higher efficiency of the entire device.

Fig.8. Schematic diagram of a half-bridge generator with a PLL and voltage protection (second option)

It is this version of the circuit that is proposed below as an industrial version.

List of circuit elements. Valid substitutions are given in parentheses:

• DA1 - half-bridge driver: IR2104 or IR2109 - for scheme 3 and 4, IR2184 (IRS2184) - for scheme 8;
• DA2 (for scheme 8) - 12 volt voltage regulator L7812;
• VT1-VT2 - mosfet transistors. At supply voltages up to 80V, circuits work fine IRFP4568 (IRFP260), more than 80V - better suited 47N60 or similar;
• VT3-VT4 - n-p-n transistors S8050;
• VD1-VD3 - diodes UF4007;
• VD4 - LED red;
• ZD1-ZD2 - unidirectional suppressors 1.5KE12A. In diagram 8, ZD1 is 1.5KE33A;
• TA1 - current transformer ACST-003. For other brands - you need to select R3, R4 and C4;
• R3, R4, R8 - 2 W resistors;
• C4, C6, C7 - polypropylene capacitors with an operating voltage of 250-400V;

The circuit must be connected to the load as shown in Figure 5. It is necessary to start testing the circuit with relatively small values of the supply voltage, for example, with 24V. At the same time, stable sinusoidal oscillations should appear on the load. If this does not happen, then Lr or Cr are selected incorrectly and selection of R3, R4 and C4 is required. Alternatively, the current transformer may be turned on incorrectly, then its outputs just need to be swapped. After receiving oscillations, it is necessary to increase the supply voltage to the operating values, and set the protection operation with the trimming resistance R10. This can be done, for example, by disconnecting the load Rn, after which the voltage at the point where Lr and Cr are connected will jump sharply. It is also limited by the protection scheme.