Isolated Gate Driver Anti-Circuit for PWM Voltage Clamping
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Solution Overview
Problem
Conventional isolated gate drivers fail to reliably drive high power MOSFETs due to induced voltages exceeding the maximum gate-source voltage, especially when the duty cycle of the PWM signal is sharply decreased, leading to incorrect turn-on and turn-off states.
Innovation Solution
An isolated gate driver is designed with an anti-circuit and secondary processing circuit to suppress induced voltage variations and perform voltage clamping, using diodes and capacitors to filter and regulate the PWM signal, ensuring the gate-source voltage remains within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the turns ratio of the isolated transformer is 1:1, then the circuit configuration is simple, but the induced voltage in the secondary winding exceeds the maximum gate-source voltage when the duty cycle is small
Solution Approach 1:
A voltage regulation circuit is introduced as an intermediary between the transformer secondary winding and the MOSFET gate. This circuit includes a voltage regulation element (such as a zener diode or voltage regulator) that mediates the voltage transmission, ensuring the gate-source voltage does not exceed the maximum rated value even when the transformer induces higher voltage during small duty cycles.
Solution Approach 2:
The voltage regulation circuit dynamically adjusts the gate-source voltage parameter based on the induced voltage from the transformer. When the duty cycle causes excessive induced voltage, the regulation circuit clamps or limits the voltage to remain within the safe operating range of the MOSFET, thus changing the voltage parameter adaptively.
2Productivity
If the duty cycle is sharply decreased, then the switching frequency increases, but resonance causes induced voltage to sharply vary and exceed maximum gate-source voltage
Solution Approach 1:
The voltage regulation circuit is designed to anticipate and cushion against voltage spikes caused by resonance. By pre-configuring voltage clamping elements and filtering components, the circuit prepares to absorb or limit voltage variations before they can damage the MOSFET, ensuring stable operation even during sharp duty cycle changes.
Solution Approach 2:
The voltage regulation circuit implements feedback control by monitoring the induced voltage from the transformer secondary winding. When voltage exceeds the maximum gate-source voltage due to resonance, the feedback mechanism activates the regulation element to clamp the voltage, creating a closed-loop control system that maintains voltage stability.
3Ease of operation
If the induced voltage sharply varies due to resonance, then the voltage regulation becomes difficult, but the MOSFET may be mistakenly turned on
Solution Approach 1:
The voltage regulation circuit applies preliminary anti-action by pre-configuring voltage clamping and filtering elements that counteract resonance effects before they can cause harmful voltage variations. The circuit is designed to resist voltage spikes proactively, preventing the conditions that would lead to mistaken MOSFET turn-on.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents false turn-on and turn-off states, ensuring reliable operation of the power switch tube across a wide duty cycle range, with enhanced anti-interference capabilities and simplified circuit configuration.
Implementation Method 1
The isolated transformer has a primary winding and a secondary winding... the induced voltage VS (i.e. (1−D)*Vcc1)... the induced voltage VP in the primary winding LP
Implementation Method 2
The capacitor is connected in parallel with the first diode... filter out a DC component of the driving PWM signal
Implementation Method 3
An anode of the first diode is connected to one terminal of the primary winding... An anode of the second diode is connected to one terminal of the secondary winding
Data Source
AI summary
An isolated gate driver including a driving control circuit, an isolated transformer, an anti-circuit and a secondary processing circuit is provided. The driving control circuit is configured to generate a driving PWM signal for driving a power switch tube. The isolated transformer has a primary winding and a secondary winding. The anti-circuit is connected between the driving control circuit and the primary winding of the isolated transformer, and is configured to suppress a variation of an induced voltage in the secondary winding of the isolated transformer when a duty cycle of the driving PWM signal is sharply decreased. The secondary processing circuit is connected in parallel with the secondary winding of the isolated transformer, and is configured to perform a voltage clamping action on a gate-source voltage of the power switch tube when the duty cycle of the driving PWM signal is sharply decreased.