JPH0619354Y2 - Driving circuit for fan motor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a drive circuit for a motor used in an electric fan.

<Prior Art> Generally, when controlling an induction motor using a TRIAC for full-wave operation, the gate current of the TRIAC may be continuously supplied, but it is often desirable to reduce the average gate current value by the trigger pulse method. Occurs.

The present invention provides a drive circuit having an efficient trigger pulse generation circuit for controlling the gate current as small as possible when the load current is as small as the holding current of the triac under such conditions. Is.

<Example> When the load current is sufficiently larger than the holding current of the triac, the current waveform of the trigger pulse is as shown in FIG.
Even if the pulse width is small at the timing of zero crossing of the current waveform, full-wave drive of the load is possible. When the load current is smaller than the holding current of the triac, the triac becomes less than or equal to the holding current near the zero cross of the current waveform, so the triac may be turned off during this period. In order to stably maintain the operation of the triac during this period, it is necessary to flow a sufficient gate current during this period.
Therefore, in this case, it is necessary to widen the pulse width of the current waveform of the trigger pulse around the zero crossing timing of the current waveform as shown in FIG.

Consider a more efficient trigger pulse. Since the load current increases as the phase advances or lags with respect to the zero-cross timing of the load current waveform, on the contrary, the gate current may be small. When the load current waveform is a sine wave, the trigger pulse current waveform shown in FIG. 3 is the most efficient waveform.

Next, FIG. 4 shows a trigger pulse generation circuit, that is, a circuit example of the present invention, which easily realizes a current waveform that approximates this efficient trigger pulse.

The zero-cross detection circuit and microcomputer, generates the microcontroller output pulses as shown in optimum timing i.e. Figure 5, resistors R _1, R _2, R ₃ capacitor C, by a circuit composed of transistors Q, as shown in FIG. Voltage waveform across the resistor R ₄ (current waveform has the same shape)
Is obtained. This is a good approximation to the efficient trigger pulse current waveform shown in FIG.

However, the timing of the current waveform of this trigger pulse is
Timing of microcomputer output pulse and resistance R ₁ , R ₂ , R
_3. Since it changes depending on the constants of the capacitor C and the characteristics of the transistor Q, these must be properly determined.

<Effect> With a simple circuit configuration, the gate current is small, and stable full-wave driving of the TRIAC can be performed.

[Brief description of drawings]

 1 to 3 are waveform diagrams, FIG. 4 is a circuit diagram of an embodiment of the present invention, and FIG. 5 is a waveform diagram based on the circuit.

Claims (1)

[Scope of utility model registration request] 1. When a full-wave drive of an induction motor having an extremely small current by using a triac, the gate current is reduced,
Moreover, in order to perform stable triac ignition, the gate current of the zero cross phase of the load current waveform is maximized,
As a result, a fan motor drive circuit including a triac trigger pulse generation circuit that controls the gate current to gradually decrease as the phase advances or delays.