Slope compensation question

灞波儿奔

Slope compensation question [Copy link]

I would like to ask about the slope compensation problem of the power IC chip UC3843.

As shown below

Slope compensation problem
The following circuit is a triangle wave signal generated by the Rt and Ct oscillation circuit in the UC3843 circuit.

The manual recommends using an emitter-follower composed of transistors to introduce slope compensation. How to apply slope compensation in the actual circuit? Since the waveform of RT/CT is a triangle wave from +1V to +3V, won’t the voltage be too high if it is directly added through the emitter of the transistor?

If not high, why?

Should capacitors be used to block DC?

maychang

"Because the waveform of RT/CT is a triangle wave of +1V to +3V, wouldn't the voltage be too high if it is added directly through the emitter of the transistor?"

The voltage on the RT/CT pin is divided by the R RAMP resistor and the R CSF resistor before being applied to the I SENSE pin.

maychang

"Should I use capacitors to block DC current?"

Capacitors should not be used for DC isolation.

maychang

"Should I use capacitors to block DC current?"

If a capacitor is required for DC isolation, the chip manufacturer will indicate this in the datasheet and mark it in the diagram.

灞波儿奔

maychang posted on 2022-1-17 18:29 "Should capacitors be used to block DC current? " If capacitors should be used to block DC current, the chip manufacturer will definitely indicate this in the datasheet and in the diagram...

Thanks for the answer

Does this transistor also play an isolating role?

Can I use capacitors to block DC? Why not?

maychang

灞波儿奔 posted on 2022-1-19 14:16 Thanks for your answer. Does this transistor also play an isolation role? In addition, can capacitors be used to isolate DC? Why not...

"Can I also use capacitors to block the DC current? Why not?"

After the capacitor is isolated, only the AC component of the triangular wave generated by RC (after voltage division) is applied to the current detection pin. In other words, the signal applied to the current detection pin (after voltage division) is both positive and negative.

In addition, using capacitors to block DC current will not provide any compensation.