Power supply of the PWM controller chip and gate drivers with stabilized voltage. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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In many practical designs of automotive PVs, the PWM controller chip (for example, TL494, SG3524, etc.) is powered directly from the REMOTE input (see the descriptions of the PV amplifiers MTX and Jensen) through a directly connected protective diode. In the presence of an external gate driver (inverter, repeater), the current consumption from the REMOTE bus does not exceed 20 mA and thus fits into the capabilities of any head unit. When the controller IC operates directly on the gates of the MIS keys, its average current consumption increases to 50-80 mA (the thermal limit for an IC in a DIP16 package is 1 W at 45C). Which is also unlikely to overload the REM signal source. Then why invent a separate regulator or switch to power the controller IC?

But why. The gate of an MIS transistor is just a non-linear capacitance. Moreover, it is nonlinear only until the channel is fully opened (saturation), then it can be confidently considered a simple capacitor. Depending on the temperature, a conventional MIS transistor starts to open at Uzi = 2-4V, saturation, depending on T, Ic and Usi, occurs at a voltage of about 5-10V. For example, for IRFI 1010N (an excellent low-resistance key) at 25C, the maximum passport current of 49A is achieved at 6V, at 175C - at 6.5V at the gate (gate charge is about 60 nC).

If the gate voltage continues to grow, then ... the current and thermal power limit will definitely not change from this. On the other hand, an excess positive charge will appear on the gate - about 6 nC for each volt, and at + 12V on the gate it reaches 100 nC.

But when the transistor is closed, we definitely do not need an excess charge. After all, until those same 100-60 = 40 nC of the "extra" charge flow through the gate driver to the ground, the transistor is still open at full strength. This is both an unnecessary turn-off delay and an extra load on the gate driver (forcing you to install unreasonably powerful repeaters).

Let's guess. The voltage of the on-board network is 14V. At the output of Remote - 13V. Minus 0.6V on the diode = 12.4V power supply of the microcircuit. If its output transistors (Darlingtons) are turned on by an emitter follower, the output pulse reaches 11.0V. An external repeater will take another 1V. Total - 11V without an external driver, 10V with one. There is an excess.

What to do? Feed the entire excitation circuit (ICs + drivers) from a linear regulator that provides exactly as many volts of supply as needed. And you need: 7V at the gate + 0.7V at the follower + 1.3V at the IC transistor = 9V total. And so that it was with a margin - 10V.

Moreover, it is desirable to take the supply current from the battery, and turn on the stabilizer with a weak current from the Remote bus. And to have fewer unnecessary details.

The LM2931, the Soviet analogue of 1156EN5, is ideal for solving the problem. But only in a 5-pin transistor package! (there are options with fixed Uout, with 3 outputs).

This circuit is specially designed for automotive applications. Features compared to conventional 3-pin regulators:

- Adjustment of output voltage 1.2-36V, output current up to 100 mA.

- Voltage drop at 100mA - 300mV typical, 600mV maximum.

- Disconnection of the load in case of power reversal and emergency excess of power supply (protection against impulses -50 ... +60V, DC voltage -30 ... +36V).

- Remote start by a positive logic signal (requires 1 external npn transistor, driving current up to 50 µA).

- Current consumption is not higher than 1 mA

This is what the simplest typical inclusion looks like:

The output voltage is set by the R4/R5 divider: U=1.2V * (R4+R5) / R4. The value of R4 (1.2V of the reference voltage drops on it) is up to 51 kOhm, it can be less. R3 - from 10 to 51 kOhm. Transistor - any low-power with a small reverse collector current.

The IC turns on when the voltage at input Adj (collector Q1) drops below 2V. The capacitors shown in the diagram provide stability to the regulator and should be placed directly next to the IC pins. Impulse load (PWM controller, repeaters) - shunt with local ceramic capacitors.

The input transistor can be replaced by a transistor optocoupler (with low leakage current), with a suitable ballast resistor in the primary circuit - then immunity to control input noise is guaranteed.

Literature

1. "Microcircuits for linear power supplies", Dodeka, Moscow 1999

Publication: klausmobile.narod.ru

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